AAS 198th Meeting, June 2001
Session 35. GRBs: A Mystery and a Tool
Topical Session Oral, Tuesday, June 5, 2001, 8:30am-12:30pm, 2:00-5:30pm, C107

## [35.08] GRBs from Collapsars

A collapsar is a massive rotating star (M\rm ms \gtrsim 25 M\odot) whose core collapses to form a black hole. In a rapidly rotating star, the accretion of the rest of the star into the newly-formed black hole produces an energetic long-duration gamma-ray burst (GRB) accompanied by a Type Ib/c supernova. An accretion disk forms as the outer layers of the star fall into the black hole (3 \lesssim {\rm Mhole}/M\odot \lesssim 10) at its center. Rapid accretion of stellar matter into the hole at rates of up to 0.1\, M\odot\,{\rm s}-1 releases large amounts of energy (\approx 1051 erg s-1) some of which is deposited in the low density rotation axis of the star. The heated gas at the pole expands in a jet-like fireball which penetrates the surface of the star, escapes to large distances, and makes the observed gamma-ray photons and lower energy afterglow at large distances (> 1000 stellar radii). Since collapsars naturally form jetted explosions beamed to approximately 1% of the sky, the energetic requirement is typically hundreds of times less than the observed isotropic equivalent energy.'' Supernova-like energies of 1051-1052 ergs, as calculated in detailed models to be presented, are therefore sufficient to explain GRBs with a range of isotropic equivalent energies up to, and exceeding, 1054 ergs depending on the beaming angle.