The energetics and environments of Swift gamma-ray bursts
Abstract
For their short durations, γ-ray bursts (GRBs) are the most electromagnetically luminous objects in the universe. In this thesis, I use these fascinating objects, both as signposts, indicating the presence of an ultra-relativistic (Lorentz factor ? 102-103) outflow from a newly born stellar mass black hole, and as lighthouses, illuminating the circumburst (r ? 1 pc) and inter-stellar (r ? 1 kpc) media along the line of sight. In Part I, I describe my efforts to automate the Palomar 60 inch telescope (P60), the primary instrument on which much of this thesis is based. Designed to capitalize on NASA's recently launched Swift γ-Ray Burst Explorer, P60 now routinely provides moderately fast (t . 3min) and sustained (R . 23mag) observations of GRB afterglows and other optical transients. Part II focuses on the geometry and energetics of some of the best-sampled events in the Swift era. I find both GRB050820A and GRB060418 are an order of mag- nitude more energetic than pre-Swift events, with a total energy release in excess of 1052 erg. Both GRBs are therefore members of an emerging class of "hyper-energetic" events, suggesting a much broader energy distribution then previously thought and challenging current massive star progenitor models. Finally, in Part III I study the environments of long-duration GRBs. The massive star progenitors should leave an imprint on the GRB environment, both on the pc scale as a wind from mass loss of the outer envelope, and on the kpc scale from the dense, dusty disk where massive stars form. Interestingly, I demonstrate that GRB070125 exploded in a halo environment, suggesting at least some massive stars form far way from the disk of their host. By comparing the X-ray and optical light curves from a sample of 29 GRBs, I find nearly half show evidence for suppressed optical emission. I attribute this to dust absorption in the host galaxy, consistent with a massive star origin for long-duration GRBs.
- Publication:
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Ph.D. Thesis
- Pub Date:
- November 2009
- Bibcode:
- 2009PhDT.......322C