Ackermann 2012 LAT和GBM联合谱分析，得到cutoff的能量

主要内容:
联合谱分析，但是LAT大部分只有光子数的上限，得到的一般可以给出一个cutoff的能量。他们用这个能量以及光子光子湮灭假设来限制Lorentz因子。

精彩摘抄:

文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1201.3948)

· References in the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		Constraining the High-Energy Emission from Gamma-ray Bursts with Fermi
Authors:		The Fermi-LAT Collaboration; The Fermi-GBM Collaboration
Publication:		eprint arXiv:1201.3948
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		Contact Authors: D. Kocevski, kocevski@stanford.edu; J. Chiang, jchiang@slac.stanford.edu; V. Connaughton, connauv@uah.edu; M. Briggs, michael.briggs@nasa.gov; E. Moretti, moretti@particle.kth.se; 52 page, 13 figures, submitted to ApJ
Bibliographic Code:		2012arXiv1201.3948T

Abstract

We examine 288 GRBs detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field-of-view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We compare these limits with the fluxes that would be expected from extrapolations of spectral fits presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the {\nu}F{\nu} spectra (Epk). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above Epk than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cut-off in their high-energy spectra, which if assumed to be due to {\gamma}{\gamma} attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. All of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT- detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)