On the synchrotron spectrum of GRB prompt emission

Abstract

The prompt emission spectrum of Gamma-ray bursts (GRB) is characterized by a smoothly joint broken power-law spectrum known as the Band function. The typical low-energy photon index is $\sim -1$, which poses challenge to the standard synchrotron radiation models. We investigate the electron energy spectrum as a result of the interplay among adiabatic stochastic acceleration (ASA), particle injection, and synchrotron cooling. In the ASA-dominated low-energy range, ASA enables an efficient hardening of the injected energy spectrum to approach a spectral index $-1$. In the synchrotron cooling-dominated high-energy range, the injected high-energy electrons undergo fast synchrotron cooling and have a softer photon spectrum. With the energy range of the injected electrons broadly covering both the ASA- and synchrotron cooling-dominated ranges, the resulting photon number spectrum has the low- and high-energy indices as ${\alpha }_s\sim -1$ and ${\beta }_s\sim -p/2-1$, respectively. The break energy is of the order of $\sim 100$ keV, depending on the turbulence properties.

9 pages, 3 figures, accepted for publication in ApJ

References in corpus (7)

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• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
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• Relativistic MHD simulations of collision-induced magnetic dissipation in Poynting-flux-dominated jets/outflows
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• Trapping of cosmic rays in MHD turbulence
• Gamma-ray Bursts Induced by Turbulent Reconnection
• Pitch-Angle Anisotropy Imprinted by Relativistic Magnetic Reconnection
• On the broad-band synchrotron spectra of pulsar wind nebulae
• Synchrotron-Self-Compton radiation from magnetically-dominated turbulent plasmas in relativistic jets
• Electromagnetic Counterparts of Compact Binary Mergers
• Synchrotron radiation from electrons with a pitch-angle distribution
• The Low-Energy Spectral Index of Gamma-Ray Burst Prompt Emission from Internal Shocks
• Synchrotron spectra of GRB prompt emission and pulsar wind nebulae