Spectroscopic Limits on the Distance and Energy Release of GRB 990123

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Science  26 Mar 1999:
Vol. 283, Issue 5410, pp. 2075-2077
DOI: 10.1126/science.283.5410.2075

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An optical spectrum of the afterglow from the unusually bright gamma-ray burst GRB 990123 obtained on 24.25 January 1999 universal time showed an absorption system at a redshift ofz = 1.600. The absence of a hydrogen Lyman α forest sets an upper limit of z < 2.17, whereas ultraviolet photometry indicates an upper limit of z < 2.05. The probability of intersecting an absorption system as strong as the one observed along a random line of sight out to this z is at most a few percent, implying that GRB 990123 was probably atz = 1.600. Currently favored cosmological parameters imply that an isotropic energy release equivalent to the rest mass of 1.8 neutron stars (4.5 × 1054 erg) was emitted in gamma rays. Nonisotropic emission, such as intrinsic beaming, may resolve this energy problem.

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