Transcript The GLAST Burst Monitor (GBM)

gammaray.msfc.nasa.gov/GBM
Abstract
The GLAST Burst Monitor (GBM)
R. M. Kippen, M. S. Briggs, W. S. Paciesas, R. D. Preece
UAH/NSSTC
C. A. Meegan, G. J. Fishman, C. Kouveliotou
NASA/NSSTC
G. G. Lichti, V. Schönfelder, A. von Kienlin, R. H. Georgii, R. Diehl
MPE
The study of gamma-ray bursts (GRBs) is one of the primary scientific objectives of the
Gamma-ray Large Area Space Telescope (GLAST) mission. With its high sensitivity to prompt
and extended 20 MeV to 300 GeV burst emission, GLAST's Large Area Telescope (LAT) is
expected to yield significant progress in the understanding of GRB physics. To tie these
breakthrough high-energy measurements to the known properties of GRBs at lower energies,
the GLAST Burst Monitor (GBM) will provide spectra and timing in the 10 keV to 25 MeV energy
range. The GBM will also have the capability to quickly localize burst sources to ~20° over
more than half the sky, allowing the LAT to re-point at particularly interesting bursts which
occur outside its field of view. With combined LAT/GBM measurements GLAST will be able to
characterize the spectral behavior of many bursts over six decades in energy. This will allow
the unknown aspects of high-energy burst emission to be explored in the context of wellknown low-energy properties. In this paper, we present an overview of the GBM instrument,
including its technical design, scientific goals, and expected performance.
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April, 2001
The GLAST Mission
 NASA’s next major gamma-
ray mission
 Follow-on to successful
Compton-EGRET
 Primary scientific mission:
high-energy gamma-ray
astronomy (20 MeV to >300
GeV), including:
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Active Galactic Nuclei
Diffuse Galactic & Cosmic
Emission
Gamma-ray bursts
Solar flares
Pulsars, Neutron stars, BHCs
Molecular clouds, SNR
Dark matter, particle physics...
 5-year mission starting 2006
 International participation
Gamma 2001
 Primary instrument:
Large Area Telescope
(LAT) ~95% of total instrument
resources
 Secondary instrument:
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GLAST Burst Monitor
April, 2001
Gamma-Ray Bursts
Properties
 Isotropic & inhomogeneous spatial
distribution
 Fast, chaotic, variability
 Bimodal prompt duration distribution
 Characteristic non-thermal, evolving
gamma-ray spectra extending E > GeV
 Fading multiwavelength afterglow
 One case of prompt optical emission
 Measured redshifts z ~ 1–5
 Associated with “Normal” host galaxies
 Eg ~1052-53 erg
 Wide luminosity distribution
 Most energetic explosions in the universe
 Extreme physics, highly relativistic outflow
 Cosmological probes of early universe
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April, 2001
GLAST and Gamma-Ray Bursts (Present)
 Little is known about GRB emission
in the >50 MeV energy regime
Composite spectrum of 5 EGRET Bursts
Dingus et al. 1997
 EGRET detected ~5 high-energy
bursts, but suffered from:
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Small field of view (~40°), so few
bursts were detected
Small effective area (~1000 cm2), so
few detected photons per burst
Large deadtime (~100 ms/photon),
so few prompt photons were
detected
 Prompt GeV emission with no highenergy cutoff (combined with
rapid variability) implies highly
relativistic bulk motion at source:
G > 102–103
Extended/Delayed
emission
 Extended or delayed GeV emission
may require more than one
emission mechanism
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No evidence
of cutoff
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Hurley et al. 1994
April, 2001
GLAST and Gamma-Ray Bursts (Future)
 The GLAST LAT will have:
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Large ~2 sr field of view, so more
detected bursts (~50–100/yr)
>10 EGRET effective area, so
more photons per burst
105 lower deadtime, so more
detected prompt photons
Improved sensitivity E>10 GeV, for
better locations and spectral
range
~5 better angular resolution, for
arc-min GRB locations and better
afterglow sensitivity
On-board computing for providing
rapid GRB locations to afterglow
observers
GLAST LAT
Baring 1996
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GLAST LAT
GRB Location Accuracy
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Norris et al. 1998
 The GLAST LAT will not have:
Sensitivity <10 MeV, where there is
the most knowledge of GRBs
Sensitivity outside its FoV
Fast trigger for weak bursts
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April, 2001
Role of the GLAST Burst Monitor (GBM)
 LAT will provide ground-breaking new GRB observations, but it will be
difficult to evaluate them in the context of current GRB knowledge
 GBM will enhance GLAST GRB
science by providing low-energy
context measurements with high
time resolution
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Improved GBM+LAT wide-band
spectral sensitivity
Compare low-energy vs. highenergy temporal variability
Continuity with current GRB
knowledge-base (GRO-BATSE)
 GBM will provide rapid GRB timing &
location triggers w/FoV > LAT FoV
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Improve LAT sensitivity and response
time for weak bursts
Re-point GLAST/LAT at particularly
interesting bursts for afterglow
observations
Provide rapid locations for
ground/space follow-up
observations & IPN timing
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April, 2001
GBM Collaboration
National Space Science & Technology Center
University of Alabama
in Huntsville
NASA
Marshall Space Flight Center
Michael Briggs
Marc Kippen
William Paciesas
Robert Preece
Charles Meegan (PI)
Gerald Fishman
Chryssa Kouveliotou
On-board processing, flight software, systems
engineering, analysis software, and management
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Max-Planck-Institut für
extraterrestrische Physik
Giselher Lichti (Co-PI)
Andreas von Keinlin
Robert Georgii
Volker Schönfelder
Roland Diehl
Detectors, power supplies,
calibration, and analysis software
April, 2001
Instrument Requirements
Top-Level GBM Instrument Requirements
Parameter
Requirement
Goal
BATSE
Energy range
10 keV – 25 MeV
5 keV – 30 MeV
Energy resolution
20% FWHM at 511 keV
—
10 keV – 1.8 MeV (LAD)
15 keV – >30 MeV (SD)
~20% FWHM at 511 keV
Time resolution
10 microsecond
2 microsecond
2 microsecond
On-board GRB
locations
20º accuracy (1 radius)
within 2 seconds
10º within 1 second
None
Rapid ground GRB 5º accuracy (1 radius)
locations
within 5 seconds
3º within 1 second
Final GRB
locations
—
Field of view
3º accuracy (1 radius)
within 1 day
0.5 photons cm-2 s-1 (peak
flux, 50–300 keV)
8 steradians
10º within 5 seconds;
3º within 20 minutes
3º within few days
Deadtime
<10 s/count
<3 s/count
GRB sensitivity
0.3 photons cm-2 s-1 (peak 0.1 photons cm-2 s-1 (peak
flux, 50–300 keV)
flux, 50–300 keV)
10 steradians
12.6 (4) steradians
~10 s/count
 Available Resources:
Mass: <70 kg
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Power: <50 Watts (average)
–9–
Cost to NASA: ~$5M
April, 2001
Instrument Design: Major Components
Data Processing
Unit (DPU)
12 Sodium Iodide (NaI)
Scintillation Detectors
Characteristics
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5-inch diameter, 0.5-inch thick
One 5-inch diameter PMT per Det.
Placement to maximize FoV
Thin beryllium entrance window
Energy range: ~5 keV to 1 MeV
Major Purposes
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Provide low-energy spectral
coverage in the typical GRB energy
regime over a wide FoV
Provide rough burst locations over a
wide FoV
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Characteristics
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Analog data acquisition electronics
for detector signals
CPU for data packaging/processing
Major Purposes
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Central system for instrument
command, control, data processing
Flexible burst trigger algorithm(s)
Automatic detector/PMT gain
control
Compute on-board burst locations
Issue r/t burst alert messages
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2 Bismuth Germanate (BGO)
Scintillation Detectors
Characteristics
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5-inch diameter, 5-inch thick
High-Z, high-density
Two 5-inch diameter PMTs per Det.
Energy range: ~150 keV to 30 MeV
Major Purpose
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Provide high-energy spectral
coverage to overlap LAT range over
a wide FoV
April, 2001
Instrument Design: Functional Diagram
1 of 12
PMT
Science data
HVPS
Command
Data
Processing
Unit (DPU)
Cmd/Resp
PPS
Spacecraft
Interface
…
Ancillary Data
1 of 2
PMT
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BGO
LVPS
PMT
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Power
April, 2001
Prototype Detectors
Prototype detectors being tested at MPE
Prototype NaI Detector
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Prototype BGO Detector
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April, 2001
Detector Placement Concept
Low-Energy NaI(Tl)
Detectors (3 of 12)
LAT
High-Energy BGO
Detector (1 of 2)
Top View
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Side View
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April, 2001
Expected Detector Performance
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April, 2001
Expected Detector Performance
Detector Response Matrices (DRMs)
from GEANT3 Monte Carlo Simulations
Photon Energy (keV)
10
10
10
10
Estimated Background from
Simulations and BATSE Extrapolations
4
3
2
NaI DRM (cm2)
1
0.0
10.0
20.0
30.0
znai_dat
10
1
10
2
10
3
10
4
Photon Energy (keV)
Measured Energy (keV)
10
10
10
4
3
2
BGO DRM (cm2)
0.0
10
2
10.0
10
20.0
zbgo_dat
3
30.0
10
40.0
4
Measured Energy (keV)
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April, 2001
GRB Spectral Performance (GBM+LAT)
 Simulated GBM and LAT
response to time-integrated
flux from bright GRB 940217
 Spectral model parameters
from CGRO wide-band fit
 1 NaI (14 º) and 1 BGO (30 º)
 Baseline 8000 cm2 LAT @ 30º
(actual LAT now expected to be ~10000 cm2)
 Good spectral response over
5.3 decades in energy!
 In addition to providing lowenergy parameters, combined
fit yields better constraints on
high-energy power-law index
than LAT-only fit
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April, 2001
Time-Resolved Spectroscopy Performance
 Simulation of bright
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GRB~990123
Model parameters
taken from BATSE fits
Same detector
response as previous
example
GBM detectors can
easily measure
evolution of low-energy
spectral parameters
LAT alone cannot
detect evolution of
high-energy index b
LAT+GBM can detect
evolution of b
April, 2001
GRB Sensitivity & Location Performance
 Trigger sensitivity assumes BATSElike trigger (>5 in 2 or more NaI
detectors)
 Total on-board burst trigger rate
150–225 yr-1, depending on GLAST
pointing schedule
Map of GRB Statistical Location
Error for Peak Flux = 1 ph s-1 cm-2
 Statistical GRB location errors:
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~9º for 1 ph cm-2 s-1 burst (~100 yr-1)
~1.5º for 10 ph cm-2 s-1 burst (~10 yr1)
April, 2001
Data Types
 Continuous data for weak (post-facto) burst
 Multiple data types to
maximize science return for
given telemetry allocation
ITIME
Nominal
Integration
Time
16 ms
Number of
Energy
Channels
8
ISPEC
10 min
128
CTIME
0.256 s
8
Internal use by trigger and
burst parameter software
Internal use by AGC and burst
parameter software
Continuous science telemetry
CSPEC
8.192 s
128
Continuous science telemetry
CHK
TTE
TRIGDAT
Deadtime
PROGDAT
multiplexed Not applicable
2.0 s / sensor
Individually
128
time-tagged
Not
Not applicable
applicable
16 ms
Not applicable
Not
applicable
Not applicable
Use
Internal D ata (ITIME & ISPEC )
Detector Count Rate
Data Type
triggering & background estimation
 Triggered data for best possible temporal &
spectral resolution during bursts
 Length of trigger data readout computer
controlled
Typical Duration
0.1–100 s
Burst
Trigger
Time
Trigger D ata (TTE & TR IGD AT)
Pre-Trigger TTE
(all detectors)
Post-Trigger TTE
(s/w selected detectors)
Continuous housekeeping
TTE Readout & Telemetry
via HSSDB
TRIGDAT1
Triggered science telemetry
TRIGDAT2 … TRIGDATn
TRIGDAT Priority Telemetry
via CTDB
Triggered priority science
telemetry
Goal: triggered science
telemetry
Program memory downloads
Continuous Scienc e Data (CTIME, CSPEC)
Continuous Houseke eping Da ta (C HK)
Continuous Telemetry
via HSSDB
Continuous Telemetry
via CTDB
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April, 2001
Mission/Instrument Operations
LAT
Instrument
Operations
Center (IOC)
GLAST
Mission
Operations
Center (MOC)
GLAST
Science
Operations
Center (SOC)
Science
User Community
GBM
Instrument
Operations
Center (IOC)
• GBM/LAT commands
• GBM/LAT monitoring
• Compute rapid GRB
locations LAT/GBM
• Distribute GRB alerts
via GCN
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• Archive processed
science data
• Distribute data to
user community
• Monitor instrument operation
and performance
• Flight s/w updates
• Generate Inst. commands
• Routine science processing
– 20 –
• Including Inst. Team
members
• Scientific data analysis
• Including final GRB
locations and joint
GBM/LAT spectral &
timing analysis
April, 2001