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Title: PHOTOSPHERE EMISSION FROM A HYBRID RELATIVISTIC OUTFLOW WITH ARBITRARY DIMENSIONLESS ENTROPY AND MAGNETIZATION IN GRBs

Abstract

In view of the recent Fermi observations of gamma-ray burst (GRB) prompt emission spectra, we develop a theory of photosphere emission of a hybrid relativistic outflow with a hot fireball component (defined by dimensionless entropy η) and a cold Poynting-flux component (defined by magnetization σ{sub 0} at the central engine). We consider the scenarios both without and with sub-photospheric magnetic dissipations. Based on a simplified toy model of jet dynamics, we develop two approaches: a 'bottom-up' approach to predict the temperature (for a non-dissipative photosphere) and luminosity of the photosphere emission and its relative brightness for a given pair of (η, σ{sub 0}); and a 'top-down' approach to diagnose central engine parameters (η and σ{sub 0}) based on the observed quasi-thermal photosphere emission properties. We show that a variety of observed GRB prompt emission spectra with different degrees of photosphere thermal emission can be reproduced by varying η and σ{sub 0} within the non-dissipative photosphere scenario. In order to reproduce the observed spectra, the outflows of most GRBs need to have a significant σ, both at the central engine and at the photosphere. The σ value at 10{sup 15} cm from the central engine (a possible non-thermal emission site) ismore » usually also greater than unity, so that internal-collision-induced magnetic reconnection and turbulence (ICMART) may be the mechanism to power the non-thermal emission. We apply our top-down approach to GRB 110721A and find that the temporal evolution behavior of its blackbody component can be well interpreted with a time-varying (η, σ{sub 0}) at the central engine, instead of invoking a varying engine base size r {sub 0} as proposed by previous authors.« less

Authors:
 [1];  [2]
  1. Current address: Department of Astronomy and Astrophysics, Department of Physics, Center for Particle Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
  2. Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154 (United States)
Publication Date:
OSTI Identifier:
22522085
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 801; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BRIGHTNESS; COLLISIONS; COSMIC GAMMA BURSTS; EMISSION SPECTRA; ENTROPY; JETS; LUMINOSITY; MAGNETIC RECONNECTION; MAGNETIZATION; NUCLEAR FIREBALLS; PHOTOSPHERE; RELATIVISTIC RANGE; STAR EVOLUTION; TURBULENCE

Citation Formats

Gao, He, and Zhang, Bing, E-mail: gaohe@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hug18@psu.edu. PHOTOSPHERE EMISSION FROM A HYBRID RELATIVISTIC OUTFLOW WITH ARBITRARY DIMENSIONLESS ENTROPY AND MAGNETIZATION IN GRBs. United States: N. p., 2015. Web. doi:10.1088/0004-637X/801/2/103.
Gao, He, & Zhang, Bing, E-mail: gaohe@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hug18@psu.edu. PHOTOSPHERE EMISSION FROM A HYBRID RELATIVISTIC OUTFLOW WITH ARBITRARY DIMENSIONLESS ENTROPY AND MAGNETIZATION IN GRBs. United States. doi:10.1088/0004-637X/801/2/103.
Gao, He, and Zhang, Bing, E-mail: gaohe@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hug18@psu.edu. Tue . "PHOTOSPHERE EMISSION FROM A HYBRID RELATIVISTIC OUTFLOW WITH ARBITRARY DIMENSIONLESS ENTROPY AND MAGNETIZATION IN GRBs". United States. doi:10.1088/0004-637X/801/2/103.
@article{osti_22522085,
title = {PHOTOSPHERE EMISSION FROM A HYBRID RELATIVISTIC OUTFLOW WITH ARBITRARY DIMENSIONLESS ENTROPY AND MAGNETIZATION IN GRBs},
author = {Gao, He and Zhang, Bing, E-mail: gaohe@physics.unlv.edu, E-mail: zhang@physics.unlv.edu, E-mail: hug18@psu.edu},
abstractNote = {In view of the recent Fermi observations of gamma-ray burst (GRB) prompt emission spectra, we develop a theory of photosphere emission of a hybrid relativistic outflow with a hot fireball component (defined by dimensionless entropy η) and a cold Poynting-flux component (defined by magnetization σ{sub 0} at the central engine). We consider the scenarios both without and with sub-photospheric magnetic dissipations. Based on a simplified toy model of jet dynamics, we develop two approaches: a 'bottom-up' approach to predict the temperature (for a non-dissipative photosphere) and luminosity of the photosphere emission and its relative brightness for a given pair of (η, σ{sub 0}); and a 'top-down' approach to diagnose central engine parameters (η and σ{sub 0}) based on the observed quasi-thermal photosphere emission properties. We show that a variety of observed GRB prompt emission spectra with different degrees of photosphere thermal emission can be reproduced by varying η and σ{sub 0} within the non-dissipative photosphere scenario. In order to reproduce the observed spectra, the outflows of most GRBs need to have a significant σ, both at the central engine and at the photosphere. The σ value at 10{sup 15} cm from the central engine (a possible non-thermal emission site) is usually also greater than unity, so that internal-collision-induced magnetic reconnection and turbulence (ICMART) may be the mechanism to power the non-thermal emission. We apply our top-down approach to GRB 110721A and find that the temporal evolution behavior of its blackbody component can be well interpreted with a time-varying (η, σ{sub 0}) at the central engine, instead of invoking a varying engine base size r {sub 0} as proposed by previous authors.},
doi = {10.1088/0004-637X/801/2/103},
journal = {Astrophysical Journal},
number = 2,
volume = 801,
place = {United States},
year = {Tue Mar 10 00:00:00 EDT 2015},
month = {Tue Mar 10 00:00:00 EDT 2015}
}