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Data Products

Data Products. David Band and a cast of thousands. Data Products Used by SAE. Here we discuss the data products (DPs) that result from Level 1 processing (reconstruction for the LAT, calibration for the GBM) and will be used by Level 2 data analysis (e.g., fitting spectral models).

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Data Products

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  1. Data Products David Band and a cast of thousands

  2. Data Products Used by SAE • Here we discuss the data products (DPs) that result from Level 1 processing (reconstruction for the LAT, calibration for the GBM) and will be used by Level 2 data analysis (e.g., fitting spectral models). • These are the DPs that will be provided to the general scientific community, and will be the beginning for almost all astrophysical data analysis. • These DPs are FITS files. FITS files consist of a series of units, each with an ASCII ‘header’ and a binary data table. FITS files can be read by the tool ‘fv.’ • Only some of the DPs will be necessary in DC2.

  3. Science Data Products ICD • The files are defined by the Science Data Products ICD : glast.gsfc.nasa.gov/ssc/dev/current_documents/Science_DP_ICD.doc • The development status of all the DPs is summarized at glast.gsfc.nasa.gov/ssc/dev/data_products/science_data_products.html which includes links to sample files. • The file names provide the DP type, detector, version number, time or burst name, etc. For example: GLG_TTE_N4_BN070509400_V01.FIT • Note: an Operations Data Products ICD (timelines, Level 0 data) has been baselined and is maintained by the MOC. FITS file GLAST DP GBM Version number Time-Tagged Events Burst name NaI detector #4

  4. The LAT’s Photon DPs • Most of the LAT tools operate on photon files (called FT1)—lists of LAT photons—and their auxiliary pointing/time history files (called FT2). • FT1 and FT2 files are extracted from GSSC or LISOC databases for a specific analysis. Further selections can be made (tool=gtselect). • FT1 files are subsets of event files and contain information (arrival time, apparent energy, direction, etc.) required by the analysis tools for events identified as photons • The FT1 files include the criteria used to select the photons (e.g., region, energy). • Additional information for each event can be found in the event files (called FT0). • The pulsar tools add information to the FT1 files. • FT2 files provide GLAST’s position, orientation, and livetime every 30 seconds.

  5. Other LAT Files • The Instrument Response Functions (IRFs) will be in files stored in a CALDB file system. The SAE knows how to access these files, and therefore the average investigator need not. • Catalog files • Pulsar ephemerides

  6. GBM DPs—Daily Data • The GBM will produce burst and non-burst DPs. • The daily versions of the continuous DPs provide the binned count rates from the 12 NaI and 2 BGO detectors, whether or not a burst has been detected. • CTIME: 8 energy channels every 0.256 s • CSPEC: 128 energy channels every 8.192 s • For DC2 we are providing CTIME and CSPEC for the detectors facing the burst, with at most one burst per file. • There are no tools that use these data. • There are also housekeeping, calibration and catalog files that during the mission will be produced on various timescales, but are not being provided for DC2.

  7. GBM DPs—Burst Data • The GIOC will provide a number of burst-related DPs. • Time-tagged events (TTE)—a list of counts from the burst • During the mission TTE data from all detectors, one file per detector, will be provided • All detectors because the spacecraft may slew during a burst • For DC2 we are providing TTE files only for the burst-facing detectors • The counts are in one of 128 energy bins • CTIME and CSPEC—burst versions of the daily DPs • Rates from 4000 s before to 4000 s after the trigger • Again, during the mission all detectors will be included • For DC2 only the burst-facing detectors will be provided • Again, these data are not used by any tool

  8. GBM DPs—Auxiliary Burst Files • Detector Response Matrices (DRMs)—the mapping between the input spectrum and the binned count spectrum. • During the mission the GIOC will provide an RSPII file for each detector with multiple DRMs per file • For DC2 simple RSP files with one DRM per file • During the mission the SAE will include a tool for users to calculate their own DRM file • Background—the background rate for each detector in 128 energy bins • During the mission the background file will also include a polynomial model of the background • For DC2 a constant background is assumed • During the mission users will be able to calculate their own background file

  9. Binned GBM Spectral Analysis • Note that for DC2 you will be provided with: • Unbinned (in time) burst counts • DRMs • Background spectra • Using the binning tool (gtbin) you can produce binned burst spectra (i.e., PHA files) • You now have all the ingredients for XSPEC-style spectral analysis.

  10. GBM DPs—TRIGDAT • When the GBM or the LAT detects a burst, it will telemeter data to the ground through TDRSS. • These TRIGDAT messages provide: • Burst localization • Lightcurves • Background rates • Whether an autonomous repoint was recommended • The GIOC will package the GBM’s TRIGDAT messages into a FITS file and provide it with the other burst data • Some simulated GBM TRIGDAT messages will be provided in DC2.

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