The "Crab Phenomenon": the Mysterious Gamma-Ray Flares of the Crab Nebula
Abstract
The Crab Nebula, the "Queen of Nebulae", is full of surprises. The inner Nebula is an exceptional accelerator capable of energizing electrons/positrons up to PeV energies. Until recently, ideal MHD-based models of the Nebula and of its accelerating sites appeared to be satisfactory in explaining the Crab average properties. Week-month variability of local "spots" of the inner Nebula detected in optical and X-rays was attributed to local instabilities of relativistic outflow. However, the overall X-ray/gamma-ray Nebular flux appeared to be essentially stable. This paradigm was dramatically shattered by the 2010 discovery by AGILE and the Fermi-LAT confirmation of transient gamma-ray emission from the Crab. Six major gamma-ray flares attributed to the Crab Nebula have been detected since 2008. A novel mechanism of particle acceleration is acting on very short timescales (hours), and is incompatible with ideal MHD models. Plasma instabilities and magnetic field reconnection producing runaway acceleration can be invoked, but the acceleration site and detailed mechanism are controversial. This "Crab phenomenon" has profound theoretical and observational impacts. We will discuss the current theoretical modeling of the Crab gamma-ray flares and the implications for relativistic jets and laboratory plasmas. In particular, we will review recent progress in 3D modelling of the "South-East jet" and of its instabilities that are candidate sites of flaring emission.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E3310T