GLAST CDR

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GLAST Mission Status and Science
Opportunities Peter F. Michelson Stanford
University peterm_at_stanford.edu
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Outline

• GLAST An International Science Mission
• Large Area Telescope (LAT)
• GLAST Burst Monitor (GBM)
• Mission Operations Plan
• highlights of science opportunities
• schedule highlights

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The GLAST Observatory

• two GLAST instruments
• LAT 20 MeV gt300 GeV
• GBM 10 keV 25 MeV

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GLAST is an International Mission

• NASA - DoE Partnership on LAT
• LAT is being built by an international team
• (PI P. Michelson, Stanford University)
• Si Tracker UCSC, Italy, Japan, Stanford/SLAC
• CsI Calorimeter NRL, France, Sweden
• Anticoincidence GSFC
• Data Acquisition System Stanford/SLAC, NRL
• GBM is being built by US and Germany
• (PI C. Meegan, NASA/MSFC)
• Detectors MPE
• Data Acquisition System MSFC
• Spacecraft and integration - Spectrum Astro
• Mission Management NASA/GSFC
• ( K. Grady, Project Manager S. Ritz, Project
  Scientist)

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LAT experimental technique

• instrument must measure the direction, energy,
  and arrival time of high
• energy photons (from approximately 20 MeV to
  greater than 300 GeV)
• - photon interactions with matter in GLAST
• energy range dominated by pair
  conversion
• determine photon direction
• clear signature for background rejection

- limitations on angular resolution (PSF)
low E multiple scattering gt many
thin layers high E hit precision
lever arm
must detect ?-rays with high efficiency
and reject the much larger (1041) flux of
background cosmic-rays, etc. energy
resolution requires calorimeter of sufficient
depth to measure buildup of the EM shower.
Segmentation useful for resolution and
background rejection.
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Overview of LAT

• Precision Si-strip Tracker (TKR) 18 XY
  tracking planes. Single-sided silicon strip
  detectors (228 mm pitch) Measure the photon
  direction gamma ID.
• Hodoscopic CsI Calorimeter(CAL) Array of
  1536 CsI(Tl) crystals in 8 layers. Measure the
  photon energy image the shower.
• Segmented Anticoincidence Detector (ACD) 89
  plastic scintillator tiles. Reject background
  of charged cosmic rays segmentation removes
  self-veto effects at high energy.
• Electronics System Includes flexible, robust
  hardware trigger and software filters.

Systems work together to identify and measure the
flux of cosmic gamma rays with energy 20 MeV -
gt300 GeV.
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GLAST LAT High Energy Capabilities

• Huge FOV (20 of sky)
• Broadband (4 decades in energy, including
  unexplored region gt 10 GeV)
• Unprecedented PSF for gamma rays (factor gt 3
  better than EGRET for Egt1 GeV)
• Large effective area (factor gt 4 better than
  EGRET)
• Results in factor gt 30-100 improvement in
  sensitivity
• No expendables long mission without
  degradation

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High energy source sensitivity all-sky scan mode
100 sec
During the all-sky survey, GLAST will have
sufficient sensitivity after O(1) day to detect
(5s) the weakest EGRET sources.
EGRET Fluxes

• - GRB940217 (100sec)
• - PKS 1622-287 flare
• - 3C279 flare
• - Vela Pulsar
• - Crab Pulsar
• - 3EG 202040 (SNR g Cygni?)
• - 3EG 183559
• - 3C279 lowest 5s detection
• - 3EG 1911-2000 (AGN)
• - Mrk 421
• - Weakest 5s EGRET source

1 orbit
1 day
zenith-pointed
rocking all-sky scan alternating orbits point
above/below the orbit plane
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GBM Detector
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Roles of the GBM

• provides spectra for bursts from 10 keV to 25
  MeV, connecting frontier LAT high-energy
  measurements with more familiar energy domain
• provides wide sky coverage (8 sr) -- enables
  autonomous repoint requests for exceptionally
  bright bursts that occur outside LAT FOV for
  high-energy afterglow studies (an important
  question from EGRET)
• GLAST observatory provides burst alerts to the
  ground.

Simulated GBM and LAT response to time-integrated
flux from bright GRB 940217 Spectral model
parameters from CGRO wide-band fit 1 NaI (14º)
and 1 BGO (30º)
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GLAST MISSION ELEMENTS
GLAST MISSION ELEMENTS
Large Area Telescope GBM
m

sec
GPS

-

Telemetry 1 kbps
GLAST Spacecraft

TDRSS SN S Ku
DELTA 7920H


S
-
-

GN

LAT Instrument Operations Center
White Sands
Schedules
HEASARC GSFC
Archive
Mission Operations Center (MOC)
GLAST Science Support Center
Schedules
GBM Instrument Operations Center
GRB Coordinates Network
Alerts
Data, Command Loads
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The GLAST Science Support Center

• located in Goddards Laboratory for High Energy
  Astrophysics
• SSC responsible for
• supporting the guest investigator program
• the mission timeline (includes support for TOOs,
  commands)
• providing data analysis software to the
  scientific community
• archiving data software in the HEASARC
• supporting (logistically scientifically) the
  Project Scientist, the Science Working Group, and
  the Users Committee
• instrument teams and SSC define and develop the
  analysis software together
• instrument teams manage the software development,
  but SSC staff assists

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GLAST addresses a broad science menu

• Systems with supermassive black holes
  relativistic jets
• Gamma-ray bursts (GRBs)
• Pulsars
• Solar physics
• Origin of Cosmic Rays
• Probing the era of galaxy formation
• Solving the mystery of the high-energy
  unidentified sources
• Discovery! Particle Dark Matter? Other relics
  from the Big Bang?
• Testing Lorentz invariance. New source
  classes

GLAST draws the interest of both the High Energy
Particle Physics and High Energy Astrophysics
communities.
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Features of the gamma-ray sky
diffuse extra-galactic background (flux
1.5x10-5 cm-2s-1sr-1) galactic diffuse (flux
O(100) times larger) high latitude
(extra-galactic) point sources (typical flux from
EGRET sources O(10-7 - 10-6) cm-2s-1 galactic
sources (pulsars, un-IDd)
EGRET all-sky survey (Egt100 MeV)
An essential characteristic VARIABILITY in time!
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3rd EGRET Catalog
GLAST Survey 10,000 sources (2 years)
GLAST Survey 300 sources (2 days)
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Constraints on extragalactic background light
(EBL) from g-ray blazars
photons with Egt10 GeV are attenuated by the
diffuse field of UV-Optical-IR extragalactic
background light (EBL) g g
? e e-
a dominant factor in determining the EBL is the
time of galaxy formation
opaque
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Unidentified Sources
172 of the 271 sources in the EGRET 3rd catalog
are unidentified
EGRET source position error circles are 0.5,
resulting in counterpart confusion. GLAST will
provide much more accurate positions, with 30
arcsec - 5 arcmin localizations, depending on
brightness.
Cygnus region (15x15 deg)
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Gamma-Ray Bursts
GRBs are now confirmed to be at cosmological
distances. The question persists What are
they??
EGRET detected very high energy emission
associated with bursts, including a 20 GeV
photon 75 minutes after the start of a burst
Hurley et al., 1994
Future Prospects GLAST will provide definitive
information about the high energy behavior of
bursts LAT and GBM together will measure
emission over gt7 decades of energy.
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GRBs and instrument deadtime
Distribution for the 20th brightest burst in a
year (Norris et al)
Time between consecutive arriving photons
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GRB 941017

• recent analysis by Gonzalez, et al.

Compare data from EGRET and BATSE Distinct
high-energy component has different time
behavior! What is the high-energy break and
total luminosity? Need GLAST data!
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GLAST Master Schedule
Launch February 2007
First flight hardware deliveries to SLAC for IT
August 2004
LAT ready for Environmental Test July 2005
GBM IT starts September 2004
Observatory IT starts December 2005
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GLAST Exploring Natures Highest Energy
Processes
launch February 2007