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Abstract: Studies of GRB host galaxies are crucial to understanding GRBs. However,since they are identified by the superposition in the plane of the sky of a GRBafterglow and a galaxy there is always a possibility that an associationrepresents a chance alignment, rather than a physical connection. We examine auniform sample of 72 GRB fields to explore the probability of chancesuperpositions. There is typically a ~1% chance that an optical afterglow willcoincide with a galaxy by chance. While spurious host galaxy detections will,therefore, be rare, the possibility must be considered when examiningindividual GRB-host galaxy examples. It is also tempting to use the large anduniform collection of X-ray afterglow positions to search for GRB-associatedgalaxies. However, we find that approximately half of the 14 superpositions inour sample are likely to occur by chance, so in the case of GRBs localized onlyby an X-ray afterglow, even statistical studies are suspect.

Author: Bethany E. Cobb, Charles D. Bailyn


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