{
  "bibcode": "2008GCN..8301....1V",
  "body": "Paul Vreeswijk, Daniele Malesani, Johan Fynbo (DARK/NBI), Pall\nJakobsson (U. of Iceland), Christina Thoene, Jesper Sollerman, Darach\nWatson, Bo Milvang-Jensen (DARK/NBI) report on behalf of a larger\ncollaboration:\n\nThe afterglow of GRB 080928 detected by Swift (Sakamoto et al., GCN\n8292, see also Rykoff et al., GCN 8293) was observed with FORS2\nmounted on the Antu telescope of ESO's VLT on Cerro Paranal, Chile.\nFollowing an acquisition image, which was started at 6:31 UT on\nSeptember 29, 2008 (15.5 hr after the GRB trigger), a single 1800 s\nspectrum was secured. It was taken with a 1\" slit and the 300V grism,\nresulting in an approximate resolution of 11 A, and a useful\nwavelength coverage of 3800-9300 A. From the 60 s acquisition image,\nwe measure an afterglow magnitude of R = 20.4 based on USNO-B1\nmagnitudes.\n\nThe extracted spectrum shows a multitude of significant absorption\nlines, which we identify with common resonance lines of mainly MgII\nand FeII, originating in at least two absorption systems at z=0.735\nand z=1.692. The latter redshift presumably corresponds to that of the\nGRB host galaxy. We do not find evidence for a spectral break due to\nthe Lyman alpha forest down to 3800 A, setting a firm upper limit on\nthe GRB redshift of z < 2.1. These results are consistent with the\nredshift limits set by GROND (Rossi et al., GCN 8296) and UVOT (Kuin\net al., GCN 8298), but not with the value of z=2.49 reported by\nCucchiara et al. (GCN 8300).\n\nThe equivalent width of the MgII 2796 line of the z=0.735 system\n(EW_rest ~ 4.3 A) is much larger than that of the z=1.692 system. We\nnote the presence of an R ~ 22 object, not covered by the slit, at\n2.6\" NNE of the afterglow position, which could possibly be a bright\nhost galaxy, or the counterpart of the z=0.735 absorber. The slit\nserendipitously covers a galaxy 30\" away from the afterglow (at\nR.A. 06:20:13.35, decl. -55:11:55.0), which shows an apparent emission\nline at 6470 A; this can be identified as [OII] 3727 at a redshift of\nz=0.736. At this redshift, 2.6 and 30\" correspond to projected\ndistances of 19 and 219 kpc, respectively.\n\nWe are grateful for the excellent support from the Paranal observing\nstaff, in particular Stephane Brillant, Michelle Doherty and Patricia\nGuajardo.",
  "circularId": 8301,
  "createdOn": 1222705589000,
  "email": "pmv@dark-cosmology.dk",
  "subject": "GRB 080928: VLT redshift",
  "submitter": "Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen  <pmv@dark-cosmology.dk>",
  "eventId": "GRB 080928"
}