{
  "bibcode": "2002GCN..1611....1S",
  "body": "Isabel Salamanca(1), Evert Rol(1), Ralph Wijers (1), Sara Ellison(2),\nLex Kaper(1), and Nial Tanvir (3) (1) University of Amsterdam (2)\nUniversidad Catolica de Chile (3) University of Hertfordshire, report:\n\nWe obtained a spectrum with the double arm spectrograph ISIS at the\n4.2-m WHT telescope at La Palma (Spain) on October 4. A partial\ncalibration of the blue arm spectrum (2 Angstrom spectral resolution)\nreveals the presence of four absorption components at detected in CIV\nat redshifts 2.295, 2.298, 2.320, and 2.327, i.e. spanning a total\nvelocity range of approximately 3000 km/s.  The latter three\ncomponents are also clearly detected in SiIV, with a marginal\ndetection of SiIV at z=2.295.  The lines around 4000-4050 Angstrom can\nbe then identified as Ly-alpha (for which we also detect the emission\ncomponent reported earlier); there is a close match for the components\nat z=2.320 and 2.327, whilst the two lowest redshift Lya components\nare blended.\n\nThe interpretation of this 4-component absorption system could be of\nabsorption local to the burst source, or of cosmological components.\n\nIf all arise local to the burst, we must be viewing through ejecta in\na supernova-like explosion. After a day, supernova ejecta are so\nopaque that we cannot see through them, and so we must be viewing the\nresults of an explosion that occurred weeks or more before the burst,\nas in the supranova model. The narrowness of the components then must\nmean that the ejecta have already cooled and partly condensed into\nfilaments. It is a challenge to have this happen within weeks, and\ngiven the small filling factor inherent to filamentation, to have our\nline of sight intersect four filaments.\n\nIf cosmological, we see our line of sight pass through 4 mass\nconcentrations of a magnitude well in excess of lyman limit systems in\nquasar absorption line terms. These would all be local to the host\ngalaxy in cosmological terms, but with velocity separations large for\neven a present-day massive cluster. Given that only 10-20% of quasars\nat redshift 1 - 2 have even one such system, one concludes nonetheless\nthat seeing four systems implies a physical relation between them.\nThus we would be seeing a very large cosmic structure at z=2.3 with an\nextent of 3000 km/s in velocity space. This is very difficult to get\nin any cosmology, and would push cosmological models to very low\nvalues of Omega_matter.\n\nFurther high-resolution spectroscopy is required to resolve the\nvelocity structure, and to determine the abundances and thermodynamic\nstate of these absorption systems, in order that we may understand the\nnature of this remarkable system. In local models, one might find\nvariability in the Lyman-alpha emission.  Since the source is now\nfading past R=21, these observations are most urgent.\n\nThis message may be cited.",
  "circularId": 1611,
  "createdOn": 1034198048000,
  "email": "nrt@ast.cam.ac.uk",
  "subject": "GRB 021004: optical spectroscopy",
  "submitter": "Nial Tanvir at IofA U.Cambridge  <nrt@ast.cam.ac.uk>",
  "eventId": "GRB 021004"
}