Gamma-ray burst spectrum with decaying magnetic field

Xiaohong Zhao, Zhuo Li, Xuewen Liu, Bin Bin Zhang, Jinming Bai, Peter Mészáros

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

In the internal shock model for gamma-ray bursts (GRBs), the synchrotron spectrum from the fast cooling electrons in a homogeneous downstream magnetic field (MF) is too soft to produce the low-energy slope of GRB spectra. However, the MF may decay downstream with distance from the shock front. Here we show that the synchrotron spectrum becomes harder if electrons undergo synchrotron and inverse-Compton cooling in a decaying MF. To reconcile this with the typical GRB spectrum with low-energy slope νF ν∝ν, the postshock MF decay time must be comparable to the cooling time of the bulk electrons (corresponding to a MF decaying length typically of ∼10 5 skin depths); that the inverse-Compton cooling should dominate synchrotron cooling after the MF decay time; and/or that the MF decays with comoving time roughly as B∝t -1.5. An internal shock synchrotron model with a decaying MF can account for the majority of GRBs with low-energy slopes not harder than ν4/3.

Original languageEnglish (US)
Article number12
JournalAstrophysical Journal
Volume780
Issue number1
DOIs
StatePublished - Jan 1 2014

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gamma ray bursts
magnetic field
synchrotrons
magnetic fields
cooling
decay
slopes
electron
shock
energy
electrons
shock fronts
skin

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Zhao, X., Li, Z., Liu, X., Zhang, B. B., Bai, J., & Mészáros, P. (2014). Gamma-ray burst spectrum with decaying magnetic field. Astrophysical Journal, 780(1), [12]. https://doi.org/10.1088/0004-637X/780/1/12
Zhao, Xiaohong ; Li, Zhuo ; Liu, Xuewen ; Zhang, Bin Bin ; Bai, Jinming ; Mészáros, Peter. / Gamma-ray burst spectrum with decaying magnetic field. In: Astrophysical Journal. 2014 ; Vol. 780, No. 1.
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Zhao, X, Li, Z, Liu, X, Zhang, BB, Bai, J & Mészáros, P 2014, 'Gamma-ray burst spectrum with decaying magnetic field', Astrophysical Journal, vol. 780, no. 1, 12. https://doi.org/10.1088/0004-637X/780/1/12

Gamma-ray burst spectrum with decaying magnetic field. / Zhao, Xiaohong; Li, Zhuo; Liu, Xuewen; Zhang, Bin Bin; Bai, Jinming; Mészáros, Peter.

In: Astrophysical Journal, Vol. 780, No. 1, 12, 01.01.2014.

Research output: Contribution to journalArticle

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Zhao X, Li Z, Liu X, Zhang BB, Bai J, Mészáros P. Gamma-ray burst spectrum with decaying magnetic field. Astrophysical Journal. 2014 Jan 1;780(1). 12. https://doi.org/10.1088/0004-637X/780/1/12