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INTEGRAL Science Data Centre SPI Analysis User Manual

1. Parameters characterizing event binning dtype integer If the PHA outputformat option is selected the binned data can be generated in units of counts 1 counts s bin 2 or counts s keV 3 You have to choose the desired format and enter the corresponding number e g 1 psdtype string Determines which type of PSD selection is desired There are 2 PSD flags one in the raw data which is created by the on board software and one in the corrected corr data which is created on the ground The user has the option of selecting raw or corr The value of the PSD flag 0 or 1 indicates whether a PSD event is characterized by single or multiple peaks e g raw detnums string Specifies the detectors for which binned data are produced The detectors listed here should be a subset of the ones used in spi_gti_creation To use a full set you should enter This option is only available if the outputformat parameter is set to PHA e g ISDC SPI Analysis User Manual Issue 0 9d1 35 multipointing This parameter let you to choose whether summed or distinct pointings are to be processed To enter you selection you should type either d or p e g d tstart The start of the spectra accumulation time interval If the value is INDEF tstart is taken from the pointing definition e g indef The end of the spectra accumulation time interval If the value is INDEF tstop is taken
2. 1 are analyzed and their fluxes and lo errors written to the output catalogue After the image is produced the flux and its error for a number of user defined sources can be optionally determined Each source is specified in terms of a position and ON and OFF radii The ON region is the circle centered on the source position with radius ON and the OFF region is the annulus between the ON and OFF radii The source flux is defined as X intensity in ON region X intensity in OFF region solid angle ON solid angle OFF The error is based on a Bayesian analysis which marginalizes over all the unwanted degrees of free dom so the significance of a source by this method may not correspond to a classical significance level In general significances increase for smaller skymaps since the degrees of freedom decrease The spiskymax parameters most important for the first try are the following Input Output rogroup string DOL of the input fits file which identifies the observation group to be processed rwgroup string DOL of the output fits file e g og spi fits GROUPING irf input file string DOL of the IRF index file with SPI response information e g ic spi rsp spi irf grp 0007 fits GROUPING source cat dol string DOL of the input catalogue e g source cat in fits 1 ISDC SPI Analysis User Manual Issue 0 9d1 47 Output image definition image idx string DOL of the output skyma
3. Detector_Spectra Background_Model Source_Catalogue IRF Sky_Images Back_Detector_Spectra Source Results Figure 9 Scientific Analysis Preparation and ISDC SPI Analysis User Manual Issue 0 9d1 Source Detector Spectra Imaging Analysis 21 Computes the ratio of the dead time to the live time dead ratios and live times within the good time interval for all detectors and pseudo detectors spidead BIN I Event Binning for Imaging Defines the energy bins to be used for imaging selects good events within the GTI and creates detector spectra for all detectors and pseudo detectors Spectrum values are express in counts or in rates dividing counts by the live times spibounds BKG I Background Generation for Imaging Derives estimated background detector spectra from models or observation data and stores them in background data structure spiback CAT I Catalogue Source Selection for Imaging Selects a list of known sources from the ISDC reference catalogue or from previous analyses and creates a source data structure containing source location and expected flux values RSP_I Image Response IRF Derivation TBD IMA Image Reconstruction Generates sky images and search for significant sources If sources are detected a new source data structure is created including a copy of the input source data and the newly derived source properties such as
4. The passive mask is located at the top of the SPI instrument above the plastic scintillator The purpose of the mask is to code the incident gamma rays in the field of view giving the instru ment imaging capabilities The mask also provides stiffness to the primary structure of the SPI instrument The mask consists of a sandwich structure made of ISDC SPI Analysis User Manual Issue 0 9d1 3 e a honeycomb core covered by two skins e a titanium ring that forms the interface to the rest of the instrument e a coded motif made of hexagonal tungsten blocks that are stuck and screwed onto the sand wich structure Motif is symmetric for 120 rotation The tungsten motif provides the specific transparency and geometry for the mask The mask is made of 127 elements of hexagonal shape and inscribed in a 78 cm diameter circle Of these elements 63 are opaque and 64 are transparent Each opaque element is 30 mm thick and 60 mm flat to flat in size The tungsten elements stop the gamma ray radiation in the range 20 keV to 8 MeV with an absorption efficiency greater than 95 at 1 MeV The holes in the mask have a gamma ray transparency of 60 at 20 keV and 80 at 50 keV The mask is located 171 cm from the detector plane The distance between the mask and the detector plane is driven by the required field of view and angular resolution A picture of the mask pattern is given in Figure 2 minm Figure 2 The passive mask of the SPI
5. point sources and to adjust their positions and fluxes to give a best fit to the data This is the basic principle of the spiros method spiskymaz on the other hand regards the image as a pixelated skymap and the aim is to obtain the intensity in each pixel The most important idea is that the data constrain the image within some limits in an N dimensional space where N is the number of pixels Hence there is no unique best image and we have to make some choice out of all the possible images within the constrained region Maximum Entropy method as implemented here is one way of doing this and of quantifying the uncertainty of the result Since the number of pixels is usually large e g 10 109 the techniques involved are rather different from those of model fitting spiskymax is adapted to the particular needs of SPI The background temporal variations are treated via a template prepared by spiback and the coefficients are fitted during the imaging process The input count spectra contain data for many energy bins and spiskymaz analyses a subset or all of these energies as specified by the parameters energy_range_min energy range_maz The number of iterations can be specified since the automatic stopping criterion is not always appropriate and in any case may not be reached in the CPU time available Sources to be analyzed are defined by their positions in the input source catalogue SPI SRCL CAT only those with the SEL FLAG flag
6. As explained above dithering is required when imaging more complex regions 5 3 2 Spectral Resolution The spectral resolution has been measured in the laboratory with detectors that are representative of the flight units and afterwards with flight model detectors and pre amplifiers An example spectrum obtained in this way is shown in Figure 4 The measured energy resolution as a function of energy for an individual detector is given in Figure 5 The energy resolution for the full instrument is given in Table 4 The energy resolution does not depend strongly on the temperature of the detectors therefore even in the case of a failure of one of the coolers the spectroscopic capability of the instrument is not significantly degraded However a small drift in energy is observed as a function of temperature so a recalibration would be required 700 T T T T T capture Fe n gamma 600 F coublet 7631 1 7645 5 keV 4 300 F 4 alg I a 1 600 6800 7000 7200 7400 7600 7806 Counts see 4 Energy keV Figure 4 Example spectrum taken with laboratory detector units representative of the flight units 5 3 3 Sensitivity The continuum and line sensitivities of the SPI instrument are given in Figure 6 and Figure 7 In Table 4 the instrument performance numbers energy resolution continuum and line sensitivities are given at a number of energies in the SPI range The sensitivities given in this tab
7. achieved by making the detector as large as possible and by minimizing the background by using an ACS that is optimized in material and thickness by incorporating a PSD system by carefully choosing the materials used in the instrument and by adding a plastic scintillator below the mask The passive mask provides the shadowgram for image reconstruction The PSAC detects energetic particles originating in the mask and provokes a veto pulse from the veto system The ACS detects gamma rays and charged particles from out of field sources and also provokes a veto pulse Each photon that is absorbed in a Ge detector will give a pulse that is sent to the electronics The electronics analyses the incoming pulses and the veto signals and tags each photon with the energy the time and the type of event i e single detector events with or without PSD and multiple detector events These data are then sent to the ground see below The ACS off photons are summed into background spectra that are sent to the ground every 30 minutes 3 2 Operating Modes The SPI instrument has only one mode for normal observations All scientific observations with SPI are done in so called photon by photon mode with a high temporal resolution In this mode scientific data is collected and transmitted to the ground for each photon For each detected photon date is sent to the ground from which the type of event the energy and the timing can be deduced Furthermore detector s
8. it depends on several external conditions e g increase of the ACS rate during a solar flare and thus will only be known accurately after launch This takes also into account the dead time as a result of ACS vetoes BGO and plastic scintillator 3 4 Telemetry Budget The allocation of telemetry to the SPI instrument in photon by photon or TM emergency mode is 16 kilobits per second kbps in solar maximum and 20 kbps in solar minimum INTEGRAL uses packet telemetry Each packet corresponds to 0 44 kbps so the above allocations translate into 36 and 46 packets for solar maximum and solar minimum cases respectively The model calculations done by the University of Southampton England using the INTEGRAL Mass Model and by the SPI instrument team show that in solar maximum a rate of 8 events s det is to be expected although it might reach 12 events s det especially taking into account the contributions of background lines whereas in solar minimum this goes up to 20 events s det These events are split into 45 6 singles event detected by only one detector and not processed with a PSD 42 3 PSD events event detected by only one detector and processed with a PSD and 12 1 multiple events events detected by more then one detector The total telemetry rate then will be 17 packets per cycle in solar maximum 7 5 kbps and 41 packets per cycle in solar minimum 18 kbps In addition to the telemetry needed for the photon by photon data every 30
9. see Table 7 Individual detectors are specified by their detector numbers separated by commas A range of detector numbers can be specified by giving the first and last detectors in the range separated by a e g 0 84 good time index file good time index file without template or DOL e g goodtimeindex fits For each SPI pointing column PTID_SPI and each detector and pseudo detector column DET_ID the output GTI data structure SPI OBS GTI in the file spi gti fits contains the start and end times of the GTI columns OBT_START OBT_END TSTART and TSTOP and the total good time in seconds column ONTIME The schematic representation of this data structure can be found in Figure 15 8 6 Dead Time and Live Time spidead The executable spidead computes the dead and the live times for each SPI pointing and each detector and pseudo detector within the good time intervals defined by the SPI GTI file The dead times are defined by the DFEE It is assumed that the dead times do not depend on event energy The dead times for the double events are defined by the larger dead time of the two detectors involved Also for the triple events the detector with the largest dead time involved in the triple determines the deadtime chosen for this pseudo detector Input Output in og dol string Input Observation Group DOL dead time dol string Output dead time data structure e g spi dead_time fits SPT OBS
10. 3 for point sources depending on point source intensity Field of View fully coded 13 2 flat to flat fully coded 16 corner to corner zero coding 30 5 flat to flat 35 corner to corner zero sensitivity ISDC SPI Analysis User Manual Issue 0 9d1 2 2 Instrument Description 2 1 The Overall Design The SPI instrument design is based on a hexagonal geometry which is the most compact one The instrument is a coded mask spectrometer An overall cut out view of the instrument is given in Figure 1 Figure 1 A cut away view of the SPI instrument The mask plastic scintillator camera and ACS sub systems are highlighted The detector of the instrument consists of 19 cooled hexagonally shaped high purity Ge detectors providing a total area of about 500 cm The background on the detectors is limited by the use of several methods A Pulse Shape Discriminator system PSD reduces the 8 decay background in the Ge An Anti Coincidence Shield ACS consisting of 91 bismuth germanium BGO scintil lator blocks vetos out of field photons and particles and a plastic scintillator PSAC underneath the coded mask vetos charged particles The veto shield also defines the field of view of the in strument since it vetoes the out of field photons The sensitivity of the instrument is limited by the background due to the primary and secondary cosmic ray particles and the cosmic background radiation 2 2 The Passive Mask
11. This multiplicity can differ from that in the raw data if during the low level analysis it was decided for some reasons to redefine the time interval during which the signal measured by different detectors is assumed to ISDC SPI Analysis User Manual Issue 0 9d1 24 be related with the same incident photon 7 4 Instrument Characteristics used in Data Analysis In order to process your RAW and PRP data you need to know the instrument response and the results of the Calibration Analysis made at ISDC 7 4 1 Instrument Calibration During the Instrument Calibration the measured and expected energies width and channel posi tions of the lines used in Calibration Analysis are compared The results of the Calibration Analysis performed at ISDC are written to the file spi_gain_coeff fits The data structure SPI COEF CAL contains gain coefficients For a given OBT start stop and energy range the different coefficients connecting the channels and energies are stored as 19 vectors one for each detector 7 4 2 Instrument Response RMF data structures Figure 10 presents a few definition used it the following discussion Np and Ep are the number and the energy of the incoming photons and Nc i and the Ec are the number of the counts and the energy measured in the detector respectively Sky Nc i Number of counts in detector i Y degree Np Number of photons SRA SPI Ec Energy measured i
12. ate ta Pe ec van raya att DURER Prepared Data cir Be He ee eS eee ee BAER ERTS Instrument Characteristics used in Data Analysis o 7 4 1 7 4 2 Instrument Calibration 0 00 ee Instrument Response 2l 8 Scientific Analysis 8 1 Pseudo detectors Definition 0 2 0 000 000 0000 0020000 8 2 Build Observational Group og_create o 8 3 SPI Correction spi_gain_corr ee een 8 4 Pointing Definition spipoint aaa 8 5 SPI Good Time Handling spi gt creation o o 8 6 Dead Time and Live Time spidead 2s 8 7 Energy Bin Definition spibounds een 8 8 SPI Events Binning spihist 22h 8 9 SPI Background Generation spiback o o 8 10 Source Reconstruction and Spectra Extraction sp iros o 8 10 1 IMAGING mode een 8 11 Image Reconstruction spiskymav s ISDC SPI Analysis User Manual Issue 0 9d1 20 20 23 23 23 24 25 25 25 28 28 29 30 30 31 32 33 34 36 40 40 47 iv 9 Cookbook 9 1 Preparation inicias dd o e a a a A A YUxSQ WO 9 2 Example 1 image of the 511 keV line reference orbit test source 10 Known Limitations ISDC SPI Analysis User Manual Issue 0 9d1 Acronyms and Abbreviations AD Architectural Design ISDC Integral Science Data Center ADD Architectural Design Document OBT On Board Time ACS Anti Coincidence Shield ac Observ
13. choose between IMAGING SPECTRAL and TIMING e g IMAGING in og dol DOL of the input fits file which identifies the observation group to be processed out og dol DOL of the output fits file e g og spi fits GROUPING Instrument and Background response inst resp idx DOL of the file which provides the count response in all detectors of SPI due to a point source anywhere in the instrument field of view and at any source photon energy e g IRF SPTIRF index fits GROUPING background method integer Program spiback generates a first model of the background Pa rameter background method allows you following possibili ties O implies there is no background only good for calibration sources 1 implies the background values are given and will be subtracted from input counts first 2 implies background rates in each detector are to be calculated independently 3 implies background rates given in each detector are relative function values e g 3 Catalogue of known sources source cat dol DOL of the catalogue of known sources In IMAGING mode this parameter is not obligatory but saves spiros from searching for sources whose location is more or less known location max error If the input catalogue of known sources is specified then spiros compare the location errors of sources from catalogue with this parameter If they are LESS than it the source will be flagged as having a FIXED location and width whic
14. for e g fitting in XSPEC spectral mode e TIMING mode As in SPECTRAL mode a catalogue of known sources is used to create a light curve of sources and background in several energy bins one flux value per pointing 8 10 1 IMAGING mode Given its main task of locating point sources and creating images of them in the observation field of view the first question is how spiros goes about locating them A fast and simple method results by assuming some prior knowledge of the sources expected in the field of view namely that they are point or pointlike and that there are only a small finite number of them tens but not hundreds or thousands On this assumption the sources can be located using the Iterative Removal of Sources or IROS method which literally attempts to locate each source in the field of view one after the other from the strongest to the weakest This method works as follows e A fast but blurred location image is created which shows clearly the most probable location or region of the greatest source emission This image may be called a pixel independent correlation map as it is constructed by scanning the imaging field of view with a source probe and calculating the flux by assuming all input counts are due to that source and any background events alone This typically produces a convolved image with a global maximum at a good first guess for a probable source location e With this approximate location find th
15. instrument The bottom picture indicates the direction of the spacecraft Y and Z axes with respect to the mask 2 3 The Camera 2 3 1 Cryostat For an optimum sensitivity and resolution the detectors of the SPI instrument have to be kept at a constant low temperature of 85 K The SPI cryostat which is made in Be is designed to keep the detectors at this optimum operating temperature The cryostat is composed of three parts an active cooling system a passive cooling system and a cold box The active cooling system brings ISDC SPI Analysis User Manual Issue 0 9d1 4 the temperature of the cold plate on which the detectors are mounted down to 85 K using two pairs of cryocoolers In normal operating mode all coolers work simultaneously In case of failure of one of the cryocoolers or of the electronics the instrument will be functional but in a degraded mode as the detector temperature can rise to more than 100 K The detector assembly is placed inside the cold box which is kept at approximately 210 K by the passive cooling system All temperatures of the cryostat subsystems are regularly monitored to provide the ground operators with early warnings on failures of coolers and to provide temperature information that can be used for the data processing 2 3 2 Detectors and Pre Amplifiers The detectors used for SPI are 19 hexagonal shaped Be encapsulated high purity Germanium detectors mounted on a cold plate at 85 K as close as possi
16. is optimized This is done by making a compromise between getting the best signal to noise ratio for the pulses operating in the full 20 keV 8 MeV energy band of the instrument without resolution degradation and making the output pulses insensitive to the fluctuations in the detector signal rise time The PHA is used to maintain the energy resolution in the full 20 keV 2 MeV or 2 MeV to 8 MeV range Finally the detector electronics also comprise a high voltage power supply 0 5000 V and a low voltage power supply 19 independent chains per amplification chain 2 3 4 Pulse Shape Discriminator PSD The PSD subsystem compares the form of the pulses produced by the pre amplifiers with profiles stored in an on board archive Based on this comparison the PSD flags each event with a signal type single or multiple event and consequently the type of processing necessary Only non vetoed events are processed by the PSD The output of the PSD is provided to the Data Processing Electronics DPE see below The PSD works in an energy range from 200 keV to 1 MeV The on board pulse shape library will be updated twice a year in connection with the annealing of the detectors The PSD is important to identify the background photons impacting on the detector It can reduce the background between 200 keV and 1 MeV and thus increases the sensitivity of the instrument in this energy range ISDC SPI Analysis User Manual Issue 0 9d1 5 2 4 Anti Coinciden
17. list of SWG DOLs see Figure 14 ogid string Observation group id used to build the path baseDir string base directory from which the obs branch will be build This parameter should be a relative path from where og create is run instrument string Comma separated list of instruments This will create several OG in the same repository INTEGRAL all data SPI IBIS JMX1 JMX2 OMC Specific data ISDC SPI Analysis User Manual Issue 0 9d1 29 Additional parameters purpose string Scientific purpose of the OG optional versioning integer Add a version to the ogid directory 0 NO 1 YES 0 is the default value Example og create idxSwg dols txt ogid obs_id baseDir instrument SPI 8 3 SPI Correction spi_gain_corr SPI correction uses calibration data described in Section 7 4 1 to compute the event energy in physical units keV from the instrumental channel PHA No event randomization is included in this process i e the exact energy of the channel center is attributed to all events of a given PHA channel To run this program you should specify the following parameters Input DOL of the Prepared Observation Group to work with e g og spi fits GROUPING DOL of the PRP SWG optional in case only one SWG should be corrected instead of a whole observation group coeffDOL DOL of the calibration file containing the correction parameters e g spi_gain_corr spi g
18. minutes the ACS off spectra are transmitted This nominally requires 5 packets per cycle 1 9 kbps The total nominal SPI telemetry thus is 22 packets per cycle for solar maximum 10 kbps and 46 packets per cycle in solar minimum 20 kbps If needed the amount of telemetry in solar minimum can be reduced by increasing the low energy threshold to 100 keV but this is at the cost of loss of some science Changing the low energy threshold cannot be done by the observer but is done by the INTEGRAL ground segment if deemed necessary ISDC SPI Analysis User Manual Issue 0 9d1 8 4 Using the Instrument 4 1 Spectroscopy amp Timing In the standard observing mode the instrument can be used for spectroscopy and timing observa tions Since every photon is tagged with an accurate time these data can also be used for timing analysis It is expected that the background in each of the 19 independent detectors will vary in time in a different way This variation can limit the sensitivity that is obtainable Several types of background variations can be anticipated e short term variations due to solar activity and solar system weather e variations over the orbital period related to the position of INTEGRAL in the orbit e long term variations over the mission duration In order to reconstruct the image on the detectors for all pixels in the field of view 25 degree field with 2 degree resolution for a single pointing a set of 19 equati
19. using hexagonal dithering The integration times are 2x10 and 1 26x10 seconds respectively Calculations were done using the Observing Time Estimator Fluxes are in ph cm s After the Commissioning Phase the SPI team and the ISDC will calibrate the instrument using data taken during routine observations This will allow an accurate determination of e g the background Also lines originating in the BGO shield 511 keV 6 1 MeV O line can be used for calibration purposes e g energy calibration and lines that originate from materials inside the cryostat that have known intensities can be used to measure the Ge detector efficiency The detector gains thresholds and resolution versus energy are determined from normal event data and ACS off spectra for consistency checks in the routine monitoring task of ISDC Finally after every detector annealing a thorough check will be done of the instrument imaging and spectroscopic response since these may change as a result of the annealing process ISDC SPI Analysis User Manual Issue 0 9d1 13 5 3 Measured Performance 5 3 1 Imaging Resolution The true imaging resolution will only be known after launch since it depends on the background radiation The design of the instrument however is such that the angular resolution for isolated point sources is about 2 5 FWHM The location of point sources can be done with an accuracy better than this but this depends on the strength of the source
20. 0 1018 are pseudo detector numbers for the events with PSD flag 0 i e localized events 123 141 1100 1118 are pseudo detector numbers for the events with PSD flag 1 i e events with energy deposits at different locations in the detector 8 2 Build Observational Group og_create The first step for the Scientific Analysis of the SPI data is the creation of the observation group OG This task is fulfilled by the program og create which produces an observational group of PRP level out of an index of science windows groups or a list of SWG DOLs Figure 14 gives an example of such a list written to the ASCII file dols txt dols txt scw 0002 000200000022 000 swg prp fits 1 scw 0002 000200000032 000 swg_prp fits 1 scw 0002 000200000042 000 swg prp fits 1 scw 0002 000200000082 000 swg prp fits 1 scw 0003 000200000012 000 swg prp fits 1 scw 0003 000200000032 000 swg prp fits 1 scw 0004 000200000042 000 swg prp fits 1 scw 0004 000200000082 000 swg prp fits 1 Figure 14 example of a input list of SWG DOLs for og create og create also creates the standard obs branch of the directory tree where the following analysis will be performed and the high level science window groups will be produced To run this program you should specify the following parameters Description Parameters defining the name contents and location of the OG idxSwg string Index of science window group or ASCII
21. BGO shield 80 keV shield threshold without PSD Fluxes in cts cm s 5 1 3 Background Gamma Ray Lines Background gamma ray lines are emitted in passive materials close to the detectors and in the detector material itself Primary and secondary cosmic ray particles protons and neutrons induce excited nuclei in nuclear reactions with nuclei of the passive material The prompt or delayed radioactive de excitation of these nuclei leads to gamma ray lines which can be detected by the germanium detectors Calculations show that lines originating in the mask should not pose a problem for SPI 5 2 Instrumental Characterization and Calibration The SPI instrument has been fully tested and calibrated on ground before the launch Some tests and calibrations with radioactive sources were performed on ground with the full satellite The ISDC SPI Analysis User Manual Issue 0 9d1 12 sensitivities resolution and other characteristics given in this document are the result of testing of parts of the instrument testing of preliminary models of the instrument and careful model calculations They represent the current best knowledge of the SPI instrumental characterization After launch the SPI team will check that the prelaunch calibration as established on ground is maintained This is done during the initial in orbit phase Commissioning Phase Several observa tions are planned to check the imaging performance spectroscopic performance ba
22. DTI tpl out og dol string Input Output Observation Group DOL e g og spi fits GROUPING deadtimecorrection real fraction of livetime of the instrument for all pseudo detectors If this parameter is set to a value gt 0 0 then this is used as a fixed dead time correction value e g 0 98 for 9896 of the time the detector was alive If this parameter is 0 0 the correct dead times are determined automatically from the housekeeping data If this parameter is 1 the dead time is only determined for one detector correctly and this value is used for all detectors e g 0 98 Input in case you want to run a spidead for one science window only swg index dol corrected swg index DOL gti dol Good Time Interval DOL Additional parameters ISDC SPI Analysis User Manual Issue 0 9d1 32 clobber boolean Defaults to yes Lets you overwrite the GTI structure chatter integer Chatter Level varies from 1 to 100 Choose a higher chatter level for more logbook information e g 20 Created file spi dead_time fits contains the data structure SPI OBS DTI This data structure is a FITS table with two columns DEADRATIO and LIVETIME The DEADRATIO is a fraction of time during which the detectors are alive The relation between ONTIME DEADRATIO and LIVETIME is as follow LIVETIME DEADRATIO ONTIME The schematic representation of this data structure can be found in Figure 15 8 7 Energy Bin Definition spibounds T
23. Dithering Sensitivity Degradation The instrumental sensitivities given in Table 4 and Figures 6 7 are for a source on axis and do not take into account dithering As stated earlier observations with SPI should not be done in staring mode since this makes the identification and removal of the background impossible Dithering on the other hand has the disadvantage that the source is not observed for the full integration time in the center of the fully coded filed of view center of the instrument response The SPI response falls off towards the edge of the filed of view and therefore dithering will degrade the sensitivity of the instrument somewhat The hexagonal dither a central pointing with six surrounding pointings in hexagonal pattern all 2 apart only samples the central part of the SPI fully coded field of view Therefore no reduction in the sensitivity is noticeable The 5 by 5 dither a square pattern of 5 by 5 pointings around the source all with 2 spacing however samples closer to the edge of the fully coded field of view In this case the sensitivity is degraded by a factor 0 8374 i e the sensitivities given in Table 4 should be divided by this number to get the effective sensitivity 5 3 5 Detection of off axis sources The wide field of view of SPI allows the detection of off axis sources However it also means that off axis sources will create a shadowgram on the detector that increases the background photons for the prime targe
24. IN Pointing Definition Defines a number of time periods during which the S C attitude can be considered as constant for SPI analysis e g a slew can be splited into a number of periods and extracts the space craft attitude information from the input group Store the results in a pointing file for further use spipoint GTI Good Time Handling Generates selects and merges Good Time Intervals to produce a unique GTI which is to be used for selecting good events The ON_TIME i e the total net observation time within the good times in seconds is also computed Different GTIs can be derived for different detectors Therefore at this level user must define the list of detector to be used in the analysis and subsequent tasks spidead spiback spihist must read the detector list from the GTI table Detectors are defined according to the pseudo detector scheme spi_gti_creation DEAD Dead and Live Times ISDC SPI Analysis User Manual Issue 0 9d1 20 Build Observation Group Observation Group of Prepared Data Resulting Data Structures added to the Observation Group o Calibration Index coo IBIN Energy Bin Definition Scientific Analysis Preparation Event Binning Corrected_Data Pointings GTI Dead_Time Ebounds Imaging Analysis IBKG Background Generation ISRC Source Selection IRF ISRC Image Response Derivation IMAG Image Reconstruction gt
25. ISD AS oa ISDC SPIAUN p JU SPI Analysis User Manual INTEGRAL Science Data Centre SPI ANALYSIS USER MANUAL Reference ISDC SPIAUM Issue 0 9d1 Date 23 August 2002 INTEGRAL Science Data Centre Chemin d cogia 16 CH 1290 Versoix Switzerland http isdc unige ch Authors and Approvals lt ISDC SPI Analysis User Manual ASS 0 9d1 First Release at ISDC Prepared by M Chernyakova QA checked by iz a A A ieee Pe eed a bea aa ala Agreed Dyz CR ANA EE Ee da Approved BY RR AAA A A n Ee ub ee dei ISDC SPI Analysis User Manual Issue 0 9d1 i Document Status Sheet SPI Analysis User Manual PS 26 AUG 2002 ISDC SPI Analysis User Manual Issue 0 9d1 ii Contents Acronyms and Abbreviations vi I Instrument Definition 1 1 Scientific Performances Summary 2 2 Instrument Description 3 2I The Overall Designzz are ee Bok wee ok ght e ot da e ta e a Boe pays d h 3 2 2 The Passive Mask to dg a etete es eiui tobe heey BOE ood Bee Ee 3 2 3 THe Cam ras Xp OO eS A EEE Se eee ew 4 2 9 OFVOSUAU he onerare Seid aaa ee Be Ee NS te Ca A AA O OU e 4 2 3 2 Detectors and Pre Amplifiers 22e 5 2 3 3 The Detector Electronics en 5 2 3 4 Pulse Shape Discriminator PSD o ooo o 5 2 4 Anti Coincidence Subassembly ACS o o 6 2 5 The Plastic Scintillator Anti Coincidence Subassembly PSAC 6 2 6 Electronics uk EA Pe
26. If there is no example after the parameter description then you should enter instead of the Value 8 1 Pseudo detectors Definition In image reconstruction and spectral extraction processes PSD events and multi detector events are binned into a number of pseudo detectors Thus the different kinds of events are treated as being detected by other than the physical detectors This allows to treat them independently for example each pseudo detector has an individual response function dead time and so on Pseudo detector numbers are defined as follow Table 7 Pseudo Detector Pseudo Detector Description Number ID 0 18 0 18 numbers for the single and the PSD any flag events 19 60 20001 21718 pseudo detectors for the double events The first digit of the ID indicating the multiplicity i e 2 is followed by four digits two for each detector numbers E g double events which hit detectors 4 and 15 are binned into pseudo detector number 20415 61 84 3000102 3061718 are pseudo detectors for the triple events The first digit of the ID indicating the multiplicity i e 3 is followed by six digits two for each detector numbers E g triple events which hit detectors 0 13 and 6 are binned into pseudo detector number 3001306 85 103 1900 1918 are pseudo detector numbers for the single events exclud ing PSD events ISDC SPI Analysis User Manual Issue 0 9d1 28 104 122 100
27. SPI OSGL RAW SPI OPSD RAW SPI OCRV RAW SPI OME2 RAW SPI OME3 RAW SPI OME4 RAW SPI OME5 RAW SPI OMEH RAW SPI OMP3 RAW SPI OMP4 RAW SPI OMP5 RAW SPI OMP6 RAW SPI OMPH RAW SPI OPPS RAW spi_prp_oper fits Prepared Data Structure SPI OSGL PRP SPI OPSD PRP SPI OCRV PRP SPI OME2 PRP SPI OME3 PRP SPI OME4 PRP SPI OME5 PRP SPI OMEH PRP SPI OMP3 PRP SPI OMP4 PRP SPI OMP5 PRP SPI OMP6 PRP SPI OMPH PRP SPI OPPS PRP spi_cor_oper fits Corrected Data Structure SPI OSGL COR SPI OPSD COR SPI OCRV COR SPI OME2 COR SPI OME3 COR SPI OME4 COR SPI OME5 COR SPI OMEH COR SPI OMP3 COR SPI OMP4 COR SPI OMP5 COR SPI OMP6 COR SPI OMPH COR SPI OPPS COR in Table 6 The information about the multiple events processed by PSD is added to the multiple event data structure as well as to the multiple event processed by PSD data structure so that the last one contains redundant information and is not used for the scientific processing of the data The data structure for pure PSD events and the one with examples of the PSD curves for the random events are also used for internal purposes only All raw event data structures used for scientific analyses are binary tables which contain such event information as the time tag local SPI time of the event number and channel of detectors hit in the table this columns are labeled TIME_TAG DETE and PHA correspondingly The data structures for the multiple events contain also the information a
28. ain_coeff fits SPI COEF CAL outfile Output file optional in case the input OG SWG should not be modified Additional parameters Decides if existing output data are to be overwritten or not The result of the correction is written to the file spi_cor oper fits in the scw directory structure This file like the file with raw and prepared data contains 14 substructures one per event type listed in the table 6 All these data structures contain the information about the event energy in keV column ENERGY 8 4 Pointing Definition spipoint The executable spipoint defines time intervals with stable enough attitude during the observation Stable means that the attitude did not vary more than a tolerance value given as an input pa rameter In a first approximation the periods of stable attitude during an observation are the ISDC pointing science windows but their exact boundaries will depend on the specified attitude ISDC SPI Analysis User Manual Issue 0 9d1 30 tolerance The slew can also be divided into a number of relatively small intervals during which the attitude is stable within the given tolerance Input Output rogroup string DOL of the read only group for input rwgroup string DOL of the read write group for input and output e g og_spi fits GROUPING pointing_dol string output pointing data structure e g pointings fits SPI OBS PNT tpl Stability parameters Tolerance on the stabili
29. ation Group ARF Ancillary Response Files PHA Pulse Height Amplifier BGO Bismuth Germanate PI Pulse Tisdssnt DFEE Digital Front End Electronics y PSA Pulse Shape Amplifier DOL Data Object Locator i PSAC Plastic Scintillator Anti Coincidence DPE Data Processing Electronics Subassembly DS Data Structure PSD Pulse Shape Discriminator System FCFOV Fully Coded Field of View f RMF Redistribution Matrix Files FOV Field of View FWHM Full Width at Half Maximum PON PEIUS Window GRB Gamma Ray Burst SWG Science Window Group GTI Good Time Interval TBW To be written IC Instrument Characteristics TM Telemetry IRF Image Responce File UTC Coordinated Universal Time ISDC SPI Analysis User Manual Issue 0 9d1 vi Part I Instrument Definition ISDC SPI Analysis User Manual Issue 0 9d1 1 Scientific Performances Summary The spectrometer SPI SPectrometer on INTEGRAL performs spectral analysis of gamma ray point sources and extended regions in the 20 keV 8 MeV energy range The main characteristics of the instrument are given in Table 1 Table 1 Main characteristics of the SPI instrument Mask dimensions 665 mm flat to flat 30 mm thick Tungsten Detector unit Encapsulated Ge hexagonal geometry 19 detectors 70 mm thick Energy range 20 keV 8 MeV Energy resolution FWHM 2 2 keV at 1 33 MeV for each detector 3 keV for the whole spectrometer Angular resolution 2 5 for point sources Point source positioning lt 1
30. ble together The size of the detectors is 5 6 cm flat to flat with a height of 7 cm The cold plate is made of beryllium and it is directly cooled by the SPI cooling system The bottom of the cold plate is hollowed to mount the printed board pre amplifiers PA 1 cold electronics The PA 1 electronics include the high voltage filter and the connection between the detector and the Charge Sensitive Amplifier CSA A second set of 19 pre amplifiers PA 2 is mounted on a second cold plate beryllium at 210 K The PA 2 is connected to the PA 1 with a cryogenic cable The hexagonal detectors are mounted with minimum space between them such that the axes of two adjacent detectors are 6 cm apart The material in front of the detector has good transparency for gamma rays at 20 keV To cure the degeneration of the Ge detectors an annealing operation should be done every 6 to 12 months strongly dependent on the high energy neutron flux at the satellite position in which the detectors are heated to 105 degrees C The instrument will not be available for scientific observations during the time needed for the annealing operation and the cooling phase afterwards in total approximately 200 hours 2 3 3 The Detector Electronics The signals from the pre amplifiers are sent to the amplification chain which is made up of a Pulse Shape Amplifier PSA and a Pulse Height Amplifier PHA The PSA amplifies the pulses such that the performance of the spectrometer
31. bout the multiplicity of the event and the time delay between the detectors columns MULT and DELTA TIME The data structure for PSD event additionally contains the column with PSD flag it is equal to 0 for localized events and to 1 for unlocalized events and the compressed PSD data columns PSD RAWFLAG and PSD DATA 7 3 Prepared Data The main task of the Science Window Pipeline is to prepare raw data for the following Scientific Analysis It converts the HK parameters into the physical units and makes some corrections and transformations of the raw data that are not included in Pre Processing because they involve alteration of data format or use additional parameters that do not come from the telemetry data flow As a result the file spi prp oper fits is created This file like the file with raw data also contains 14 substructures listed in the Table 6 All these data structures are binary tables with the absolute time information column OB TIME The data structure for PSD events also contains the unpacked PSD information about the form of the pulse shape the flag equal to 0 in case if the PSD analysis were done without internal errors the positions of the two highest peaks of the pulse curve and the ratio of their amplitudes columns PSD ERR PSD_TTP1 PSD_TTP2 and PSD_AMP The data structures for multiple events besides the time information contain column with the information about the event true multiplicity column MULT FLAG
32. c illustration of the three RMF types RMFs EBOUNDS O Vl CS amp S e Y SSES OS S EE S S pe qs7 A 153 qw 9 sae A ee puse p ree poem Er E SS a MaS eus sace ee gee S er E 1E 1E nl nI nl nE keV keV keV keV SPL RMFI RSP SPL EBDS RSP SPI RMF2 RSP SPI RMF3 RSP spi_rmf_reponse fits Figure 12 Format of the RMF file IRF data structures In the case of the instrumental response for image reconstruction a complete set of ARFs coeffi cients for a given photon energy Ep is stored as a 4 dimensional image called an Image Response File IRF in a SPL IRF RSP data structure An IRF image has 1 a detector axis 2 a zenith equidistant FOV X axis 3 a zenith equidistant FOV Y axis and 4 an axis to store the three types of ARF In addition IRFs for several independent regions are derived and stored in different data struc tures This is to allow for different bin sizes for different regions For example in the current implementation the bin size in x y in the Field Of View FOV is thinner than the one outside the FOV An index SPI IRF RSP IDX links a complete set of IRFs i e a 2 D grid for a complete set of photon energies and region numbers while a group relates the index to the corresponding three RMFs ARF and RMF for spectral analysis with XSPEC In the case of spectral analysis only the instrumental response for a few positions in the sky the positions
33. ce Subassembly ACS The main function of the Anti Coincidence Subassembly ACS is to shield the Ge detectors against background photons and particles from sources outside the field of view The ACS system con sists of 91 Bismuth Germanate BGO scintillator crystals in combination with photo multiplier tubes The BGO crystal thickness has been optimized with Monte Carlo simulations to minimize the detector background by minimizing the shield leakage and neutron induced radiation in the BGO The BGO shield for the side and the rear of the camera is 5 cm thick The complete shield consists of two collimator rings that define the SPI field of view located between the mask and the camera unit a side shield and a rear shield that surround the camera The BGO scintillator crystals are used to convert all incoming events into photons in the 480 nm region visible light Photo multiplier tubes are used to detect these photons and convert them into electrical pulses which are sorted normalized and summed up by the ACS electronics Each photon induces a time tagged veto signal The ACS output data is directed to the Digital Front End Electronics DFEE which formats the data and time tags each event Photons that are not in coincidence with an ACS veto event are considered good The ACS off photons i e all photons that are detected by the Ge detectors independent of the veto status are integrated into background spectra that are sent to the ground eve
34. ck sin amp real this parameter specifies the amplitude of the SIN background component cnts det sec kev back cos amp real this parameter specifies the amplitude of the COS background component cnts det sec kev general background model back model gen if you want a general background component you should enter YES otherwise NO e g NO back model comp 1 for the general background model you should enter it s name or identifier The produced SPI BMOD DSP in the file spi back_model fits contains model background rates column COUNTS for a particular detector and a given SPI pointing The size of the vector column is equal to the number of energy bins considered The schematic representation of the SPI BMOD DSP data structure can be found in Figure 15 ISDC SPI Analysis User Manual Issue 0 9d1 38 EBOUNDS Energy Bin Boundaries POINTING Observation Attitude energy_boundaries fits pointings fits 1 0 2 1 2 2 1U 1B 1U 1E 1E SPL EBDS SET 1E deg 1D 1E 1E 1E deg deg deg s 15A 4U 4U ID ID d d SA DETE SPECTRA BACKGROUND ARF RESPONSE DEAD TIME SPI GTI SPL OBS PNT 103 0 1 103 2 1 2 1 24 sunulog MOS Figure 15 Analysis Auxiliary Data and Intermediate Level Data ISDC SPI A
35. ckground flux calibration sensitivity and the sensitivity to out of field sources If any large changes are found especially in the sensitivities observers will be informed Currently calibration observations of the Crab nebula and Cygnus X 1 are foreseen to provide the calibration that will be used for the data processing Unfortunately the Crab nebula is not visible to INTEGRAL so only Cygnus X 1 can be observed during the Commissioning Phase The Crab nebula will however be observed as soon as it becomes available It is expected that the observation of Cygnus X 1 will provide an accurate calibration up to about 2 MeV whereas the Crab nebula is needed to extend the calibration to higher energies Currently the following observations of these targets are foreseen e Cygnus X 1 5 by 5 dithers on source and two pointings 10 degrees off source for 2 7 10 seconds each hexagonal dither with source on axis for 2 10 seconds e Crab 5 by 5 dither centered on the source for 1 8x 10 seconds hexagonal dither centered on the source for 1 26x 10 seconds In Table 3 the expected accuracy for the hexagonal dithering observation of both sources for several energy bands in the range of the SPI instrument is given Back gomd Fx s Pix o 25 so 519107 921 10 5 099 351 10 7 30 50 so 15219077 201105038 13010 7 14 Table 3 Accuracy for calibration observations of Cygnus X 1 and the Crab nebula
36. cw 0087 008700070010 000 swg_prp fits 1 scw 0087 008700080010 000 swg_prp fits 1 To create an observation group with the name obs_id give the following command og_create idxSwg dols txt ogid obs_id baseDir instrument SPI This command also creates a new directory obs obs_id where the following analysis will take place Go to your new obs branch cd obs obs_id Now you are ready to start the scientific analysis of your data ISDC SPI Analysis User Manual Issue 0 9d1 51 9 2 Example 1 image of the 511 keV line reference orbit test source To run the script type spi_osa After the launch of the GUI you will see the following picture ISDCTaskGUI Version 0 1 obs group og_spi fits GROUPING endLevel IMA run spiskymax run spiros spi ati creation det id 0 84 Figure 16 screenshot of the spi_osa script GUI Blue lines described the parameters you have to enter To see the hidden parameters mark the box Show hidden parameters For this example enter the following values Specific Script Parameters For levels definition see e g section 6 startLevel COR endLevel IMA run spiskymax YES run spiros YES Parameters forspi_gti_creation ISDC SPI Analysis User Manual Issue 0 9d1 52 Parameters for spibounds spibounds_nregions 1 spibounds regions 500 520 spibounds nbins 1 spiros_image fov POINTING FCFOV spiros_mode IMAGING spiskymax_image fov POINTING FCFOV spisk
37. e is the index file and the second one contains the light curve for all sources found The data structure SPI SRC LCR have the following columns Column name Description PTID_SPI ID of the SPI pointing defined for this flux value OB_TIME OBT at the middle of the SPI pointing TIME Time at the middle of the SPI pointing in ISDC JD E_MIN Minimum energy of the energy bin E_MAX Maximum energy of the energy bin E_MEAN Mean energy of the energy bin FLUX Flux of the source STAT_ERR Statistical error of the flux SYS_ERR Systematic error of the flux QUALITY Quality flags for the energy bins ISDC SPI Analysis User Manual Issue 0 9d1 46 8 11 Image Reconstruction spiskymax The detailed description of spiskymaz is given in the document written by its author A Strong MPE Garching The aim of spiskymaz is to generate images from SPI data SPI is a coded mask instrument so direct deconvolution is in principle possible but in practice the response is complex and the data include many pointing directions of the instrument so indirect imaging is essential Indirect imag ing implies forward folding for any candidate image we convolve with the instrument response function and compare the result with the observed data This gives the basis for any iterative method which seeks to successively improve the agreement of the predicted with the observed data by adjusting the image One approach is to regard the image as made up of
38. e strength probably too large of the source and then the detector counts expected from it e Subtract source counts from the input count data to create residue count data more or less due to other sources not yet located e With these residue counts the procedure above is repeated creating a new location image searching it for any new source and adding it to a growing list Each time a new source is added to the list all sources are allowed to float to more precise locations before their counts are subtracted from the input counts ISDC SPI Analysis User Manual Issue 0 9d1 40 IROS repeats the iterative procedure above locating each new source approximately always allowing them to float to more optimal locations creating new residue count data and stopping when nothing significant can be found This procedure can be repeated in any number of energy bins to calculate a mean location for each source over the entire spectrum range For the user running spiros in its IMAGING mode the main task is to get the appropriate binned count data output from spihist decide the size of the field of view they wish to search and how many sources they wish to look for The user may have an input catalogue of known sources to locate them again more precisely or find an extra one or two in addition or just to make an image of them The spiros parameters most important for the first try are the following Input Output spiros operation mode you can
39. edure which locates sources one by one from the strongest to the weakest there will be output of images at each search iteration showing the sources known or located and the emission residue remaining It is the residue image that SPIROS will search to see if there are any new sources to be found Possible values are Y and ENS e g Y Output image array parameters for IMAGING mode reference coord string Output image reference coordinate system This parameter will normally have the value of RADEC but if GALACTIC is specified the observation pointing directions and imaging frame of reference will be translated into l b galactic coordinates e g RADEC image fov string Extent and location of output image POINTING FCFOV will set the centrepoint of the image array to that of the observa tion field of view The size of the image field of view is extended by the FULLY CODED field of view of SPI about 8 e g POINTING FCFOV blur size real FWHM blurring for display of point sources It should be not too small or you may not immediate see point sources in the image e g 0 5 ISDC SPI Analysis User Manual Issue 0 9d1 42 Image proj real Output image projection type Possible values are CAR TAN and AIT e g CAR Source location parameters nofsources integer The maximum number of point sources spiros will search for unless a new source fa
40. em of SPI will detect gamma ray photons from a large part of the sky during all observations It can thus function as a gamma ray burst monitor Because of the size of the ACS BGO shield it has a high sensitivity for gamma ray bursts A sensitivity calculation shows that SPI will detect of the order of a few hundred gamma ray bursts per year minimal detectable energy flux between 4 x 1077 erg cm s and 7 x 107 erg cm s This is comparable to BATSE Unfortunately the ACS data cannot be directionally sensitive therefore accurate positions of gamma ray bursts that are detected with the ACS have to be determined through triangulation methods with other distant spacecraft e g Ulysses To accommodate these triangulations the acquisition of the veto count which is done every 50 ms has a timing error of about 2 5 ms The INTEGRAL Science Data Centre ISDC will check the stream of veto count rates automat ically If a gamma ray burst is detected sudden increase in the count rate over a short period of time an alert will be issued to the institutes that are doing the triangulation observations 4th Interplanetary Network From the accurate timings of the SPI detection and detections by other spacecraft a position will be constructed that is communicated to the world The accuracy that can be achieved with this method is much better than an arcminute due to the long baseline and the accurate timing of the SPI ACS events Note that the ACS
41. events are written to the instrument House Keeping and are therefore made public immediately Observers can be notified of these gamma ray burst events by subscribing to the gamma ray burst alert system of the INTEGRAL Science Data Centre GRBs can of course also be detected in the field of view of SPI using the normal photon by photon mode In this case the data belongs to the observer who has a accepted proposal for GRBs in the field of view ISDC SPI Analysis User Manual Issue 0 9d1 10 5 Performance of the Instrument 5 1 Components and Sources of Instrumental Background The SPI instrument is background limited The sensitivity of the instrument is therefore largely dependent on the background and on the correct identification of background photons The back ground can be divided into the following main components e continuum radiation e 511 keV line radiation e gamma ray lines 5 1 1 Continuum Background The continuum background can be split into several components depending on their origin First the radiation coming from outside the instrument This can be the cosmic diffuse gamma ray flux that comes in through the instrument aperture or leakage through the BGO shield of cosmic diffuse gamma ray radiation and gamma continuum radiation from the spacecraft induces by energetic cosmic ray particles Secondly scattering in the Ge detectors of neutrons that were produced in the spacecraft or other parts of the instrument Th
42. ew since probability for an chance n sigma excess due to noise somewhere in the map is higher 5 3 7 Timing Capabilities The instrument works in photon by photon mode Each photon data set includes timing informa tion given by a 100us clock signal This clock is synchronized to the on board clock and thus to the UTC The timing error budget for SPI is derived from e the accuracy of the on board clock and the synchronization e the conversion between on board time and UTC e the conversion between UTC arrival time at the spacecraft and the arrival time at the solar system barycentre The resulting SPI timing accuracy calculated in this way is 1291s 3c accuracy and a 90 confi dence accuracy of 94us ISDC SPI Analysis User Manual Issue 0 9d1 19 Part II Data Analysis 6 Overview Each photon that is absorbed in a SPI Ge detector gives a pulse that is sent to the electronics The electronics analyse the incoming pulses and the veto signals and tags each photon with the energy the time and the type of event i e single detector events with or without PSD and multiple detector events These data are then sent to the ground During the Pre Processing the information contained in the TM packets is written into a set of FITS formatted data files RAW data Pre Processing produces a set of RAW data files for each Science Window After the Pre Processing the Science Window Pipeline converts the local on board time LOBT
43. flux definition source_ON_radius_1 ON radius degrees e g 2 0 source_OFF_radius_1 OFF radius degrees e g 5 0 If you follow the naming scheme used in the provided parameter files then in the directory spi you find the following files after the run of spiskymaz skymax_index fits skymax_image fits ISDC SPI Analysis User Manual Issue 0 9d1 48 Spiskymax sources fits The first file skymax_index fits is an index file File skymax_image fits contains the image produced by spiskymaz File spiskymax_sources fits is a copy of the input catalog ISDC SPI Analysis User Manual Issue 0 9d1 49 9 Cookbook Now we will see how to analyze your data using the script combining all the executables described above Make sure to use a sufficient machine e g isdcull0 isdcull9 crab etc at ISDC 9 1 Preparation During the software installation the environment is settled automatically At ISDC you should do it manually to make sure you have the latest software version At the moment there are two possibilities of setting the environment The first one is general for all the 4 instruments but is not fully tested yet So if you have problems with it send an e mail to Bruce bruce oneel obs unige ch Thus you will help us to make it working properly In any case the second variant should work for sure So type either source isdc scripts login ISDC_ENV isdc integration osa_int current ROOTSYS isdc_soft_platform roo
44. from the pointing definition e g indef outputformat The available output file formats are ISDC in which case an ISDC table will be produced or PHA in which case a PHA II data structure will be at the output e g ISDC In the file spi evts_det_spec fits the data structure SPI OBS DSP contains binned SPI events in the form of detector spectra One row of this FITS table contains an event spectrum column COUNTS and a column STAT ERR for statistical errors integrated for a particular detector and a given SPI pointing The length of the vector column is equal to the number of energy bin considered The lower and upper energy boundaries for each bin themselves are stored in the SPI EBDS SET data structure produced by the spibounds The schematic representation of the SPI OBS DSP data structure can be found in Figure 15 8 9 SPI Background Generation spiback spiback produces background models for imaging and spectral analysis The simplest case is to assume a background that does not change with time The background have then only one free parameter per detector in the image analysis The goal of the background generation is to provide a model for the time and energy variations in order to limit the number of background parameters in a more realistic imaging solution For example one can assume that the background follows the time variation of the total number of Anti Coincidence Shield ACS counts and then solve f
45. h will not be changed by spiros otherwise they will be flagged as VARIABLE and their locations will be allowed to shift to a more optimum loca tion when new sources are located e g 0 1 ISDC SPI Analysis User Manual Issue 0 9d1 41 Output catalogue and image files for IMAGING mode source res DOL of the output source catalogue with all known and any new located sources e g spi source_res fits SPI SRCL RES tpl image idx Name of the output sky image index e g spi spiros image index fits SPI SK Y IMA IDX tpl image inst This parameter indicates if source flux intensity images are re quired for output Possible values are Y N or the image name If only Y is entered for the output dataset name will be made from the image index file name with X intensity appended to it e g Y image err This parameter indicates if source flux error maps are required for output Possible values are Y N or the image name If only Y is entered for the output dataset name will be made from the image index file name with error appended to it e g Y image sig This parameter indicates if source flux sigma maps are required for output Possible values are Y N or the image name If only Y is entered for the output dataset name will be made from the image index file name with sigma appended to it e g ey iteration output This parameter indicates that in the search proc
46. he energy binning nregions integer Number of regions in energy space for which distinct bin ning algorithms are to be defined e g 3 regions The boundaries of the energy regions separated by com mas e g 1325 1340 1165 1180 The number of bins per region separated by commas Neg ative numbers indicate logarithmically space bins e g 15 3 15 bintype The type of bin boundaries to construct photon PT de tector pulse_height PHA Default is photon you can also define energy binning from file Optional input file containing energy bin boundary defini tions Additional parameters clobber boolean Defaults to yes Option to whether overwrite existing files or not chatter integer Chatter Level varies from 1 to 100 Default level is 20 telescope string Telescope name Default is INTEGRAL instrume string Instrument name e g SPI In the energy boundary file spi energy_boundaries fits the energy channels can either be de fined in energy units with E_MIN and E MAX or in instrumental channel units with PHA_MIN PHA_MAX and E RANGE E RANGE specifies SPI energy range 0 low PHA 16384 to 32767 1 high PHA 49152 to 65535 In physical units low range approximately corresponds to energies less then 2MeV and high range to the higher ones The schematic representation of the SPI EBDS SET data structure can be found in Figure 15 8 8 SPI Events Binning spihist spthi
47. he executable spibounds is used to construct energy boundaries to be used for the binning of SPI event data Options include uniform linear or logarithmic spacing as well as superimposing sub regions e g of finer spacing over a global binning scheme so that you can investigate more carefully particular spectral regions e g for spectral regions likely to contain line emission Input Output in og dol DOL of the input fits file which identifies the observation group to be processed energy boundaries dol Output FITS table written to the output observation group containing the energy bin boundaries specified by the user e g spi energy boundaries fits SPI EBDS SET tpl out og dol DOL of the output observation group e g og_spi fits GROUPING You can specify the output file The name of the output file with the bin boundaries in case you want to run spibounds for specific science windows swg index dol string DOL of the input FITS file containing the index of science windows to be analyzed gti dol string DOL of the input FITS file containing the list of good time intervals for each detector and pointing deadtime dol string DOL of the input FITS file containing the list of deadtime correction factors and livetimes for each detector and point ing ISDC SPI Analysis User Manual Issue 0 9d1 33 ebounds dol string DOL of the FITS table containing the energy bin bound aries parameters to define t
48. ifier Modified Julian Date of source s first identification One commonly used name for the source source classification code Source right ascension in degrees Source declination in degrees Error radius Relative distance of the source d r1 r2 where d dis tance to catalog source identified with the source and rn are the respective error radii of the sources Model for source spatial extension point disk ellipse square gaussian Bspline etc Number of parameters for source spatial extension Parameters for source spatial extension Model for source spectrum XSPEC syntax Number of parameters for source spectrum Parameters for source spectrum Model for source intensity variability const sin burst Number of parameters for source intensity variability Parameters for source intensity variability Comments SPI flux in the soft SPI energy band lt 2MeV according to input catalogue SPI flux in the hard SPI energy band gt 2MeV according to input catalogue ISGRI flux in the soft ISGRI energy band according to input catalogue ISGRI flux in the hard ISGRI energy band according to input catalogue PICsIT flux in the soft PICsIT energy band according to input catalogue PICsIT flux in the hard PICsIT energy band according to input catalogue JEMX flux in the soft JEMX energy band according to input catalogue JEMX flux in the hard JEMX energy ban according to input catalogued Lower energy boundaries vec
49. ion of the positrons resulting from pair creation can also produce other interactions or escape the detector In SPI the detector array is used to recover the total energy of an incoming photon This contributes to raise the full energy peak and to reduce the Compton continuum Unfortunately it also degrades spatial information as it is not possible in general to determine which detector was hit first All the signal output data produced from the detection plane are also directed towards PSD which by analysis of the signal shape is able to minimize the background in the range 200 keV 2 MeV By comparing the form of impulsions produced by the pre amplifiers of the detectors with the profiles archived in a library the PSD system determines whether the measured shape is best represented by a single or multiple shapes and consequently whether the signal was localized or not This classification allows an effective rejection of background events that arise from localized beta decays within the SPI Germanium detectors During the detector life its characteristics could change and consequently the shapes of the events evolve This is the reason why the shapes must be analyzed continuously The shapes evolution could lead to build a new reference shapes library From time to time it is necessary to have a large selection of samples One curve is downloaded each 4 seconds Several thousands of simple pulses per detector are necessary for checking or reb
50. irdly background components produced inside the spectrometer detectors These consist of localized G decays non localized decays and BFdecays About 9096 of localized 87 decays single events are identified by the pulse shape discriminator system The non localized 8 decays multiple interactions in the detector e g Compton scattering and photoelectric interaction are more difficult to identify since in this case the electron and the gamma photon are emitted simultaneously therefore the resulting pulse looks like a normal source event for the PSD The continuum emission from the mask and the BGO emission when the veto electronics are blacked out veto dead time are negligible The individual components and the total continuum background emission are illustrated in Figure 3 5 1 2 511 keV Background The 511 keV background can be split into five components e the continuum background under the 511 keV line This component is estimated from the continuum background spectrum as explained above e passive material 511 keV photons from passive material due to Bt decays of unstable nuclei in these materials These unstable nuclei are formed due to interactions of protons and neutrons that are produced in interactions of cosmic ray particles with the detectors shield or cryostat The unstable nuclei decay through 8 decay The annihilation of the positron leads to the emission of two 511 keV photons in opposite directions If one is absorbed b
51. is You should just set parameters in the parameter file spi osa par and run the script spi_osa We will speak about the script a little bit later in the cookbook chapter at first we want to present you the decomposition of the script in order to explain how it works and what parameters you are to enter There are several ways of entering the parameters you can modify the parameter file itself the explanation of what is the parameter file can be found in the 1 Section Software Tools you can find all the parameter files in the directory pfiles input them from the command line or use a Graphical User Interface GUI From the command line you should enter those parameters that are not defined as hidden in the parameter file see below With a GUI you can see all parameters when you select an option Show hidden parameters Most of the executables described below have different set of parameters you can use them in a pipeline as it is done in the script or separately If you specify an observation group as input parameter then the program works with all the science windows members of the group As an output executables can either produce new files and groups or modify the existing ones If the input observation group is not specified then the output observation group is also taken as an input one Describing the executables we give as an example set of the parameters that will allow you to perform a first try of data analysis
52. le are 3 sigma in 10 seconds pure integration time using a BGO threshold of 80 keV a plastic scintillator threshold of 300 keV and with PSD and multiple event reduction techniques applied this is similar to the normal operating mode The continuum sensitivities are for AE E 2 and are calculated from the narrow line sensitivity by dividing those by VR AE where R is the instrument resolution for lines The line sensitivities are fluxes in photons cm s the continuum sensitivities are ISDC SPI Analysis User Manual Issue 0 9d1 14 T T T T proto 0 resolution o sL ESSI ES 2104 11 7 FWHM keV 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Energy ke Figure 5 The measured energy resolution of an individual SPI detector This was measured using lab oratory detectors The resolution of the full instrument with all 19 detectors is slightly lower than this fluxes in photons cm 7 s keV The line sensitivities are for narrow lines For broad lines the sensitivity of the instrument degrades as can be seen in Figure 8 where the factor is plotted with which the sensitivity is degraded as function of the energy for three line widths 1 3 and 10 of the energy of the line Note that the sensitivity for 511 keV is not given in Figure 7 but only in Table 4 The 511 keV sensitivity is worse than the surrounding continuum due to the strong 511 keV background line originating in the instrument 5 3 4
53. lls below the sigma threshold given by parameter sigmathres in which case it will stop searching e g 1 sigmathres The sigma threshold to reject new sources located and stop searching for anymore e g 3 0 kofsources Shape of sources to be searched for POINT prompts a search for as many point sources as given by parameter nofsources e g POINT srclocbins With this parameter the user can try a one step approach by binning count data only once in the large number of energy bins required for spectra then using this parameter to select a smaller subset of bins for source location ALL will locate sources in each energy bin of the input count spectrum and form a sigma weighted mean value to output in the result images SUM will locate sources in one energy bin covering the input energy spectrum e g SUM Control of source flux location and width optimization optistat string For the count values expected from SPI exposures the noise or statistics in them can generally be expected to be Gaussian requiring the minimization of a x statistic In some cases es pecially of weak diffuse emission the count noise can be expected to be Poisson requiring the minimization of a Maximum Likeli hood parameter such as the Cash statistic The possible values of the parameter are CHI2 LIKER e g CHI2 maxlikprec real This is the stopping criteria in optimizing a x or ML statistic and is used in conjunc
54. me signal counts etc The detected events are time tagged with a 20 MHz local clock which provides the timing resolution The reset timing reference is done with the 8 Hz satellite clock The DFEE uses the 125 ms time frames to analyze and process the input information and pass it on to the DPE The statistics are passed on to the DPE every second The DPE is the interface to the instrument It is part of the On Board Data Handling OBDH unit It provides the telecommand and telemetry interfaces to the instrument and it provides the environment for the instrument dedicated software Instrument Application Software IASW ISDC SPI Analysis User Manual Issue 0 9d1 6 3 Instrument Operations 3 1 How the instrument works The SPI instrument provides a combination of high resolution spectroscopy with imaging capabil ities The performance characteristics of the instrument each depend on one of the instrumental subsystems e Energy resolution is determined by the cooled Ge detectors e Angular resolution is determined by the pixel size of the mask and the detector and the distance between them However imaging with SPI requires a special operation dither since a single pointing does not unambiguously define a sky image For this the 5 by 5 and hexagonal dithers have to be used see below e Field of View determined by the area of the mask and the detector and the distance between them as well as the ACS shield e Sensitivity
55. n for pointed observations is very difficult if not impossible due to background inhomogeneity over the detector plane 4 2 Imaging The imaging performance of SPI depends also on the dithering pattern that is used In general the greater the number of pointings the better the imaging Calculations were done to estimate the imaging performance of the instrument using simple correlation mapping More sophisticated techniques may be used to reduce or remove artifacts present in such images but this can only be done at the expense of worsening the signal to noise ratio or worsening correlations between parts of the image In these calculations the background in each detector at each energy is assumed to be constant but different between detectors The calculations show that when using the hexagonal dither pattern the reconstructed point source response function shows very strong side lobes at distances of 10 to 20 from the center Therefore this mode should only be used for isolated point sources and is not really suitable for imaging The side lobes are still present but significantly less ISDC SPI Analysis User Manual Issue 0 9d1 9 with the 5 by 5 dither pattern about 50 of the hexagonal case To remove these side lobes which will cause artifacts in reconstructed images the only possibility is to enlarge the imaged area by observing multiple pointings i e multiple dither patterns 4 3 Gamma ray Burst Detection The ACS syst
56. n of energy reduction factor for the sensitivity for hexagonal and 5 by 5 dithers in Table 5 The reduction for staring is similar to the one for hexagonal dithers Observers can calculate the effective sensitivity by dividing the sensitivity limits given in Table 4 by the factor given in Table 5 Off axis distance degrees NEC M 23 id 5 00 99148 00 99 Table 5 Sensitivity degradation factor as function of the distance off axis for a hexagonal and a 5 by 5 dither pattern 5 3 6 Imaging Capabilities The values presented in Table 4 are for an identified point source i e a 30 excess in a pixel However for unknown sources in an image of an area of sky the situation is slightly different In a map containing a large number of pixels the probability that an n sigma excess will occur by chance somewhere in the map can be significantly higher than suggested by the integral error function In a SPI map covering say 25x25 degrees there are approximately 60 independent ISDC SPI Analysis User Manual Issue 0 9d1 18 pixels Thus 99 confidence that a source at a specific position a known source is real requires 2 35 sigma whereas 99 confidence that a source found at an arbitrary position somewhere in the field an new unknown source is real requires 3 6 sigma significance Therefore to identify new unknown sources in the field of view a higher significance is required than for an unknown source in the field of vi
57. n the detector Ep Energy of photons X degree Figure 10 Some definitions used in the response description In order to reduce their size and to speed up the processing the response matrices are decomposed into two sets of files the ancillary response files ARFs and the redistribution matrix files RMFs following the XSPEC paradigm The ARFs describe the geometrical factors with effective areas in cm per input photon energy Ep bin The RMF are decomposed into three categories as illustrated in Fig 11 A first RMF described the full energy peak a second the Compton continuum with the events interacting first in the detectors and a third the Compton continuum with the event interacting first in the passive material inside the shield These RMFs are to a good approximation independent of detector and direction Three corresponding ARF sets are defined and the final response is a linear combination of the AFR and the RMF coefficients RMF file spi_ rmf_response fits contains data structures for each kind of RMF and an EBOUNDS extension as it is shown in Figure 12 The columns N_GRP F_CHAN and N_CHAN are used for a simple compression scheme which alleviates the necessity of storing redundant zero value elements and which can be understood with a glance at Fig 13 LO_THRES is stored as a keyword in the RMF data structure ISDC SPI Analysis User Manual Issue 0 9d1 25 For a given Ep Ne Ec Figure 11 Schemati
58. nalysis User Manual Issue 0 9d1 nE nE nE nE Counts nE nV Counts 1D s 1E 1D nU nD nD d d s nU 1V ISA SPI ARF RSP resp_arf fits 2 ae ag S a amp 4 ag 2 DN 3 Q a 2 nn amp ul V AS OQ Ana nu un Ed 28 e Qu Hes d Q vi a2 Qu ES nm oN 39 8 10 Source Reconstruction and Spectra Extraction spiros The detailed description of spiros is given in the document written by its author P H Connell University of Birmingham Here we give a brief explanation of the program and describe only the most important parameters for a first try Note that even for the explained parameters we don t give the full range of possible values The primary purpose of spiros is to use SPI data to locate point or pointlike sources in the observation field of view and to output a catalogue of their parameters along with images their spectra and any flux variability in time spiros has three basic operating modes to choose from e IMAGING mode Here the aim is only to locate point or pointlike sources in the observation field of view and to output a catalogue of their locations and width parameters This step also produces images e SPECTRAL mode In this mode spiros reconstructs spectra of sources in the SPI field of view Source positions are either taken from the source location process IMAGING mode or from a catalogue The output spectra can be used
59. of the considered sources needs to be characterized Therefore the ARFs do not need ISDC SPI Analysis User Manual Issue 0 9d1 26 Nc N_CHAN 1 N CHAN 2 D gt LO THRES L foe de eode on NS A eee A F_CHAN 1 FCHAND Ec Figure 13 Illustration of the RMF compression scheme with a N_GRP 2 case to cover the full z y plane However as the source relative position depends on the location of the pointings a set of ARF is required for each of them In this case the ARF coefficients are stored following the scheme used for the detector spectra For each pointing and for each detector three vectors contains the different ARF ARF1 ARF2 ARF3 coefficients for the different photon energy A set of three vector columns correspond to one source In the case of XSPEC multi sources spectral fitting one set of three columns should be generated for each of the considered sources Unlike the ARFs stored as IRF the above ARFs are fully specific They should be derived for each observation and they cannot be re used As the RMFs are assumed to be independent of detector and direction a generic set can be used Their format is as shown above however the number of rows of the RMF should match the number of element of the ARF vectors They both represent the number of photon energy bins considered ISDC SPI Analysis User Manual Issue 0 9d1 27 8 Scientific Analysis There is a simple way to run Scientific Analys
60. ons with 156 unknowns would need to be solved This is impossible and the only way to increase the number of equations and make the system solvable is to observe more pointings Thus in order to solve this problem of background determination an appropriate dithering strategy has to be adopted for every observation Dithering is also important to improve the image quality of reconstructed sky images The dithering strategy that has to be adopted depends on the circumstances e observations of a single point source of known location where there are no known other objects of significant intensity in the field of view fully and partially coded for all dithering points i e within a radius of about 20 In this case the hexagonal dithering pattern can be used where a hexagonal scan is performed with one pointing centered on the source surrounded by six pointings with distances of 2 Note that the number of sources for which this dithering pattern can be used is very limited e observations of a region of multiple or complex sources or of sources with poorly known position In this case the 5 by 5 rectangular dithering pattern should be used where 25 points on a rectangular grid with 2 spacing around the source position are observed Both dithering patterns use a dwell time of 30 minutes per point This is optimized for the instrument performance and expected background variations All SPI observations should use dithering since reconstructio
61. or 19 background scaling coefficients one per detector in the image reconstruction process spiback can output several background components that can later be used independently in the imaging solution which then solve for several sets of 19 coefficients For example one can combine one model following the IREM time variations with another following the ACS count rate variations The model background rates computed are averages over the corresponding period of good times These rates are then multiplied by the livetime s to produce the final background counts stored in the output data structure The resulting background rates detector spectra are formatted as the events detector spectra Input Output in og dol string DOL of the input fits file which identifies the observation group to be processed out og dol string DOL of the output observation group e g og spi fits GROUPING ISDC SPI Analysis User Manual Issue 0 9d1 36 back mod idx string Name of output background index data file e g spi backgr index fits SPI BMOD DSP IDX tpl back mod dol string Name of the output background model data file This file will be in the same directory as the index data file e g backgr model fits gti dol string DOL of the input FITS file containing the list of good time in tervals for each detector and pointing deadtime dol string DOL of the input FITS file containing the list of deadtime cor rection fact
62. ors and livetimes for each detector and pointing ebounds dol string DOL of the FITS table containing the energy bin boundaries or raw pulse height as produced by spihist pointing dol string DOL of the FITS table containing the observation pointing di rections evts det spec dol string DOL of the FITS table containing the detector event spectra constant background model back const string if you want a constant background component you should enter YES otherwise NO e g YES back const value if you want to have a constant background component you should specify the background level cnts det sec kev e g 1 e 5 linear background model back linear if you want a linear background component you should enter YES otherwise NO e g NO back linear mjd0 this parameter specifies the start time of the linear background component as Modified Julian Date back linear slope this parameter specifies the slope of the linear background com ponent cnts sec det kev day sinusoidal background model back sincos string if you want a sinusoidal background component you should enter YES otherwise NO e g NO back sincos mjd0 real this parameter specifies the phase of the SIN COS background component as Modified Julian Date back sincos period real this parameter specifies the period of the SIN COS component days ISDC SPI Analysis User Manual Issue 0 9d1 37 ba
63. p index file e g spi skymax index fits SPI SK Y IMA IDX tpl image int string Name of the output skymap images file e g skymax image fits source res dol string DOL of the output source catalogue with flux spectra and error bars e g spi spiskymax sources fits SPI SRCL RES tpl energy range min integer minimum energy range sequence number as in ebounds file 1 2 3 energy ranges energy range min to energy range max are processed e g 1 energy range max integer maximum energy range sequence number e g 1 skymap system string Input skymap coordinate system C celestial G Galactic e g C image fov string Choice of how the image field of view is defined Must be one of SURVEY USER POINTING POINTING FCFOV POINTING ZCFOV POINTING CENTER The choice of POINTING FCFOV will set the centrepoint of the im age array to that of the observation field of view The size of the image field of view is extended by the FULLY CODED field of view of SPI about 8 e g POINTING FCFOV max_iter integer maximum number of iterations e g 50 image_default real image default intensity cm sr s The value to be as signed to pixels which are unconstrained by the data Set to the expected average intensity This parameter can be adjusted to optimize the maps but the result should not be too sensitive to its value e g 1 e 3 Source
64. pectra of all events including vetoed events are accumulated and transmitted every 30 minutes In case the SPI telemetry is continuously overflowing due to background radiation that is higher than expected or due to a strong solar flare the instrument can be operated in a degraded science mode TM emergency mode In this case the on board processing and transmission of data will be restricted to good events non vetoed ACS off energy spectra and PSD events The maximum data generation rate in this mode will be about half the rate for normal photon by photon mode The observer cannot select the TM emergency mode it is commanded by the ground controllers in case of need Before any change of mode the SPI instrument will be put into a special configuration mode This is the only mode in which changes to the instruments configuration can be made The instrument will not be taking scientific data when in configuration mode science telemetry processing is stopped Several other special modes are available for early in the mission for engineering tasks e g annealing and for instrument calibrations e g PSD calibration ISDC SPI Analysis User Manual Issue 0 9d1 7 3 3 Dead Time Due to several causes e g veto signals the SPI instrument experiences within a normal exposure a dead time during which no useful scientific data are collected Simulations and tests have shown that this dead time is about 12 of the observing time However
65. piros image index fits This file contains an index for all image data structures SPI SK Y IMA generated by spiros In this file you can find the information about the energy range for each image the exposure time and the number of iterations used by spiros Spiros image index intensity 1 fits Spiros image index intensity 2 fits spiros image index intensity m i fits These files contain the intensity map of the desired sky refion after the iterative removing of 0 1 m sources Spiros image index error 1 fits Spiros image index error 2 fits spiros image index error m i fits contain corresponding error maps The iterative significance maps are written to Spiros image index sigma 1 fits Spiros image index sigma 2 fits spiros image index sigma m 1 fits and the resulted significance map Spiros image index sigma result fits The spiros catalogue of found known sources can be found in ISDC SPI Analysis User Manual Issue 0 9d1 44 source_res fits This file contains data structure SPI SRCL RES with the following columns Column name Description SOURCE_ID DAY ID NAME CLASS RA_OBJ DEC_OBJ ERR RAD RELDIST SPA MODL SPA NPAR SPA PARS SPE MODL SPE NPAR SPE PARS VAR_MODL VAR_NPAR VAR_PARS COMMENTS SPLFLUX_1 SPLFLUX 2 ISGR FLUX 1 ISGR FLUX 2 PICS FLUX 1 PICS FLUX 2 JEMX FLUX 1 JEMX FLUX 2 E_MIN E MAX FLUX FLUX_ERR SEL_FLAG ISDC unique source ident
66. ry 30 minutes 2 5 The Plastic Scintillator Anti Coincidence Subassembly PSAC The purpose of the plastic scintillator subassembly PSAC is to reduce the 511 keV background due to particle emission by the passive mask The detector consists of a plastic scintillator inside a light tight box located just below the passive mask It has a good gamma ray transparency and actively detects particles which deposit energies in excess of 300 keV The light flashes that are produced by the impacts of these high energy particles are detected with four photo multiplier tubes located around the light tight box and converted into electrical pulses which are processed by the PSAC electronics assembly The electronics send a veto signal associated with the detected events and compatible with the Anti Coincidence Subassembly ACS Front End electronics veto signal to the veto control unit of the ACS 2 6 Electronics The electronics is divided into the Digital Front End Electronics DFEE and the Data Processing Electronics DPE The DFEE is in charge of the real time acquisition assembly time stamping and intermediate storage of the various pieces of information coming from the SPI front end systems detector electronics PSD ACS etc The DFEE will subdivide the events into classes depending on their origin in the instrument detector electronics Ge detectors PSD veto shield and will handle overall event energies and system monitoring statistics dead ti
67. source positions and fluxes spiskymax spiros ISDC SPI Analysis User Manual Issue 0 9d1 22 7 Low Level Processing Data Products 7 1 Event Types The photon which entered the telescope can be detected due to its interaction with the absorbing material of the detector Three major types of interactions play a dominant role photoelectric absorption Compton scattering and pair production In the photoelectric absorption process a photon undergoes an interaction with an absorber atom in which the photon completely disappears In its place an energetic photoelectron is ejected by the atom The photoelectron carries off most of the original photon energy The Compton scattering takes place between the incident gamma ray photon and an electron in the absorbing material The incoming photon is deflected and it transfers a portion of its energy to the electron The energy transferred to the electron can vary from zero to a large fraction of the initial gamma ray energy In the pair production process the gamma ray photon disappears and is replaced by an electron positron pair The positron will annihilate in the absorbing medium and two annihilation photons are normally produced as secondary products of the interactions Depending on the size of the detector and on the energy of the incoming photon a photon scattered in a Compton interaction can escape the detector or undergo a second interaction The pairs of 511 keV photons produced by the annihilat
68. st bins event data for individual detectors and or for the entire detector array using the binning defined by spibounds The events are grouped by pointing direction Binned data can be produced in counts counts s bin or counts s keV The available output FITS file formats are ISDC data structure or OGIP PHA II formats spihist creates event arrays in the form of detector count spectra according to various selection criteria and parameters ISDC SPI Analysis User Manual Issue 0 9d1 34 Input Output in og dol DOL of the input fits file which identifies the observation group to be processed det spec dol Output FITS structure containing binned detector spectra and uncertainties e g spi evts_det_spec fits SPI OBS DSP tpl out og dol DOL of the output observation group e g og spi fits GROUPING You can specify the output file outfile The name of the output file with SPI events binning in case you want to run a script for specific scientific windows swg index dol DOL of the input FITS file containing the index of science win dows to be analyzed gti dol DOL of the input FITS file containing the list of good time in tervals for each detector and pointing deadtime dol DOL of the input FITS file containing the list of deadtime cor rection factors and livetimes for each detector and pointing ebounds dol DOL of the FITS table containing the energy bin boundaries or raw pulse height as produced by spihist
69. t or source isdc scripts login ISDC ENV isdc integration spi int sw rep ROOTSYS isdc soft platform root Before starting the analysis in your home directory you should create a directory pfiles with the parameter files To do this give the following commands they are different in case you don t work at the ISDC cd mkdir pfiles cp home isdc_guest spi_int pfiles par pfiles if you work at ISDC or cp ISDC ENV pfiles par pfiles in any other environment Now you should create the directory data rep and the directory obs cd mkdir data rep cd data rep mkdir obs To set the links to the reference orbit test data at ISDC give the following commands ln s isdc testdata e2e e data cons ops 1 scw scw ln s isdc testdata e2e e data cons ops 1 ic ic ln s isdc testdata e2e e data cons ops 1 idx idx ln s isdc testdata e2e e data cons ops 1 aux aux To use other local data sets do similar linking e g ln s here are the prepared data scw scw ISDC SPI Analysis User Manual Issue 0 9d1 50 and similar for ic idx aux In the scw directory you can easily see which revolution numbers are available ls scw Now you have to create an observation group To do this you should specify science windows you want to analyze Open with an editor an ASCII file dols txt e g emacs dols txt and type in the following scw 0087 008700010010 000 swg_prp fits 1 scw 0087 008700020010 000 swg_prp fits 1 s
70. t To remove this background a proper mapping of the source and the surroundings is necessary This is the main reason why hexagonal dithering should only be used for isolated point sources where no significant contribution is expected from other sources with about 20 In order to allow the observer to estimate the significance of an off axis detection we give the ISDC SPI Analysis User Manual Issue 0 9d1 15 ph em2 a keV leg Flux 1 2 3 4 log Energy keV Figure 6 The continuum sensitivity of the SPI instrument for a 3 sigma detection in 10 seconds on axis The fluxes are for E AE 2 The dashed lines indicate extrapolations from the X rays using an powerlaw with photon index 2 for 1 10 and 100 mCrab 45 ph cmz 2 log Tluz 1 2 3 4 log Energy keV Figure 7 The narrow line sensitivity of the SPI instrument for a 3 sigma detection in 10 seconds Note that the 511 keV line is not shown in this figure ISDC SPI Analysis User Manual Issue 0 9d1 16 Energy Resolution Continuum a Line sensitivity E keV ph cm s keV ph cm7 s7 Table 4 The energy resolution FWHM narrow line and continuum sensitivities of the SPI instrument 3c detection in 10 seconds ISDC SPI Analysis User Manual Issue 0 9d1 17 Degradation factor E MeV Figure 8 The degradation factor of the line sensitivity for broad lines with a width of 1 3 and 10 of the line energy as a functio
71. tion with the source location precision srclocprec or width precision srcwidprec to stop improving source location or width values e g 0 2 srclocprec real In searching for sources SPIROS is always allowing them to si multaneously float to more accurate locations and this pa rameter is the location precision stopping criteria In iteratively finding better locations SPIROS finds the largest change the location of any source If it falls within the value of srclocprec and the change in the ML parameter within maxlikprec then the current source locations are returned as optimal e g 0 01 ISDC SPI Analysis User Manual Issue 0 9d1 43 srcwidprec In searching for POINTLIKE sources SPIROS also allows their widths to vary If the largest change in any source width falls within srcwidprec and the change in the ML parameter within maxlikprec then the current source widths are returned as op timal e g 0 1 solution constr Here the user can tell SPIROS to solve its imaging equations lin early NONE or with a positivity constraint POSITIVE e g NONE chilocstep Source location sampling step degrees e g 0 1 chiwidstep Source width sampling step degrees e g 0 5 The results produced by spiros are written into the directory spi After running program in IMAGING mode with nofsorces m you will find the following files if you don t modify the names in the parameter file S
72. to the common on board time OBT and derives the true multiplicity of the event This information is written to the set of prepared PRP data files for each Science Window All the previous steps are done at ISDC and can t be redone by user That s why we describe it only briefly and in the following sections we concentrate on the Scientific Analysis The different tasks of Scientific Analysis are summarized in Figure 9 The three or four big letters indicated in the boxes give the task acronyms It starts with an observation group of prepared data The subsequent resulting data are shown on the right and after each step the newly created data are attached to the observation group Any data of the observation group can then be used as an input for later tasks The task Build Observation Group creates prepared ISDC Observation Groups OG according to such criteria as time intervals sky coordinates instrument modes list of Science Window Groups SWGs IDs etc or a combination of them The Observation Group points to an index of science windows related to a number of prepared Science Window Groups The tasks displayed in Fig 9 are described in some details below COR Data Correction 1 Computes the event energy in keV from the channel energy PHA using a calibration index file and 2 derives a ground derived PSD localized unlocalized flag from the PSD prepared data This task is fulfilled by he executable spi_gain_corr PO
73. tor column with the length equal to the number of energy bins defined in spibounds Upper energy boundaries vector column with the length equal to the number of energy bins defined in spibounds Flux values vector column with the length equal to the number of energy bins defined in spibounds Flux errors vector column with the length equal to the number of energy bins defined in spibounds Source selection flag 0 in case of no problems 1 in case of the problems ISDC SPI Analysis User Manual Issue 0 9d1 45 The spectrum information is upgraded in this file after running spiros in SPECTRAL mode The additional files that appear after this run in the directory spi are source _spec _index fits with an index and output observation group source _spec _index _data fits with the spectrum of each source found For each source the data structure SPI SRC SPE is filled The meaning of the columns in the fits table is described in the next Table Column name Description CHANNEL Channel numbers for the countrates RATE Countrates in the defined channels STAT_ERR Statistical uncertainty of the countrates SYS_ERR Systematical uncertainty of the countrates QUALITY Quality flags for the channels GROUPING Grouping flags for the channels After running spiros in TIMING mode the following files will be added to the spi directory source _timing _index fits source _timing _index _data fits The first on
74. ty of the X axis in arc minutes e g 1 0 Tolerance on the stability of the Z axis in arc minutes e g 1 0 Additional parameters Defaults to yes Lets you overwrite the pointing structure The spipoint output file in the directory spi e g spi pointings fits in the given example contains in a data structure SPI OBS PNT an information about ISOC and SPI pointing ID columns PTID ISOC and PTID SPI the OBT and ISDC JD start and end time of the period columns OBT START OBT_END TSTART and TSTOP the duration of pointing in seconds column TELAPSE and the attitudes of the SPI X and Z axes columns RA SPIX DEC_SPIX RA SPIZ and DEC SPIZ The schematic representation of this data structure can be found in Figure 15 8 5 SPI Good Time Handling spi_gti_creation spi_gti_creation selects criteria for defining the good time and derive the Good Time Interval GTI to be used for event selection in the current analysis Also the detectors and event types which will be used for the analysis are defined here Type Description rwgroup string DOL of the read write group for input and output e g og_spi fits GROUPING rwgti string output GTI data structure e g spi gti fits SPL OBS GTI tpl ISDC SPI Analysis User Manual Issue 0 9d1 31 string List of detectors and pseudo detectors used for the analysis 1 will give all single PSD events detector 0 to 18 Detector IDs up to 141 are allowed
75. uilding a new library Then the new library will be uploaded All events detected by SPI are classified in accordance with how many detectors respond to an incoming photon The event detected by only one detector is called either PSD event or single event according to whether it was processed by PSD or not Multiple events are detected by several detectors and the value of multiplicity corresponds to the number of the detectors hit Events that were detected only by PSD are called pure PSD events 7 2 Raw Data All scientific event and PSD curve data formatted as blocks are transmitted in 4 telemetry packets of identical structure corresponding to the operational emergency calibration and diagnostic modes The packets corresponding to the modes that do not occur are empty Two raw data files are created for each pointing spi raw_block fits for the house keeping data and spi_raw_oper fits for the event data In the following we descibe the analysis of the operational mode only as it is the only mode important for the Science Data Analysis The file spi raw_oper fits includes 14 substructures Each data substructure corresponds to one type of event The names of the data structures and the corresponding event types are presented ISDC SPI Analysis User Manual Issue 0 9d1 23 Event Type SINGLE PSD PURE PSD LTIPLE PSD LTIPLE PSD MULTIPLE PSD MULTIPLE PSD MULTIPLE PSD Table 6 spi_raw_oper fits Raw Data Structure
76. wee A depo e eed amp mAessccs 6 3 Instrument Operations 7 3 1 How the instrument works less T 3 2 Operating Modes s 2 442449 y 4 Ve AS ERR UE EEESS4a4 E T 2 9 Dead Time lulu dee ES X UR LEA UA adde UR eee eA SS 8 3 4 Telemetry Budget sasaaa i aaa a ee eee ENTE ADADER ES ES 8 4 Using the Instrument 9 4 1 Spectroscopy amp Timing 9 4 2 Imaging 0064 244 Ad Eos Eoo on en Ro AST E Py d UP s ode 9 4 3 Gamma ray Burst Detection eA 10 5 Performance of the Instrument 11 5 1 Components and Sources of Instrumental Background 0 11 5 1 1 Continuum Background ee 11 5 1 2 511 keV Background ee ee 11 5 1 3 Background Gamma Ray Lines ees 12 ISDC SPI Analysis User Manual Issue 0 9d1 iii 5 2 Instrumental Characterization and Calibration 5 3 Measured Performance 22222 sh 5301 Imaging Resolution x 40m He PARR ad 5 3 2 Spectral Resolution 2222s 5 3 3 Sensitivity a Lov spp X n h po 4 BA a WORD e CPGE do oh A ee UR 5 3 4 Dithering Sensitivity Degradation 5 8 5 Detection of of axis sources es 5 3 6 Imaging Capabilities 2e 53 1 Timing Capabilities eu 20 9084 44 Ros emo m Oe RR Ae ede II Data Analysis 6 Overview 7 Low Level Processing Data Products 7 1 7 2 7 3 7 4 Event Types o 4 ki bus AE Rem Peur a eh A ole i Raw Datan oa ux rara ese Sod od At hh omi US
77. y the detector and the other escapes a 511 keV background event is produced e shield leakage 511 keV photons originating from interactions of cosmic rays with passive spacecraft materials that are not rejected by the BGO shield e mask component 511 keV photons originating from cosmic ray interactions with the mask material The main source is pair creation by cosmic ray proton interactions with W nuclei This component can be reduced significantly with the Plastic Scintillator e BGO shield blocking time component 511 keV photons produced by 8 decays in the BGO shield when the ACS electronics is blocked by a large energy deposit and the veto is on ISDC SPI Analysis User Manual Issue 0 9d1 11 10 erture flux elastic neutron shield leakage B localized 1 p non localized 10 B mask emission Total 9 107 gt E eo 10 ce a 3 10 10 i z 10 10 10 E Mev Figure 3 The continuum background components for SPI The individual components are identified The total background spectrum is indicated with the black line All these components were calculated with a Monte Carlo method The resulting line strengths for the 511 keV line with and without the PSAC are given in Table 2 1 2 x 107 2 1 x 107 BGO shield 14x107 1 4x 107 blocking time Total 3 2 x 107 5 2 x 107 Table 2 511 keV background line strength with and without PSAC Calculations are for 5 cm
78. ymax_energy_rangemin 1 spiskymax_energy range_max The results produced by the script can be found in the directory spi The main interest represent files spiros_image_index_sigma_result fits with the significance map build by spiros and sky max_image fits with the intensity map build by spiskymaz The easiest way to look to this images is to type fv and the name of the file e g fv skymax_image fits Then the following table appears Summary of skymax_image fits in homes Press button Image and you will see the resulted intensity map you can modify the color scheme using colors menu ISDC SPI Analysis User Manual Issue 0 9d1 53 skymax_image fits_2 DEC CAR deg A 60 80 100 120 140 160 RA CAR deg ISDC SPI Analysis User Manual Issue 0 9d1 54 10 Known Limitations TBW ISDC SPI Analysis User Manual Issue 0 9d1 55 References 1 ISDC INTROIDA Introduction to the INTEGRAL Data Analysis ISDC SPI Analysis User Manual Issue 0 9d1 56

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