Inductive Spikes in the Crab Nebula: A Theory of γ-Ray Flares.

John G Kirk,Gwenael Giacinti

doi:10.1103/physrevlett.119.211101

Abstract

We show that the mysterious, rapidly variable emission at ∼400 MeV observed from the Crab Nebula by the AGILE and Fermi satellites could be the result of a sudden drop in the mass loading of the pulsar wind. The current required to maintain wave activity in the wind is then carried by very few particles of a high Lorentz factor. On impacting the nebula, these particles produce a tightly beamed, high-luminosity burst of hard gamma rays, similar to those observed. This implies that (i)the emission is synchrotron radiation in the toroidal field of the nebula and, therefore, linearly polarized and (ii)this mechanism potentially contributes to the gamma-ray emission from other powerful pulsars, such as the Magellanic Cloud objects J0537-6910 and B0540-69.

Highlights

We show that the mysterious, rapidly variable emission at ∼400 MeV observed from the Crab Nebula by the AGILE and Fermi satellites could be the result of a sudden drop in the mass loading of the pulsar wind
The detection of powerful gamma-ray flares from the Crab Nebula by the AGILE satellite and the Large Area Telescope on the Fermi satellite [1,2,3] has provided theorists with three major puzzles: How are particles able to emit synchrotron radiation well above the ∼100 MeV astrophysical “upper limit” [4]? What is the geometry and location of the source, given that it varies on a time scale of hours, whereas the nebula has a light-crossing time of months? By which mechanism can such a small source achieve a power only one order of magnitude less than that of the entire nebula? Many theories have addressed these issues, but none has yet achieved general acceptance
The new theory predicts the polarization properties of the flares, which may be measurable in the near future [8], and suggests that a similar emission may be detectable from other pulsar wind nebulae

Summary

Introduction

We show that the mysterious, rapidly variable emission at ∼400 MeV observed from the Crab Nebula by the AGILE and Fermi satellites could be the result of a sudden drop in the mass loading of the pulsar wind. We present a solution to this problem: Assuming that the pulsar wind is launched as a mildly supersonic magnetohydrodynamic (MHD) flow with embedded magnetic fluctuations, we demonstrate that inductive acceleration converts 10% of the power into kinetic energy.

Results

Conclusion