GLAST Science Support CenterFebruary 14, 2003 HUG Meeting The GLAST Data David Band (GLAST SSC—GSFC/UMBC)

GLAST Science Support Center February 14, 2003 HUG Meeting—2 Outline Description of the GLAST Mission Novel Aspects of GLAST Data Analysis The Ground System –The SSC –Community Access to the Data –Analysis Software –Databases –Programmatics Summary

GLAST Science Support Center February 14, 2003 HUG Meeting—3 What Is GLAST? Gamma-ray Large Area Space Telescope (GLAST)— successor to CGRO Large Area Telescope (LAT)—GLAST’s main instrument, a follow-on to CGRO’s EGRET. The LAT is a NASA-DOE collaboration with foreign contributions. PI: Peter Michelson (Stanford & SLAC) GLAST Burst Monitor (GBM)—a smaller version of CGRO’s BATSE. The GBM is a MSFC-German collaboration. PI: Chip Meegan (NSSTC) Scheduled launch is September, 2006, into low earth orbit The minimum mission is 5 years, with a goal of 10+ years! Additional details in the extra slides at the end.

GLAST Science Support Center February 14, 2003 HUG Meeting—4 The LAT—Characteristics The LAT will be a pair conversion telescope. E= 300 GeV,  E/E <10% on axis for GeV. Peak effective area>8000 cm 2. FOV>2 sr, with A eff ~1/2 of normal at 55° 1  angular resolution MeV, GeV Only a few Hz out of the 30 Hz events telemetered to Earth will be photons. The basic data are event lists. In normal operation GLAST will survey the sky, thus most sources will be observed at a variety of angles to the LAT. The LAT will be >30  more sensitive than EGRET! The EGRET 3rd Catalog had 271 sources, LAT catalog should have >9000. Localizations will allow  observations.

GLAST Science Support Center February 14, 2003 HUG Meeting—5 The GBM 12 NaI(Tl) detectors (5  diameter)—<10 keV to ~1 MeV 2 BGO detectors (5  long, 5  diameter)—to >25 MeV The combination of the GBM and LAT will provide spectral coverage from ~10 keV to ~300 GeV--7.5 decades! Bursts will be localized both onboard and on the ground. GCN should receive the first notification in ~7s. The GBM will provide: binned background data; and binned and event data after a trigger.

GLAST Science Support Center February 14, 2003 HUG Meeting—6 The Science of GLAST Blazars & AGN—relativistic jets, transients Gamma-ray bursts—relativistic outflows, efficient emission of gamma rays, new emission component? Pulsars—distinguish between outer gap and polar cap models, young sources Unidentified sources—faint blazars? New Galactic population? Diffuse Galactic emission—cosmic rays interacting with Galactic gas. Both an annoying background and an intrinsically interesting phenomenon Extragalactic IR—attenuates extragalactic gamma rays Solar flares—particle acceleration Exotic particles—decay or annihilation

GLAST Science Support Center February 14, 2003 HUG Meeting—7 Data Analysis Issues The PSF is large at low energy, small at high energy. With the LAT’s large effective area, many sources will be detected; their PSFs will merge at low energy.  Analysis is inherently 3D—2 spatial and 1 spectral (& users are interested in temporal!) Complicated, multi-parameter source models will include: –All sources within a few times the PSF of the region of interest –Diffuse sources (e.g., supernova remnants) –Diffuse Galactic and extragalactic emission (modeled) The LAT will usually survey the sky. Therefore a source will be observed at different instrument orientations. The instrument response function will be a function of many quantities.

GLAST Science Support Center February 14, 2003 HUG Meeting—8 Planned Basic Analysis Strategy We plan to detect sources, determine source intensities, fit spectral parameters, set upper limits, etc., using the likelihood  of the observed counts given a source model. Calculating the  will be difficult because many counts will sparsely populate an enormous data space (both the observed counts and the absence of counts must be considered). The  will be calculated many times. Therefore we want to isolate the factors that are not model-dependent, and calculate them once for a given analysis. Many of these quantities will have units of “exposure” (area  time).

GLAST Science Support Center February 14, 2003 HUG Meeting—9 Special Cases Bursts are (relatively) short, and the pointing will not change significantly during the burst Within the burst’s PSF no non-burst photons are expected during the burst. Thus bursts can be analyzed as an isolated source: –Many burst photons—bin in time and energy, fit spectra (e.g., with XSPEC) –Few burst photons—fit spectra using likelihoods; energy is the only observable The detection of pulsars will rely on their periodicity. Because of the low count rate, long time ranges will be searched, requiring both P and P-dot. Analysis of pulsar spectrum and intensity will require standard point source analysis.

GLAST Science Support Center February 14, 2003 HUG Meeting—10 The Ground System

GLAST Science Support Center February 14, 2003 HUG Meeting—11 The Role of the SSC The SSC is the interface between GLAST and the general scientific community. It is responsible for: –Providing data and analysis tools to the scientific community –Running the guest investigator program –Supporting mission operations, primarily through maintaining the mission timeline –Archiving the mission data, eventually in the HEASARC –Supporting the dissemination of results through the SSC website, running conferences and contributing to public education The SSC consists of scientists, scientific programmers and support staff housed within LHEA at GSFC. The SSC is NOT responsible for the basic data processing, and will not support a guest observer facility.

GLAST Science Support Center February 14, 2003 HUG Meeting—12 Community Access to the Data During the first year GLAST will survey the sky. The LAT team will verify their data and produce a point source catalog from the survey. A limited number of GIs will access the data through the instrument teams. In subsequent years all the data are public immediately. At all times data from transients are public immediately. GLAST will have a large, well-funded GI program. GIs may request pointed observations. The SSC will post results on its website (e.g., exposure maps). The PDMP has been drafted but not baselined. The PDMP will have the official statements of the data and transients policies.

GLAST Science Support Center February 14, 2003 HUG Meeting—13 The Standard Analysis Environment Standard analysis environment (SAE): tools and databases needed for routine analysis of GLAST data by both the instrument teams and the scientific community. SAE defined jointly by the LAT team and the SSC, and will be developed under the LAT team’s management with SSC participation. Mock data challenges in late ‘04 and late ‘05. The tools will support: –Likelihood analysis for source detection and spectral analysis –Gamma-ray burst spectral and temporal analysis –Pulsar periodicity analysis –Simulations –Catalog comparisons

GLAST Science Support Center February 14, 2003 HUG Meeting—14 Software Paradigm Our tools will be FTOOLs and use the HEADAS libraries: –Data I/O through FITS files, using existing types where possible –The PIL interface will extended to support GUIs The LAT’s software development environment will be used: –CVS for storing the software –CMT for configuration and build management –DOXYGEN for documenting the code –C++ for most new code –Support for Windows and Linux platforms Scripting language: Python (probably) Graphics (& GUI): Root (or plplot, with DS9) Existing tools will be used where possible (e.g., XSPEC for analysis of burst spectra). The systematic definition and design of the tools has begun. See the tables at the end.

GLAST Science Support Center February 14, 2003 HUG Meeting—15 Databases The SSC will maintain all its databases in a form compatible with HEASARC norms. The SSC’s databases will be owned jointly by the SSC and the HEASARC, and will remain as the mission archive after the SSC is disbanded. The list of photons must be searchable rapidly, and will probably be installed on a Beowulf system. The CPUs of the SSC’s computer system will be provided by the HEASARC while the data disks will be purchased by the SSC. The SSC’s computers will be part of the HEASARC’s system, and will participate in the HEASARC’s computer security plan. Data ingest from the other ground system components will be tested in Ground Readiness Tests (11/04, 9/05). Ground system end-to-end tests are planned. Ingest into the databases will also be tested in the analysis system mock data challenges.

GLAST Science Support Center February 14, 2003 HUG Meeting—16 Programmatics Mike Corcoran is the SSC’s contact at the HEASARC and the GLAST archive scientist. The HEASARC-SSC MOU is nearly complete; an ICD is planned. An ad hoc Data Products Working Group developed descriptions of the data products (down to FITS headers and table columns) that will be passed between ground system components. ICDs with the ground system components will be drafted by 11/03 and finished by 6/04. The SSC Functional Requirements Document has been baselined.

GLAST Science Support Center February 14, 2003 HUG Meeting—17 Summary GLAST’s primary instrument, the LAT, will be a large leap in capability and complexity relative to EGRET. The GBM is a smaller version of BATSE. The standard analysis of LAT data will be complex because: narrow PSF at high energy, broad at low energy; a region must be modeled to study a source; and GLAST will usually scan the sky. Most analysis will use the likelihood of the observed counts given a source model. Analysis of gamma-ray bursts and periodicity studies of pulsars will use the sources’ temporal properties. After the first year data will be public immediately. Transients are public even during the first year. There will be a large GI program. The instrument teams will process the telemetry into photon lists.

GLAST Science Support Center February 14, 2003 HUG Meeting—18 Summary, Cont. The SSC at GSFC will provide the scientific community with data and analysis tools through its website. The tools will be FTOOLs, extended to provide a GUI interface. Where possible we will use existing tools. New tools will be written in C++, and supported for Windows and Linux. The databases will be in a HEASARC-standard format. The photon list will be loaded onto a Beowulf cluster. After the mission the databases will remain at the HEASARC as the archives. Mike Corcoran is HEASARC’s liason with SSC. PDMP drafted, SSC-FRD baselined, HEASARC-SSC MOU drafted, data products defined.

GLAST Science Support Center February 14, 2003 HUG Meeting—19 Additional Slides

GLAST Science Support Center February 14, 2003 HUG Meeting—20

GLAST Science Support Center February 14, 2003 HUG Meeting—21 The LAT—Structure The LAT’s Tracker subsystem will consist of 16 tungsten planes (for pair production) and 18 silicon strips planes (to track the pairs). Below these W-Si planes are 8 planes of CsI “logs” to measure energies. Surrounding the LAT are plastic anti-coincidence scintillator tiles. Photons that pair- produce in the tracker’s front or back may be analyzed separately. Anticoincidence Detector Tracker Calorimeter

GLAST Science Support Center February 14, 2003 HUG Meeting—22 LAT Science Performance Summary 5 arcmin<10 arcminGRB localization <0.4 arcmin<0.5 arcminSource Location Determination 3x10 -9 cm -2 s -1 <6x10 -9 cm -2 s -1 Point Source Sensitivity(>100MeV) 6% diffuse (adjustable)<10% diffuseBackground rejection (E>100 MeV) 2.4 sr>2srField of View 1.6<1.7PSF 55º/normal ratio 2.1 front, 2.6 back<3PSF 95/68 ratio (100 MeV) 0.086° (front), 0.115° (total)<0.15°PSF 68% 10 GeV on-axis 3.37° (front), 4.64° (total)<3.5°PSF 68% 100 MeV on-axis <4.5%<6%Energy Resolution GeV off-axis <15%<20%Energy Resolution GeV on-axis 8%<10%Energy Resolution 10 GeV on-axis 9%<10%Energy Resolution 100 MeV on-axis 10,000 cm 2 at 10 GeV>8000 cm 2 Peak Effective Area (in range 1-10 GeV) Present Design ValueSRD ValueParameter Present=at PDR, will be revised

GLAST Science Support Center February 14, 2003 HUG Meeting—23 Large FOV FOV>2 sr A eff ~1/2 of normal at 55° Photons at large angles to normal will be scientifically usable. Plot is from the proposal

GLAST Science Support Center February 14, 2003 HUG Meeting—24 Many More Sources Expected EGRET 3rd Catalog had 271 sources >9000 sources expected in 1st LAT catalog!

GLAST Science Support Center February 14, 2003 HUG Meeting—25 More AGN! Many more AGN will be detected! Integral Flux (E>100 MeV) cm -2 s -1

GLAST Science Support Center February 14, 2003 HUG Meeting—26 Better Source Localization 172 of the 271 sources in the EGRET 3 rd catalog are “unidentified” Better locations will permit multiwavelength followups

GLAST Science Support Center February 14, 2003 HUG Meeting—27 Comparison Between GLAST and Other Gamma-Ray Missions

GLAST Science Support Center February 14, 2003 HUG Meeting—28 Spectral Coverage The combination of the GBM and LAT will provide spectral coverage from ~10 keV to ~300 GeV--7.5 decades! Model GLAST spectrum of GRB940217:

GLAST Science Support Center February 14, 2003 HUG Meeting—29 COMPONENTS OF THE ENVIRONMENT (§2) User Interface aspects of the standard analysis environment, such as Image/plot display (UI2), Command line interface & scripting (UI4), and GUI & Web access (UI5) are not shown explicitly. 1 This tool also performs periodicity tests and the results can be used to refine ephemerides 2 These tools can also take as input binned data from other instruments, e.g., GBM; the corresponding DRMs must also be available. Pulsar ephem. (D4) Level 1 (D1) LAT Point source catalog (D5) Interstellar em. model (U5) Pointing/livetime history (D2) Astron. catalogs (D6) Level 0.5 IRFs (D3) Alternative source for testing high- level analysis Alternative for making additional cuts on already- retrieved event data Pt.ing/livetime simulator (O1) Observation simulator (O2) Pt.ing/livetime extractor (U3) Data sub- selection (U2) Data extract (U1) Exposure calc. (U4) Likelihood (A1) Map gen (U6) Src. ID (A2) Event display (UI1) Pulsar profiles (A3) 1 Catalog Access (U9) Pt.ing/livetime extractor (U3) Pulsar phase assign (U12) Pulsar period search (A4) GRB spectral-temporal modeling (A10) Source model def. tool (U7) Arrival time correction (U10) GRB temporal analysis (A7) 2 GRB LAT DRM gen. (U14) GRB spectral analysis (A8) 2 GRB event binning (A5) GRB unbinned spectral analysis (A9) GRB visual- ization (U13) IRF visual- ization (U8) Ephemeris extract (U11) GRB rebinning (A6) 2

GLAST Science Support Center February 14, 2003 HUG Meeting—30 Databases

GLAST Science Support Center February 14, 2003 HUG Meeting—31 Utilities

GLAST Science Support Center February 14, 2003 HUG Meeting—32 Utilities, Cont.

GLAST Science Support Center February 14, 2003 HUG Meeting—33 Analysis Tools

GLAST Science Support Center February 14, 2003 HUG Meeting—34 Observation Simulators

GLAST Science Support Center February 14, 2003 HUG Meeting—35 User Interface