Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session B7: Gamma-Ray Bursts and GLAST |
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Sponsoring Units: DAP Chair: Julie McEnery, Goddard Space Flight Center Room: Hyatt Regency Dallas Pegasus A |
Saturday, April 22, 2006 10:45AM - 10:57AM |
B7.00001: Gamma-Ray Bursts Observations with GLAST Nicola Omodei, Charles Meegan, Valerie Connaughton, Neil Gehrels, Jay Norris The Gamma-Ray Large Area Space Telescope (GLAST), scheduled to be launched in 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope, the heart of GLAST, is a pair conversion telescope built with a plastic anticoincidence shield, a segmented CsI electromagnetic calorimeter, and the largest silicon strip tracker ever built. LAT will survey the sky in the energy range between 30 MeV to greater than 300 GeV, exploring the high energy gamma-ray sky, shedding light on many issues left open by its ancestor EGRET. The LAT’s wide field of view ($>$2 sr), large effective area and low deadtime combine to provide excellent high-energy gamma-ray observations of GRB. To tie these frontier high-energy 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 25 MeV range. We briefly present the instruments onboard the GLAST satellite, their synergy in the GRB observation and the work done so far by the collaboration in simulation, analysis, and GRB sensitivity estimation. [Preview Abstract] |
Saturday, April 22, 2006 10:57AM - 11:09AM |
B7.00002: Rapid Spectral Variability of GRBs. A Puzzle Solved? Mikhail Medvedev Millisecond spectral variability of prompt GRBs, such as the so-called ``tracking behavior'' and correlation of the soft photon index $\alpha$ and the observed flux, does not have a satisfactory explanation for some fifteen years. We demonstrate that the spectral variability of GRBs is an inherent property of radiation emitted by electrons from highly anisotropic small- scale magnetic fields, generated at internal shocks. We interpret the flux-$\alpha$ correlation and the tracking pattern as a combined effect of temporal variation of the shock viewing angle and relativistic aberration of an instantaneously illuminated, thin shell. The model predicts that hard (e.g., synchrotron violating, with $\alpha>-2/3$) spectra result from a shock patch close to the line of sight and that they are associated with the onset of a sub-pulse. The spectral softening occurs on the $R/c\Gamma^2$ time-scale. The model also naturally explains why the peak of the distribution of $\alpha$ is at $\alpha\sim-1$. The presence of a low-energy break in the jitter spectrum at oblique angles also explains the appearance of a soft X-ray component in some GRBs. We emphasize that our theory is based solely on the first principles and contains no ad hoc assumptions. [Preview Abstract] |
Saturday, April 22, 2006 11:09AM - 11:21AM |
B7.00003: TeV Gamma Ray Astronomy and GLAST Elliott Bloom, Lester Miller The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) will have sensitivity to gamma rays beyond 100 GeV, for the first time providing a data set overlapping with the energy range of ground based gamma ray instruments. The next generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), including MAGIC, HESS, and VERITAS, will therefore be complemented by the GLAST survey dataset. The GLAST large field of view will provide a survey of the high energy sky, providing the IACTs with a large number of potential sources to observe. In addition, GLAST observations can be used to cross-calibrate the IACT energy scale and flux measurements, potentially reducing their systematic uncertainty. Together GLAST and IACTs will be able to probe gamma ray spectra from 20 MeV to the multi - TeV regime. [Preview Abstract] |
Saturday, April 22, 2006 11:21AM - 11:33AM |
B7.00004: Overview of the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT): Description and Performance Goals Tracy Usher The Gamma-ray Large Area Space Telescope, GLAST, is an orbital mission in the final stages of construction designed to measure the cosmic gamma-ray flux in the energy range 20 MeV to $>$300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV.~ With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena. This talk will present an overview of the GLAST LAT instrument design and construction, including estimates of the performance that demonstrate the power of this new high-energy gamma-ray physics tool. [Preview Abstract] |
Saturday, April 22, 2006 11:33AM - 11:45AM |
B7.00005: Onboard filtering and science processing in GLAST Frederick Kuehn Launching in 2007, the Gamma-ray Large Area Space Telescope (GLAST), will measure the spectrum of gamma-rays from 20 MeV to $>$ 300 GeV using the Large Area Telescope (LAT). As photons enter the LAT, they produce electron-positron pairs that traverse a tracker consisting of planes of silicon strip detectors and a segmented CsI calorimeter. Charged Cosmic Rays (CR's) are vetoed by an Anti-Coincidence Detector. CR backgrounds are far larger than the gamma-ray flux. Onboard, the LAT uses hardware triggers that are efficient for determining gamma-ray candidate events, along with subsequent software filters that reduce the data volume by an additional factor of $\sim $10 to meet the downlink requirements. Incorporated in the onboard software are algorithms for identifying transients such as Gamma Ray Bursts and flaring states of Active Galactic Nuclei. I will describe the hardware and software trigger algorithms and their impact on event selection and onboard science. [Preview Abstract] |
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