High Redshift Gamma-Ray Bursts observed by GLAST

High Redshift Gamma-Ray Bursts observed by GLAST

High Redshift Gamma-Ray Bursts observed by GLAST
Nicola Omodei, INFN Pisa, Italy
[email protected]
on behalf of the GLAST LAT GRB Science Group and of the GLAST LAT collaboration
The Gamma-ray Large Area Space Telescope (GLAST) is the next generation satellite for high energy astronomy. It will be launched in 2007 and it will cover the energy range from 10 keV to 300 GeV. Inspiring
our self to the huge explosion observed the 4th September of 2005 by the mission Swift, we use the full simulation chain developed by the GLAST collaboration to simulate an high-redshift Gamma-Ray Burst,
combining all the information available in literature on GRB 050904 with some assumptions, especially for the high energy emission. Our simulation takes care both of the effect of the cosmological expansion on
the spectra and on the light curve, as well as the absorption of radiation by photon-photon interaction with the
Extragalactic Background Light (EBL).

GLAST/LAT scientific performance

The Heart of GLAST: Large Area Telescope
LAT: array of 16
identical towers
Each tower with a
tracker, a calorimeter
and a DAQ.
Surrounded by finely
segmented ACD






DAQ Electronics

The GLAST mission:
Launch Vehicle :
Launch Location:
Orbit Altitude:
Orbit Inclination:
Orbit Period:
Launch Date:

Delta II 2920-10H
Kennedy Space Center
565 Km
28.5 degrees
95 Minutes
Late 2007

Tracker/Converter (TKR):
Silicon strip detectors (single sided, each
layer is rotated by 90 degrees with respect
to the previous one).
W conversion foils.
~80 m2 of silicon (total).
~106 electronics chans.
High precision tracking, small dead time.


Calorimeter (CAL):
1536 CsI crystals.
8.5 radiation lengths.
Shower profile (leakage correction)








F.o.V.: 2.4 sr
Intrinsic resolution of the tracker

Anti-Coincidence (ACD):
Segmented (89 tiles).
Self-veto @ high energy limited.
0.9997 detection efficiency (overall).


Full Tkr


Hunting GRBs: the GLAST Burst Monitor On 2005 September 4 at 01:51:44 UT: Detection of a huge

12 Sodium Iodide
Scintillation Detectors



Energy range: ~10 keV to 1
Major Purposes
Provide low-energy spectral
coverage in the typical GRB
energy regime over a wide
Provide rough burst
locations over a wide FoV

GRB simulation:
A. Spectrum: parameterized
with a Band model (Band et al.
B. Light curve: universal pulse
shape (Norris et al. 1996)
C. Pulse width: depends on the
energy as W(E)~E-0.4
D. Parameters are sampled from
the observed BATSE
distributions (Preece et al.
E. The fluence is normalized in
the BATSE energy range.
The flux is extrapolated at LAT
energies: photons are
sampled from the N(E,t)
Simulation strategy:
From the observation the
fluences the durations and the
low energy spectral index are
From the BAT specs, an upper
limit for the Ep is provided.
For GRB, typically, the high
energy spectral index is around
Two identical GRBs are
One at rest frame (z~0)
One at z = 6.3
Dependence on redshift:
Shift of the spectrum at low
Stretch of Light curve
EBL absorption due to the
interaction of high energy
photons with the Extragalactic
Background Light

2 Bismuth Germanate
Scintillation Detectors

Energy range: ~150 keV to
30 MeV
Major Purpose
Provide high-energy
spectral coverage to
overlap LAT range over a
wide FoV

explosion in the early Universe, Cusmano et al., astro-ph/
BAT Fluence: 5.4 x 10-6 erg/s
Duration (BAT) ~ 500 s
Epeak > 150 keV (1+z) ~ 1 MeV
3-4 main peaks in the BAT light
Low energy spectral index ~ 1.2

GRB Frame (z~0)

GLAST Frame z~6.3
Simple simulation of the SWIFT/BAT signal:
Assuming an effective area 2000 cm2 and a
background 1000 counts/s

Test of the full simulation
chain: from the simulation of
astronomical flux to the
analysis of data.
Redshift dependence
include in the GRB model

Simple simulation of the CGRO/BATSE and of
the GLAST/GBM signal. The effective area of
BATSE is 2000 cm2 with different backgrounds
in different channels.

EBL absorption provided by
Luis C. Ryes & Julie
McEnery available to GRB

For GBM is assumed an effective area of 750
cm2 and a Background of 200 counts per bin.

GLAST will be able to see
High Redshift objects!

Analytical light curve a LAT energies
Pulses are narrower at higher energies, and
peak before!

GRB050904 was faint and
only few photons are
detectable by the LAT.

Analytical integrated spectrum
N(e),E N(e), e2N(e)

GBM constrain the spectral
index at high energy and
LAT data can be used to
study the cutoff!

The expectation for GBM, and LAT detectors
are also plots with symbols.
The effect of the cosmological expansions are
No EBL absorption is included here!
Complete simulation
Rest Frame spectrum
No absorption!

LAT: each photon is folded with the IRF
(Aeff, Edisp, PSF)
EBL absorption is included
Simulated LAT FITS files are obtained
GBM: A series of fluxes is folded with the IRF
for each GBM detectors
Simulated GBM FITS files are obtained
The set of files are combined and a spectral
analysis is performed, as with real data !

High Energy cut-off
due to EBL

Refinement on the
simulation will include:
Better representation of
SWIFT bursts.
Better representation of the
analytical IRF for simple
Analysis tools for studying the
high energy cut-off in case of
few photons.

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