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Proposal ID = 12502
Principle Investigator =  Andrew Fruchter  - Space Telescope Science
Title = "From the Locations to the Origins of Short Gamma-Ray Bursts"
Time = Apr 14, 2012 18:01:17	- 22:16:12
Target =  GRB-080905A-HSTPOS
Instrument = WFC3/IR, WFC3/UVIS


Gamma Ray Bursts (GRBs) continue to be one of the most enigmatic phenomena in astronomy, coming in a wide variety of different types and being found in very different environments. One thing is clear; they are the most luminous events known in the universe since the Big Bang. The favored formation mechanism for long-duration GRBs is the collapse of a massive star, while for the short duration GRBs (durations < 1 second) it is the collision between two compact stars (i.e., neutron stars) that are in a binary star system. However, the details are far from certain in both cases. The locations of the GRBs relative to the light of the host galaxies represent an important clue to their origin, but the samples are so small that the results are not conclusive. This proposal aims to double the sample of short duration GRBs. Many GRBs are found in the outskirts of the host galaxies, and in some case, there is no galaxy nearby at all. This might imply that the GRB system has been ejected from the galaxy at high speed, but it may also simply be that the host galaxy is so faint that it has not been identified. The Hubble observations will check both possibilities.

Paraphrasing from the abstract:

While long-duration gamma-ray bursts (LGRBs) result from the collapse of massive stars, the progenitors of short-duration gamma-ray bursts (SGRBs) are still unknown. Although SGRBs are widely thought to result from the in-spiral of compact binaries, this is a conjecture. SGRBs have been found in elliptical galaxies, Abell clusters of galaxies, star-forming dwarfs and spirals. Analysis of our Cycle 16 and Cycle 17 programs shows that the vast majority of SGRBs are more widely distributed than the rest-frame UV light (lambda < 400nm) of their hosts, and may even be more widely distributed than the red light (lambda > 600 nm). These results may be an indication that the progenitors of SGRBs have significant velocities. We will use two lines of attack to obtain substantial new insight into the origins of SGRBs. 1) WFC3 IR imaging of eleven hosts will nearly double the number of hosts with HST imaging in the rest-frame red. If some of these bursts continue to show no evidence of an underlying host, models which predict neutron-star binaries with large velocities would be favored. 2) If an SGRB goes off in a nearby elliptical we will trigger a target of opportunity. The discovery of a globular cluster at the site of the explosion would provide revolutionary evidence that SGRBs are formed from compact binaries.

You can find most of this information and more from the following webpage: by entering "12502" in the Prop. ID box.