Looking at the Black Hole That Powers Long Gamma Ray Bursts

Antonios Nathanail, ITP, Goethe Universität, Frankfurt

Gamma-ray bursts (GRBs) are violent explosions, coming from cosmological distances. They are detected in gamma-rays (also X-rays, UV, optical, radio) almost every day, and have typical durations of a few seconds to a few minutes. Some GRBs have been reported with extraordinary duration of 10⁴ sec. These are called Ultra Long GRBs. We review some observational features of GRBs.According to Blandford & Znajek (1977), the spin energy of a rotating black hole can be extracted electromagnetically, should the hole be endowed with a magnetic field supported by electric currents in a surrounding disk. We argue that this can be the case for the central engines of GRBs and we show that the lightcurves of several Long GRBs are following closely the theoretical curve of Black Hole Spin Down, thus their duration is completely characterised by the magnetic flux accumulated at the event horizon of the black hole. We further discuss how X-ray flares are produced in Long GRBs.