# Presentation: 652245

## High Redshift Gamma-Ray Bursts observed by GLAST

*Abstract*
- 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).

- Hunting GRBs: the GLAST Burst Monitor

**12 Sodium Iodide **
**(NaI)**
** ****Scintillation Detectors**

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

- LAT

- LAT

**2 Bismuth Germanate **
**(BGO)**
** ****Scintillation Detectors**

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

**On 2005 September 4 at 01:51:44 UT: “Detection of a huge explosion in the early Universe”, ***Cusmano et al., astro-ph/0509737 *

- _Redshift_:      6.3
- _BAT Fluence_: 5.4 x 10-6 erg/s
- _Duration (BAT_) ~ 500 s
- _E__peak_  > 150 keV (1+z) ~ 1 MeV
- 3-4 main peaks in the BAT light curve
- _Low energy spectral index_ ~ 1.2

**Nicola Omodei, INFN Pisa, Italy  **
_**nicola.omodei@pi.infn.it**_
**o*****n behalf of the GLAST LAT GRB Science Group and of the GLAST LAT collaboration***

- _GRB simulation:_
**A. Spectrum**: parameterized with a ‘Band’ model (Band et al. 1993)
**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. 2000)
**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 known.
- From the BAT specs, an upper limit for the Ep is provided.
- For GRB, typically, the high energy spectral index is around 2.25
**Two identical GRBs are simulated:**
**One at ‘rest frame’ (z~0)**
**One at z = 6.3**
**Dependence on redshift:**
- Shift of the spectrum at low energy
- “Stretch” of Light curve
**EBL absorption **due to the interaction of high energy photons with the Extragalactic Background Light

- _Conclusions:_
**Test of the full simulation chain: from the simulation of astronomical flux to the analysis of data.**
**Redshift dependence include in the GRB model**
**EBL absorption provided by Luis C. Ryes & Julie McEnery available to GRB models!**
**GLAST will be able to see High Redshift objects!**
**GRB050904 was faint and only few photons are detectable by the LAT.**
**GBM constrain the spectral index at high energy and LAT data can be used to study the cutoff!**
***Refinement on the simulation will include: ***
*Better representation of SWIFT bursts.*
*Better representation of the analytical IRF for simple estimations.*
*Analysis tools for studying the high energy cut-off in case of few photons*.