title: Observation of X-ray lines from a gamma-ray burst (GRB991216): evidence of moving ejecta from the progenitor.
abstract: We report on the discovery of two emission features observed in the x-ray spectrum of the afterglow of the gamma-ray burst (GRB) of 16 December 1999 by the Chandra X-ray Observatory. These features are identified with the Ly(alpha) line and the narrow recombination continuum by hydrogenic ions of iron at a redshift z = 1.00 +/- 0.02, providing an unambiguous measurement of the distance of a GRB. Line width and intensity imply that the progenitor of the GRB was a massive star system that ejected, before the GRB event, a quantity of iron approximately 0.01 of the mass of the sun at a velocity approximately 0.1 of the speed of light, probably by a supernova explosion.
authors.affiliation: Istituto Astrofisica Spaziale, Consiglio Nazionale delle Ricerche (CNR), Via Fosso del Cavaliere, 00133 Roma, Italy. piro@ias.rm.cnr.it
authors.forename: L
authors.initials: L
authors.lastname: Piro
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authors.lastname: Garmire
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authors.lastname: Garcia
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authors.lastname: Stratta
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authors.lastname: Feroci
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authors.lastname: Mészáros
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authors.lastname: Vietri
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authors.lastname: Bradt
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authors.lastname: Halpern
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authors.lastname: Heise
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authors.lastname: Hurley
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authors.lastname: Kawai
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authors.lastname: Kippen
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authors.lastname: Marshall
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authors.lastname: Murakami
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authors.lastname: Sokolov
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authors.lastname: Takeshima
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authors.lastname: Yoshida