Temporal Evolution of Pair Attenuation Signatures in Gamma-Ray Burst Spectra
Temporal Evolution of Pair Attenuation Signatures in Gamma-Ray Burst Spectra
复制标题
DOI：
10.1086/506960
复制
发表时间：
2006-06
期刊：
影响因子：
--
通讯作者：
M. Baring
中科院分区：
文献类型：
--
作者：
M. Baring
康普顿伽马射线天文台上的白鹭实验对少数伽马射线暴(GRB)进行了高于100 MeV的实验，获得的光谱没有任何迹象表明存在任何光谱衰减，这可能会阻止探测到更高能量的爆发。随着在过去几年中发现了光学余辉和与之对应的爆发，从而能够确定这些源的显著红移，预计对于许多、如果不是大多数的爆发，在30 MeV至300 GeV的伽马射线大面积空间望远镜(GLAST)能带内将出现严重的光谱衰减。本文探讨了ERRET/GLAST波段爆发光谱特性随时间变化的预期，重点研究了在光源内部产生的光子对的衰减如何产生不同的光谱特征。光谱破裂的能量和相关的光谱指数提供了有价值的信息，这些信息限制了给定时刻伽玛暴外流的整体洛伦兹因子。此外，由于宇宙背景场的介入，内部衰减存在的独特的时间行为很容易与外部吸收区分开来。这些特征为空间硬伽马实验(如GLAST)和地面切伦科夫望远镜确定了明显的观测目标，并强烈影响了300 MeV以上爆发的可观测性。
The spectra obtained above 100 MeV by the EGRET experiment aboard the Compton Gamma Ray Observatory for a handful of gamma-ray bursts (GRBs) have given no indication of any spectral attenuation that might preclude detection of bursts at higher energies. With the discovery of optical afterglows and counterparts to bursts in the last few years, enabling the determination of significant redshifts for these sources, it is anticipated that profound spectral attenuation will arise in the Gamma-Ray Large Area Space Telescope (GLAST) energy band of 30 MeV to 300 GeV for many, if not most, bursts. This paper explores time-dependent expectations for burst spectral properties in the EGRET/GLAST band, focusing on how attenuation of photons by pair creation internal to the source generates distinctive spectral signatures. The energy of spectral breaks and the associated spectral indices provide valuable information that constrains the bulk Lorentz factor of the GRB outflow at a given time. Moreover, the distinct temporal behavior that is present for internal attenuation is easily distinguished from extrinsic absorption due to intervening cosmic background fields. These characteristics define palpable observational goals for both spaced-based hard gamma-ray experiments such as GLAST, and ground-based Cerenkov telescopes, and strongly impact the observability of bursts above 300 MeV.