Adiabatic non-resonant acceleration in magnetic turbulence and hard spectra of gamma-ray bursts

Abstract

We introduce a non-resonant acceleration mechanism arising from the second adiabatic invariant in magnetic turbulence and apply it to study the prompt emission spectra of gamma-ray bursts (GRBs). The mechanism contains both the first- and second-order Fermi acceleration, originating from the interacting turbulent reconnection and dynamo processes. It leads to a hard electron energy distribution up to a cutoff energy at the balance between the acceleration and synchrotron cooling. The sufficient acceleration rate ensures a rapid hardening of any initial energy distribution to a power-law distribution with the index $p\sim 1$, which naturally produces a low-energy photon index $\alpha \sim -1$ via the synchrotron radiation. For typical GRB parameters, the synchrotron emission can extend to a characteristic photon energy on the order of $\sim 100$ keV.

5 pages, 2 figures; accepted for publication in ApJL

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• Magnetic field amplification in supernova remnants
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• Non-resonant particle acceleration in strong turbulence: comparison to kinetic and MHD simulations
• Powerlaw spectra from stochastic acceleration
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• Particle Energy Diffusion in Linear Magnetohydrodynamic Waves
• Nonlinear aspects of stochastic particle acceleration
• On the broad-band synchrotron spectra of pulsar wind nebulae
• A sudden dramatic change and recovery of magneto-environment of a repeating fast radio burst
• Magnetic reconnection-driven turbulence and turbulent reconnection acceleration
• Statistical properties of Fermi GBM GRBs' spectra
• Acceleration of cosmic rays in presence of magnetohydrodynamic fluctuations at small scales
• Synchrotron spectra of GRB prompt emission and pulsar wind nebulae