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Title: HOT ELECTROMAGNETIC OUTFLOWS. I. ACCELERATION AND SPECTRA

Abstract

The theory of cold, relativistic, magnetohydrodynamic outflows is generalized by the inclusion of an intense radiation source. In some contexts, such as the breakout of a gamma-ray burst (GRB) jet from a star, the outflow is heated to a high temperature at a large optical depth. Eventually it becomes transparent and is pushed to a higher Lorentz factor by a combination of the Lorentz force and radiation pressure. We obtain its profile, both inside and outside the fast magnetosonic critical point, when the poloidal magnetic field is radial and monopolar. Most of the energy flux is carried by the radiation field and the toroidal magnetic field that is wound up close to the rapidly rotating engine. Although the entrained matter carries little energy, it couples the radiation field to the magnetic field. Then the fast critical point is pulled inward from infinity and, above a critical radiation intensity, the outflow is accelerated mainly by radiation pressure. We identify a distinct observational signature of this hybrid outflow: a hardening of the radiation spectrum above the peak of the seed photon distribution, driven by bulk Compton scattering. The non-thermal spectrum-obtained by a Monte Carlo method-is most extended when the Lorentz force dominatesmore » the acceleration, and the seed photon beam is wider than the Lorentz cone of the MHD fluid. This effect is a generic feature of hot, magnetized outflows interacting with slower relativistic material. It may explain why some GRB spectra appear to peak at photon energies above the original Amati et al. scaling. A companion paper addresses the case of jet breakout, where diverging magnetic flux surfaces yield strong MHD acceleration over a wider range of Lorentz factor.« less

Authors:
 [1];  [2]
  1. Department of Physics, University of Toronto, 60 St. George St., Toronto, ON M5S 1A7 (Canada)
  2. Canadian Institute for Theoretical Astrophysics, 60 St. George St., Toronto, ON M5S 3H8 (Canada)
Publication Date:
OSTI Identifier:
22126901
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 767; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COMPTON EFFECT; COSMIC GAMMA BURSTS; GAMMA RADIATION; INCLUSIONS; LORENTZ FORCE; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; PEAKS; PHOTON BEAMS; PHOTONS; RADIATION PRESSURE; RADIATION SOURCES; RELATIVISTIC RANGE; SPECTRA

Citation Formats

Russo, Matthew, and Thompson, Christopher. HOT ELECTROMAGNETIC OUTFLOWS. I. ACCELERATION AND SPECTRA. United States: N. p., 2013. Web. doi:10.1088/0004-637X/767/2/142.
Russo, Matthew, & Thompson, Christopher. HOT ELECTROMAGNETIC OUTFLOWS. I. ACCELERATION AND SPECTRA. United States. https://doi.org/10.1088/0004-637X/767/2/142
Russo, Matthew, and Thompson, Christopher. 2013. "HOT ELECTROMAGNETIC OUTFLOWS. I. ACCELERATION AND SPECTRA". United States. https://doi.org/10.1088/0004-637X/767/2/142.
@article{osti_22126901,
title = {HOT ELECTROMAGNETIC OUTFLOWS. I. ACCELERATION AND SPECTRA},
author = {Russo, Matthew and Thompson, Christopher},
abstractNote = {The theory of cold, relativistic, magnetohydrodynamic outflows is generalized by the inclusion of an intense radiation source. In some contexts, such as the breakout of a gamma-ray burst (GRB) jet from a star, the outflow is heated to a high temperature at a large optical depth. Eventually it becomes transparent and is pushed to a higher Lorentz factor by a combination of the Lorentz force and radiation pressure. We obtain its profile, both inside and outside the fast magnetosonic critical point, when the poloidal magnetic field is radial and monopolar. Most of the energy flux is carried by the radiation field and the toroidal magnetic field that is wound up close to the rapidly rotating engine. Although the entrained matter carries little energy, it couples the radiation field to the magnetic field. Then the fast critical point is pulled inward from infinity and, above a critical radiation intensity, the outflow is accelerated mainly by radiation pressure. We identify a distinct observational signature of this hybrid outflow: a hardening of the radiation spectrum above the peak of the seed photon distribution, driven by bulk Compton scattering. The non-thermal spectrum-obtained by a Monte Carlo method-is most extended when the Lorentz force dominates the acceleration, and the seed photon beam is wider than the Lorentz cone of the MHD fluid. This effect is a generic feature of hot, magnetized outflows interacting with slower relativistic material. It may explain why some GRB spectra appear to peak at photon energies above the original Amati et al. scaling. A companion paper addresses the case of jet breakout, where diverging magnetic flux surfaces yield strong MHD acceleration over a wider range of Lorentz factor.},
doi = {10.1088/0004-637X/767/2/142},
url = {https://www.osti.gov/biblio/22126901}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 767,
place = {United States},
year = {Sat Apr 20 00:00:00 EDT 2013},
month = {Sat Apr 20 00:00:00 EDT 2013}
}