Crab Nebula Gamma-ray Flares as Relativistic Reconnection Events

Multiple gamma-ray flares have been discovered by FERMI and AGILE in the last year from the Crab Nebula, a source previously thought to be a standard candle. The short flare time scales (weeks to hours), luminosity, and typical photon energy provide interesting constraints on the emission region properties that suggest it has a Doppler factor of at least a few. We propose the flare intermittency and bulk relativistic motion are well explained by spontaneous reconnection events leading to relativistic outflows that occur in a turbulent highly magnetized (sigma > few) region of the nebula. We model the high energy nebula as the superposition of emission from many reconnection events and make statistical predictions about the gamma-ray variability. In this model, most of the outflows are directed away from Earth and are the source of the steady emission, while flares occur in the rare event that a reconnection outflow is directed at Earth. The probability density of flare flux goes as 1/F, implying that the average flux is dominated by rare bright events as expected from observations.