Christopher C. Lindner - Collapsars and GRBs

 

Collapsar Accretion and the Gamma Ray Burst Light Curve

Gamma ray bursts (GRBs) are among the most energetic events in the universe.  They are so energetic that in ten seconds they can give off as much energy in light as our sun will give off in its entire ten billion year lifetime.  They are bright enough to be seen across the universe.  Gamma Ray Bursts originate from explosions of energy that occured billions of years ago.  In fact, the oldest object ever to be observed was a recently discovered gamma ray burst which went off almost 13 billion years ago.

Gamma ray bursts seem to divide themselves in two overlapping categories: short and long GRB.  The short bursts are likely caused by the merging of two compact objects, such as a black hole and a neutron star.  My work focuses on long GRB.  Long gamma ray bursts vary in brightness on short timescales, starting with a bright, burst phase, followed by a quick decay in brightness, followed by a more constant plateau phase.

It is difficult to come up with a model that could explain such variation.  There is much evidence suggesting that these events may be related to "collapsars."  A collapsar is the death of a very large star - the core of which is so dense that it actually collapses into a black hole or neutron star, which consumes the remaining portion of the star from the inside out.  It is beleived that this process could create relativistic jets, which burst through the star, and provide the emissions we observe.

My work focuses on simulating these collapsars.  Because the brightness of the jets in the collapsar model would depend on how quickly matter falls into the central black hole, we predict that the accretion history of a collapsar should mimic the light curve of a gamma ray burst.

Our first results have been published in the Astrophysical Journal, and are available on astro-ph.  Our two dimensional hydrodynamic simulations show that collapsars have three distinct phases of accretion which are anagous to the phases observed in the GRB light curve.

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