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GLAST Mission:
Gamma-ray Large Area
Space Telescope Status and Science
Opportunities
Peter F. Michelson
Stanford University
peterm@stanford.edu
Outline
• GLAST: An International Science Mission
– Large Area Telescope (LAT)
– GLAST Burst Monitor (GBM)
• Mission Operations Plan
• highlights of science opportunities
• schedule highlights
The GLAST Observatory
two GLAST instruments:
LAT: 20 MeV – >300 GeV
GBM: 10 keV – 25 MeV
Large Area Telescope
(LAT)
GLAST Burst Monitor
(GBM)
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)
Sweden Italy France
Germany USA Japan
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: Energy loss mechanisms:
determine photon direction
clear signature for background rejection
- limitations on angular resolution (PSF)
low E: multiple scattering => many thin layers
high E: hit precision & lever arm
Pair-Conversion Telescope
anticoincidence
shield
• must detect -rays with high efficiency
conversion foil
and reject the much larger (~104:1) flux
particle tracking
of background cosmic-rays, etc.;
detectors • energy resolution requires calorimeter
of sufficient depth to measure buildup
e+ e– calorimeter of the EM shower. Segmentation useful
(energy measurement)
for resolution and background rejection.
Overview of LAT
• Precision Si-strip Tracker (TKR)
18 XY tracking planes. Single-sided
Tracker
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,
ACD e+ e–
robust hardware trigger and software
[surrounds
filters.
4x4 array of
Calorimeter
TKR towers]
Systems work together to identify and measure the flux of cosmic gamma
rays with energy 20 MeV - >300 GeV.
GLAST LAT High Energy Capabilities
• Huge FOV (~20% of sky)
• Broadband (4 decades in energy, including unexplored region > 10 GeV)
• Unprecedented PSF for gamma rays (factor > 3 better than EGRET for E>1 GeV)
• Large effective area (factor > 4 better than EGRET)
• Results in factor > 30-100 improvement in sensitivity
• No expendables long mission without degradation
High energy source sensitivity: all-sky scan mode
100 sec
During the all-sky
survey, GLAST
will have
sufficient
EGRET Fluxes sensitivity after
O(1) day to
- GRB940217 (100sec)
- PKS 1622-287 flare detect (5s) the
1 orbit* - 3C279 flare weakest EGRET
- Vela Pulsar sources.
- Crab Pulsar
- 3EG 2020+40 (SNR Cygni?)
- 3EG 1835+59
- 3C279 lowest 5s detection
- 3EG 1911-2000 (AGN)
1 day^
- Mrk 421
- Weakest 5s EGRET source
*zenith-pointed
^“rocking” all-sky scan: alternating
orbits point above/below the orbit plane
8
GBM Detector
(12) Sodium Iodide (NaI)
Bismuth Germanate (BGO) LAT
Scintillation Detectors
Scintillation Detector
Major Purposes
Major Purpose
– Provide low-energy spectral coverage
– Provide high-energy spectral
in the typical GRB energy regime over
a wide FoV (10 keV – – 25 MeV) to
coverage (150 keV 1 MeV)
– Provide rough burst locations over a
overlap LAT range over a wide
FoV
wide FoV
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;
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)
• 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.
GLAST MISSION ELEMENTS
GLAST MISSIONELEMENTS
GPS • msec Large Area Telescope
& GBM
•
• Telemetry 1 kbps -
GLAST Spacecraft
•
TDRSS SN
DELTA S & Ku
7920H •
•
- S
-
•
GN
•
LAT Instrument White Sands
Schedules Operations Center
Mission Operations GLAST Science Archive HEASARC
Center (MOC) Support Center GSFC
Schedules
GRB GBM Instrument
Coordinates Network Alerts Operations Center
Data, Command Loads
11
The GLAST Science Support Center
• located in Goddard’s 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
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.
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-ID’d)
EGRET all-sky survey (E>100 MeV)
An essential characteristic: VARIABILITY in time!
field of view, and the ability to repoint, important for
study of transients.
3rd EGRET sources
GLAST Survey: ~300Catalog (2 years)
GLAST Survey: ~10,000sources (2 days)
AGN - blazars pulsars
unidentified LMC
Constraints on extragalactic background
light (EBL) from -ray blazars
photons with E>10 GeV are attenuated by the diffuse field of UV-Optical-
IR extragalactic background light (EBL) + e+ + e-
a dominant factor in determining the EBL is the time of galaxy formation
Salamon & Stecker, ApJ 493, 547 (1998)
Chen & Ritz, ApJ (2000)
opaque
No significant attenuation
below 10 GeV
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)
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 >7 decades of energy.
GRBs and instrument deadtime
Distribution for the 20th brightest burst in a year (Norris et al)
LAT will open
a wide window
on the study
of the high
energy
behavior of
bursts.
Time between consecutive arriving photons
GRB 941017
recent analysis by Gonzalez, et al.
Compare data
from EGRET
-18 to 14 sec
and BATSE:
Distinct high-
energy 14 to 47 sec
component
has different
time
behavior! 47 to 80 sec
What is the
high-energy
break and 80-113 sec
total
luminosity?
113-211 sec
Need GLAST
data!
GLAST Master Schedule
Launch:
February 2007
First flight hardware LAT ready for
deliveries to SLAC for Environmental Test:
I&T: August 2004 July 2005
GBM I&T starts:
September 2004
Observatory I&T
starts: December 2005
GLAST: `
Exploring Nature’s Highest Energy Processes
launch: February 2007
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