The GLAST Data

1
The GLAST Data

• David Band
• (GLAST SSCGSFC/UMBC)

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

3
What Is GLAST?

• Gamma-ray Large Area Space Telescope (GLAST)
  successor to CGRO
• Large Area Telescope (LAT)GLASTs main
  instrument, a follow-on to CGROs EGRET. The LAT
  is a NASA-DOE collaboration with foreign
  contributions. PI Peter Michelson (Stanford
  SLAC)
• GLAST Burst Monitor (GBM)a smaller version of
  CGROs 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.

4
The LATCharacteristics

• The LAT will be a pair conversion telescope.
• Elt20 MeV to gt300 GeV, ?E/E lt10 on axis for
  0.1-10 GeV.
• Peak effective areagt8000 cm2.
• FOVgt2 sr, with Aeff1/2 of normal at 55
• 1? angular resolution lt3.5 _at_100 MeV, lt0.15 _at_10
  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 gt30? more sensitive than EGRET!
  The EGRET 3rd Catalog had 271 sources, LAT
  catalog should have gt9000. Localizations will
  allow ???? observations.

5
The GBM

• 12 NaI(Tl) detectors (5? diameter)lt10 keV to 1
  MeV
• 2 BGO detectors (5? long, 5? diameter)to gt25 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.

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The Science of GLAST

• Blazars AGNrelativistic jets, transients
• Gamma-ray burstsrelativistic outflows, efficient
  emission of gamma rays, new emission component?
• Pulsarsdistinguish between outer gap and polar
  cap models, young sources
• Unidentified sourcesfaint blazars? New Galactic
  population?
• Diffuse Galactic emissioncosmic rays interacting
  with Galactic gas. Both an annoying background
  and an intrinsically interesting phenomenon
• Extragalactic IRattenuates extragalactic gamma
  rays
• Solar flaresparticle acceleration
• Exotic particlesdecay or annihilation

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Data Analysis Issues

• The PSF is large at low energy, small at high
  energy.
• With the LATs large effective area, many sources
  will be detected their PSFs will merge at low
  energy.
• Analysis is inherently 3D2 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.

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).

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Special Cases

• Bursts are (relatively) short, and the pointing
  will not change significantly during the burst
• Within the bursts PSF no non-burst photons are
  expected during the burst.
• Thus bursts can be analyzed as an isolated
  source
• Many burst photonsbin in time and energy, fit
  spectra (e.g., with XSPEC)
• Few burst photonsfit 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.

10
The Ground System
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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.

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.

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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 teams
  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

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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 LATs 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.

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Databases

• The SSC will maintain all its databases in a form
  compatible with HEASARC norms. The SSCs
  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 SSCs computer system will be
  provided by the HEASARC while the data disks will
  be purchased by the SSC. The SSCs computers
  will be part of the HEASARCs system, and will
  participate in the HEASARCs 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.

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Programmatics

• Mike Corcoran is the SSCs 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.

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Summary

• GLASTs 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.

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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 HEASARCs liason with SSC.
• PDMP drafted, SSC-FRD baselined, HEASARC-SSC MOU
  drafted, data products defined.

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Additional Slides
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(No Transcript)
21
The LATStructure

• The LATs 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 trackers front
  or back may be analyzed separately.

Anticoincidence Detector
Tracker
Calorimeter
22
LAT Science Performance Summary
Presentat PDR, will be revised
23
Large FOV

• FOVgt2 sr
• Aeff1/2 of normal at 55
• Photons at large angles to normal will be
  scientifically usable.
• Plot is from the proposal

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Many More Sources Expected
EGRET 3rd Catalog had 271 sources gt9000 sources
expected in 1st LAT catalog!
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More AGN!

• Many more AGN will be detected!

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Better Source Localization

• 172 of the 271 sources in the EGRET 3rd catalog
  are unidentified
• Better locations will permit multiwavelength
  followups

27
Comparison Between GLAST and Other Gamma-Ray
Missions
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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

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COMPONENTS OF THE ENVIRONMENT (2)
Pulsar ephem. (D4)
Pulsar period search (A4)
Ephemeris extract (U11)
Event display (UI1)
Level 0.5
Pulsar profiles (A3)1
LAT Point source catalog (D5)
Pulsar phase assign (U12)
Arrival time correction (U10)
Data extract (U1)
Level 1 (D1)
Source model def. tool (U7)
Src. ID (A2)
Catalog Access (U9)
Exposure calc. (U4)
Pt.ing/livetime extractor (U3)
Pointing/livetime history (D2)
Likelihood (A1)
Astron. catalogs (D6)
Alternative source for testing high-level analysis
Alternative for making additional cuts on
already-retrieved event data
Interstellar em. model (U5)
Map gen(U6)
IRFs (D3)
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.
Observation simulator (O2)
Data sub- selection (U2)
GRB unbinned spectral analysis (A9)
IRF visual- ization (U8)
Pt.ing/livetime simulator (O1)
Pt.ing/livetime extractor (U3)
GRB spectral-temporal modeling (A10)
GRB LAT DRM gen. (U14)
GRB spectral analysis (A8)2
GRB visual- ization (U13)
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.
GRB rebinning (A6)2
GRB temporal analysis (A7)2
GRB event binning (A5)
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Databases
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Utilities
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Utilities, Cont.
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Analysis Tools
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Observation Simulators
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User Interface