Prof. David N. Burrows: GRB Jet Breaks and Energetics in the Swift/Chandra era
Source: Monday physics colloquium
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GRB Jet Breaks and Energetics in the Swift/Chandra era
Prof. David N. Burrows*, Department of Astronomy and Astrophysics, Penn State University, State College, PA, USA
Gamma-Ray Bursts emit tremendous amounts of energy on timescales ranging from less than a second to hundreds of seconds. We have strong evidence that they must be highly beamed, which means that our knowledge of their true energetics relies on understanding the beaming angles of the relativistic jets. The jet opening angles can in principle be measured through the characteristic "jet break" in the GRB light curves. Work a decade ago suggested that these jet breaks occur on typical timescales of a few days. The Swift satellite, which produces detailed, relatively uniform light curves for GRBs that often extend to a few weeks after the explosion, was expected to measure jet breaks on a regular basis, providing good determinations of jet opening angles. To our surprise, this has not been the case. Swift has found much more complex light curves than anticipated on the basis of earlier data, but cases of clear jet breaks are present in only a few percent of the more than 730 GRBs observed to date by Swift. Theoretical work over the past several years has suggested various explanations for the lack of clear jet break signatures in the Swift X-ray light curves.
Recent GRB jet models are now providing a good framework for fitting light curves to detailed hydro/radiation codes that may allow us to finally begin measuring the jet properties for a large class of GRBs. We have begun to apply these models to data sets that feature good X-ray light curves from Swift XRT and Chandra ACIS observations, and I will discuss preliminary results from that work.