{
  "bibcode": "2002GCN..1605....1C",
  "body": "R. Chornock and A. V. Filippenko, University of California, Berkeley,\nreport that optical spectra (range 300-940 nm) of the GRB 021004\nafterglow (GCN 1564, 1565) were obtained with the Low Resolution\nImaging Spectrometer on the Keck-I 10-m telescope on Oct. 8 UT.  We\ndetect the absorption lines due to Mg I, Mg II, and Fe II associated\nwith systems at z=1.381 and 1.603 previously noted (GCN 1569).  We\nalso detect the unidentified absorption lines at 463, 466, 510, and\n514.5 nm reported in GCN 1579, as well as the narrow emission line at\n405 nm and the absorption lines between 400 and 404 nm (GCN 1599).\n\nWe identify the emission line as Lyman-alpha at z=2.323, in\ncontradiction to the identification as C IV in GCN 1599.  We note that\nP-Cygni absorption line profiles from a hypothetical starburst host\ngalaxy should not be prominent above the bright continuum of the\ntransient.  In addition, we feel that a lone UV emission line is\nsignificantly more likely to be Lyman-alpha than C IV.  The\npreviously unidentified absorption lines can now be identified as the\nSi IV 1393.8, 1402.8 Angstrom doublet and C IV 1548.2, 1550.8\nAngstrom doublet.  These absorption lines have multiple velocity\ncomponents, as does the Lyman-alpha absorption.  We note the\nwavelength coincidence of one of the components of Lyman-alpha with\nthe expected C IV absorption from the Mg II system at z=1.603, but\nbelieve it only to be a coincidence.\n\nAn additional point in favor of the z=2.323 interpretation is the\nappearance of the continuum to the blue of the Lyman-alpha line.\nWhile there is no substantial Lyman break, there are many more\nabsorption lines blueward of Lyman-alpha than redward.  A previously\nunnoted absorption feature with multiple components is present at\n341 nm, consistent with Lyman-beta at this redshift.\n\nThis message may be cited.",
  "circularId": 1605,
  "createdOn": 1034095786000,
  "email": "alex@astro.berkeley.edu",
  "subject": "GRB 021004 redshift",
  "submitter": "Alex Filippenko at UC Berkeley  <alex@astro.berkeley.edu>",
  "eventId": "GRB 021004"
}