%0 Generic %1 Rapoport2011 %A Rapoport, Sharon %A Onken, Christopher A. %A Schmidt, Brian P. %A Wyithe, J. Stuart B. %A Tucker, Brad E. %A Levan, Andrew J. %D 2011 %K GRB MgII excess lensing %T Testing the gravitational lensing explanation for the MgII problem in GRBs %U http://arxiv.org/abs/1108.5235 %X Sixty percent of gamma-ray bursts (GRBs) reveal strong MgII absorbing systems, which is a factor of ~2 times the rate seen along lines-of-sight to quasars. The discrepancy in the covering factor is most likely to be the result of either quasars being obscured due to dust, or the consequence of many GRBs being strongly gravitationally lensed. We analyze observations of GRBs that show strong foreground MgII absorption. We Monte-Carlo the distances between foreground galaxies in the HUDF and lines of sight distributed randomly within a radius derived from the covering factor, and find that galaxies are located systematically closer to the position of the observed GRBs than expected for random lines of sight. This over-density at small impact parameters is statistically more robust than the well known excess of MgII absorbers among GRB afterglow spectra, and presents a new puzzle for MgII absorption studies. The over-density cannot be explained by obscuration in the GRB sample, but is a natural consequence of gravitational lensing. Upon examining the particular configurations of galaxies near a sample of GRBs with strong MgII absorption, we find several intriguing lensing candidates. We suggest that lensing is a viable explanation of the MgII enhancement in GRBs, and outline the future observations required to test this hypothesis conclusively.

@misc{Rapoport2011, abstract = { Sixty percent of gamma-ray bursts (GRBs) reveal strong MgII absorbing systems, which is a factor of ~2 times the rate seen along lines-of-sight to quasars. The discrepancy in the covering factor is most likely to be the result of either quasars being obscured due to dust, or the consequence of many GRBs being strongly gravitationally lensed. We analyze observations of GRBs that show strong foreground MgII absorption. We Monte-Carlo the distances between foreground galaxies in the HUDF and lines of sight distributed randomly within a radius derived from the covering factor, and find that galaxies are located systematically closer to the position of the observed GRBs than expected for random lines of sight. This over-density at small impact parameters is statistically more robust than the well known excess of MgII absorbers among GRB afterglow spectra, and presents a new puzzle for MgII absorption studies. The over-density cannot be explained by obscuration in the GRB sample, but is a natural consequence of gravitational lensing. Upon examining the particular configurations of galaxies near a sample of GRBs with strong MgII absorption, we find several intriguing lensing candidates. We suggest that lensing is a viable explanation of the MgII enhancement in GRBs, and outline the future observations required to test this hypothesis conclusively. }, added-at = {2011-08-29T17:18:36.000+0200}, author = {Rapoport, Sharon and Onken, Christopher A. and Schmidt, Brian P. and Wyithe, J. Stuart B. and Tucker, Brad E. and Levan, Andrew J.}, biburl = {https://www.bibsonomy.org/bibtex/2e139c1a306b5af94adf432857f1b4685/miki}, description = {[1108.5235] Testing the gravitational lensing explanation for the MgII problem in GRBs}, interhash = {44cb31a2874dafdc4178af1e50a1d987}, intrahash = {e139c1a306b5af94adf432857f1b4685}, keywords = {GRB MgII excess lensing}, note = {cite arxiv:1108.5235}, timestamp = {2011-08-29T17:18:36.000+0200}, title = {Testing the gravitational lensing explanation for the MgII problem in GRBs}, url = {http://arxiv.org/abs/1108.5235}, year = 2011 }