Dark bursts in the Swift Era

We present multi-color optical observations of long-duration GRBs made over a three year period with the robotic Palomar 60 inch telescope (P60). We argue that previous studies, by selecting only the brightest and best-sampled optical afterglows, have significantly underestimated the amount of dust present in typical GRB environments.

Dark bursts and multivariate statistics A significant  fraction of GRBs does not show detectable OT fluences. Performing a Kaplan-Meier product limit estimation we obtained an  unbiased cumulative distribution of the V visual brightness. Using the discriminant analysis of the multivariate statistical analysis we compare the distribution of the physical quantities of the optically dark and bright GRBs, detected by the BAT and XRT.

Collimation and energetics of  Swift GRBs

We present multi-wavelength (radio through X-ray) observations of GRBs 050820A, 060418, and 080319B, and construct afterglow models to extract the opening angle and beaming-corrected energy release for all three events. We find evidence for an achromatic jet break in all five events, strongly supporting the canonical picture of GRBs.

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