Probing Dust with Gamma-Ray Bursts

Long-duration gamma-ray bursts (GRBs) result from the deaths of certain massive stars Since GRBs occur in actively starforming regions, there should be significant dust extinction of their optical afterglows The dust properties of GRB environments are of interest not only for their value in studies of GRB and their formation, but also because GRBs occur in starforming galaxies at very high redshifts (currently < z > = 2 2), and GRB afterglows give us a means to study dust and metallicity in the hearts of extremely distant starforming regions that are accessible in no other way Their brightness and simple, power-law spectra across a wide wavelength range, makes them well-suited to extinction studies in star-forming regions at all redshifts The vast majority of reddening curves have been featureless-the 2175 angstrom bump for example has only been detected in a GRB host galaxy for the first time very recently and is presented here Another new, unusual extinction curve is also briefly presented Extinctions derived solely from the reddening in GRB optical/near IR spectra have so far been relatively low and at the same time those reddening measurements disagree strongly with extinctions inferred from metallicity measurements and have led to the suggestion of a flat dust extinction curve (grey dust), possibly because of dust destruction by the GRB In spite of the large literature on grey dust and the alteration of the extinction curve by dust destruction, its existence has so far never been demonstrated because of the difficulty in obtaining absolute extinction curves