A Photosphere-Internal Shock Model of Gamma-Ray Bursts: Case Studies of Fermi-LAT Bursts - Astrophysics > High Energy Astrophysical PhenomenaReport as inadecuate




A Photosphere-Internal Shock Model of Gamma-Ray Bursts: Case Studies of Fermi-LAT Bursts - Astrophysics > High Energy Astrophysical Phenomena - Download this document for free, or read online. Document in PDF available to download.

Abstract: Radially inhomogeneous gamma-ray burst GRB jets release variablephotospheric emission and can have internal shocks occurring above thephotosphere. We generically formulate a photospheric emission model of GRBsincluding Compton up-scattered photospheric UP emission off the electronsand positrons in the internal shocks, and find that the photospheric emissionmay correspond to the traditional Band component at <~1 MeV and the UPemission to the high-energy emission observed by Fermi-LAT for some GRBs at >~10 MeV. The two components can be separate in the spectrum in some cases or canmimic a smooth broad Band spectrum in other cases. We apply our formulation tothe well-studied long and short LAT GRBs, GRB 080916C, GRB 090902B, and GRB090510, and typically find reasonable parameters for fitting the time-binnedspectra, although fine tuning of several parameters is required. The observeddelays of the high-energy emission with respect to the MeV emission which arelarge compared to the variability times are unlikely to be due to simplekinematic effects of a non-evolving jet. These delays may be attributed to thetemporal evolution of the physical parameters of the jet, and thus the delaytimescales could provide a potential tool for investigating the structures ofGRB jets themselves and their progenitors. The difference of the delaytimescales of long and short GRBs inferred from the Fermi data might be due tothe differences in the progenitors of long and short GRBs. Some otherproperties and consequences of this model are discussed, including temporalcorrelations among the prompt optical, the soft X-ray, and the distincthigh-energy component as well as the Band component.



Author: Kenji Toma, Xue-Feng Wu, Peter Meszaros

Source: https://arxiv.org/



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