Gamma-ray flares in the Crab Nebula : Magnetic reconnection at work ?

Séminaire IPAG de Benoît Cerutti (University of Colorado), jeudi 20 septembre 2012 à 11h00, IPAG seminar room

The unexpected detection of bright short-lived gamma-ray flares in the Crab Nebula in 2010, has attracted considerable interests among observers and theorists. This discovery implies that electrons and positrons are accelerated to PeV (10^15 eV) energies in a milliGauss magnetic field, challenging the most established models of particle acceleration and pulsar wind nebulae. In this talk, I will argue that the flares could be powered by the rapid dissipation of magnetic energy via magnetic reconnection in the nebula. Using Particle-In-Cell simulations, I will show that relativistic reconnection accelerates and focuses particles into a narrow beam wiggling in the plane of the reconnection layer. The expected high-energy synchrotron emission is highly beamed, and exhibits ultra-rapid time variability. This scenario provides a viable explanation for the flares in the Crab Nebula. This study suggests that reconnection could be at the origin of other astrophysical flares, such as e.g., TeV gamma-ray flares in blazars. I will discuss a few examples.