Crab GeV flares from corrugated termination shock

TL;DR

This paper investigates how low frequency magnetosonic waves cause shock corrugation in the Crab nebula, leading to short gamma-ray flares through Doppler-boosted synchrotron emission, combining analytical and numerical methods.

Contribution

It provides a novel analytical and numerical study of shock corrugation effects on gamma-ray flares in the Crab nebula, linking wave interactions to observable phenomena.

Findings

Shock corrugation induces time-dependent post-shock flows.

Mild Doppler boosting explains short gamma-ray flares.

Simulations match observed flare durations.

Abstract

Very high energy gamma-ray flares from the Crab nebular detected by AGILE and Fermi satellites challenge our understanding of the pulsar wind nebulae. The short duration of the flares, only few days, is particularly puzzling since it is much shorter than the dynamical times scale of the nebular. In this work we investigate analytically and via numerical simulations the electromagnetic signatures expected from the large amplitude low frequency magnetosonic waves generated within the Crab nebular which induce the corrugation perturbations of the termination shock. As a result, the oblique termination shock produces time-dependent, mildly relativistic post-shock flow. Using the relativistic MHD version of the RIEMANN code, we simulate the interaction of the termination shock with downstream perturbations. We demonstrate that mild Doppler boosting of the synchrotron emission in the post-shock flow can produce bright, short time scale flares.