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Published June 26, 1997 | public
Journal Article

Spectral constraints on the redshift of the optical counterpart to the γ-ray burst of 8 May 1997

Abstract

Brief, intense bursts of y-rays occur approximately daily from random directions in space, but their origin has remained unknown since their initial detection almost 25 years ago. Arguments based on their observed isotropy and apparent brightness distribution are not sufficient to constrain the location of the bursts to a local or cosmological origin. The recent detection of a counterpart to a y-ray burst at other wavelengths has therefore raised the hope that the sources of these energetic events might soon be revealed. Here we report spectroscopic observations of the possible optical counterpart to the y-ray burst GRB970508. The spectrum is mostly featureless, except for a few prominent absorption lines which we attribute to the presence of an absorption system along the line of sight at redshift z = 0.835. Coupled with the absence of Lyman-α forest features in the spectra, our results imply that the optical transient lies at 0.835 ≾ z ≾ 2.3. If the optical transient is indeed the counterpart of GRB970508, our results provide the first direct limits on the distance to a y-ray burst, confirming that at least some of these events lie at cosmological distances, and are thus highly energetic.

Additional Information

© 1997 Macmillan Publishers Ltd. Received 21 May; accepted 3 June 1997. We thank the BeppoSAX team for their efforts in disseminating information to observers for rapid identification of an optical transient, making this work possible. We thank W. Sargent and M. Pahre for discussions, and the Keck Observatory staff for assistance at the telescope. This work is based on observations obtained at the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology and the University of California. M.R.M. was supported by Caltech; S.R.K. was supported by NASA and NSF; S.G.D. was supported by NSF and the Bressler Foundation; C.C.S. was supported by NSF and the Sloan Foundation.

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023