Fast-cooling synchrotron radiation in a decaying magnetic field and γ-ray burst emission mechanism

Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that s...

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Bibliographic Details
Published inNature physics Vol. 10; no. 5; pp. 351 - 356
Main Authors Uhm, Z. Lucas, Zhang, Bing
Format Journal Article
LanguageEnglish
Published 01.05.2014
Subjects
Cooling
Emission
Magnetic fields
Photons
Spectra
Spectral emissivity
Synchrotron radiation
Synchrotrons
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Summary:Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that such 'fast cooling' electrons have a power-law distribution in energy with an index -2, and their synchrotron radiation has a photon spectral index-1.5. On the other hand, in a transient expanding astrophysical source, such as a gamma -ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast-cooling electrons can have a harder energy spectrum. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon spectral index has a typical value-1 could be due to synchrotron radiation in this moderately fast-cooling regime.
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ISSN:1745-2473
1745-2481
DOI:10.1038/nphys2932