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Observations of GRB 100724B with the Fermi Gamma‐Ray Burst Monitor (GBM) find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non‐thermal emission component, but also includes a statistically highly significant thermal spectral contribution [14]. The simultaneous observation of the thermal and non‐thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non‐thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non‐thermal process, or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.

The Large Area Telescope (LAT) instrument on the Fermi mission is revealing the rich spectral and temporal gamma‐ray burst phenomena in the >100 MeV band. The synergy with Fermi’s GBM detectors links these observations to those in the well‐explored 10–1000 keV range; the addition of the >100 MeV band observations brings new hint and new information about burst emission in both the prompt and afterglow phases. In this contribution we describe the prospects for the Fermi Large Area Telescope (LAT) in observing Gamma‐Ray Bursts (GRBs), and some preliminary results. Here we focus our attention on the importance of multi frequencies approach to GRB science during the just began Fermi era.

The Gamma‐Ray Large Area Space Telescope (GLAST), scheduled to be launched in 2007, will provide the capability to observe Gamma‐Ray Bursts (GRB) from 10 keV to more than 300 GeV. The spectral and temporal properties of GRBs above a few GeV are still almost unknown, extending these detections to higher energies with GLAST will have a large impact on our knowledge of the particle acceleration and emission processes occuring within these sources. In this work we review the requirements and the opportunities for good coordination of GLAST with ground‐based telescopes operating above a few tens of GeV, and examine the potential of such simultaneous observations in terms of expected rates of alerts.

The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration., Comment: 12 pages, 5 figures; submitted proceeding for GRB Symposium in Stockholm, Sweden : "Gamma-Ray Bursts: Prospects for GLAST"

Early X‐ray afterglow observations show that X‐ray flares are very common features in GRB light curves. X‐ray flares may reflect long duration central engine activity. The delayed flare photons are expected to interact with relativistic electrons by Inverse Compton giving delayed high energy counterparts that potentially will be detected by GLAST LAT, which could observe GRB from 20 MeV to more than 300 GeV. The nature oh high energy spectral components from GRB detected by EGRET is still debated. Observations with GLAST LAT will give useful information to constrain the origin of X‐ray flares. In this work we simulate a set of possible GeV emitting flares in the context of External Shock model to study the capability of GLAST LAT to detect GeV flares at different intensities and durations.

The GLAST Large Area Telescope (LAT) is the next generation satellite experiment for high‐energy gamma‐ray astronomy. It employs a pair conversion technique to record photons in the energy range from 20 MeV to more than 300 GeV. The LAT will follow the steps from its predecessor EGRET (1991–2000), and will explore the high‐energy gamma‐ray sky with unprecedented capabilities. The observation of Gamma‐Ray Bursts is one of the main science goal of the LAT: in this contribution we compute an estimation of the LAT sensitivity to GRB, adopting a phenomenological description of GRBs, where the high‐energy emission in GRB is obtained extrapolating the observed BATSE spectrum up to LAT energies. The effect of the cosmological attenuation is included. We use the BATSE current catalog to build up our statistics.

The Gamma‐ray Large Area Space Telescope (GLAST) will observe the gamma‐ray sky in the MeV and GeV energy range. It will detect a number of gamma‐ray bursts (GRBs) every year, depending on their emission at high energies, which is still unknown. GLAST will be the first instrument observing GRBs at energies above 20 GeV. A systematic study prior to launch, which is foreseen for 15 November 2007, was the GLAST Data Challenge 2 (DC 2). For GLAST DC 2 two month of data taking were simulated. Based on these simulations the GRB Working Group performed systematic studies of the performance of GLAST in observing GRBs. These studies included the spectral analysis of the prompt emission, a position fit of the GRB, and the search for prompt and afterglow emissions in the LAT data.

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in fall of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT) is a pair conversion telescope built with a high precision silicon tracker, a segmented CsI electromagnetic calorimeter and a plastic anticoincidence shield. The LAT will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly successful predecessor EGRET. LAT will observe Gamma-Ray Bursts (GRB) in an energy range never explored before; to tie these frontier observations to the better-known properties at lower energies, a second instrument, the GLAST Burst Monitor (GBM) will provide important spectra and timing in the 10 keV to 30 MeV range. We briefly present the instruments onboard the GLAST satellite, their synergy in the GRB observations and the work done so far by the collaboration in simulation, analysis, and GRB sensitivity estimation.

Gamma‐Ray Burst (GRB) prompt emission can, for specific conditions, be so powerful and short‐pulsed to strongly influence any surrounding plasma. In this paper, we briefly discuss the possibility that a very intense initial burst of radiation produced by GRBs satisfy the intensity and temporal conditions to cause stochastic wake‐field particle acceleration in a surrounding plasma of moderate density. We consider a simple but realistic GRB model for which particle wake‐field acceleration can first be excited by a very strong low‐energy precursor, and then be effective in producing the observed prompt X‐ray and gamma‐ray GRB emission.

Especially in the framework of Quantum Gravity, it is theoretically possible that photons of different energy propagate at different velocity. Gamma‐ray Bursts (GRBs), due to their large distances and rapid variability in a broad energy band, are perhaps the best astronomical sources in which to measure any such dispersion over cosmological distances. GLAST will detect several GRBs per year at GeV energies, where the effect may be detectable. We address problems of optimal sensitivity and discrimination against energy‐dependent effects intrinsic to GRB emission, using simulated data and new unbinned lag‐detection algorithms.

The Gamma‐ray Large Area Space Telescope (GLAST) is the next generation satellite for high energy astronomy. The flight hardware production is now complete, the sixteen towers have been integrated into the flight grid and the ACD is already placed onsite. The detector will now be integrated with the spacecraft in the next few months. GLAST will be launched in 2007 and it will cover the energy range from 10 keV to more than 300 GeV. Inspiring ourself to the huge explosion observed the 4th September of 2005 by the Swift mission, 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).

The GLAST Large Area Telescope (LAT) is the next generation satellite experiment for high‐energy gamma‐ray astronomy. It is a pair conversion telescope built with a plastic anticoincidence shield, a segmented CsI electromagnetic calorimeter, and the largest silicon strip tracker ever built. It will cover the energy range from 30 MeV to 300 GeV, shedding light on many issues left open by its predecessor EGRET. One of the most exciting science topics is the detection and observation of gamma‐ray bursts (GRBs). In this paper we present the work done so far by the GRB LAT science group in studying the performance of the LAT detector to observe GRBs. We report on the simulation framework developed by the group as well as on the science tools dedicated to GRBs data analysis. We present the LAT sensitivity to GRBs obtained with such simulations, and, finally, the general scheme of GRBs detection that will be adopted on orbit.

Theoretical models, especially within the framework of Quantum Gravity, allow for the possibility of a velocity dispersion effect for photons of different energies traveling cosmological distances. Due to their fine‐scale time structure and their broad band emission, that is accurately modeled in this work, Gamma Ray Bursts could be good probes of such effect. GLAST will detect several GRBs per year at high energy where the effect could be detectable.