Spectral evolution of long Gamma Ray Burst prompt emission: electrostatic acceleration and adiabatic expansion

TL;DR

This paper proposes a model combining electrostatic acceleration and adiabatic expansion to explain the spectral evolution of long Gamma Ray Burst prompt emissions, aligning well with observed spectral decay patterns.

Contribution

It introduces a novel scenario integrating electrostatic acceleration and adiabatic expansion to interpret GRB spectral evolution, especially during pulse decay phases.

Findings

Spectral evolution matches observed hardness-intensity correlation.

Adiabatic expansion dominates energy losses during pulse decay.

Model explains the peak energy distribution at ~0.25 MeV.

Abstract

Despite the great variation in the light curves of Gamma Ray Burst (GRB) prompt emission, their spectral energy distribution is generally curved and broadly peaked. In particular, their spectral evolution is well described by the hardness-intensity correlation during a single pulse decay phase, when the SED peak height S_p decreases as its peak energy E_p decreases. We propose an acceleration scenario, based on electrostatic acceleration, to interpret the E_p distribution peak at ~ 0.25 MeV. We show that during the decay phase of individual pulses in the long GRB light curve, the adiabatic expansion losses likely dominate the synchrotron cooling effects. The energy loss as due to adiabatic expansion can also be used to describe the spectral evolution observed during their decay phase. The spectral evolution predicted by our scenario is consistent with that observed in single pulses of long BATSE GRBs.