{
  "bibcode": "2002GCN..1259....1P",
  "body": "P.A. Price, B.P. Schmidt (RSAA, ANU) and S.R. Kulkarni (Caltech)\nreport on behalf of the larger REACT GRB collaboration:\n\nAs a part of our AO-9 HST GRB program, we observed the afterglow\n(Price et al GCN #1107) of GRB 010921 (Ricker et al. GCN #1096).\nWe obtained WFPC2 observations through multiple filters, designed\nto detect or constrain underlying supernovae for low-redshift\nGRBs.  The observations were obtained on 2001 Oct 26, Nov 6,\nNov 25 and 2002 Jan 4.  We have drizzled, registered and subtracted\nthe images to obtain host-subtracted fluxes at each of the first\nthree epochs, assuming the flux of the GRB in the final epoch\nimage is negligible.  The light-curve is available from\n\n            http://www.mso.anu.edu.au/~pap/grb010921/\n\nWe identify a break in the light-curve at approximately 35 days\nwhich may be due to collimation of the ejecta.  If so, then\nwe calculate a jet-corrected gamma-ray energy release of\n6.7 x 10^50 erg, consistent with the clustering of gamma-ray\nenergy releases found by Frail et al. (2001, ApJ, 562, L55).\n\nSN 1998bw at z = 0.451 should peak in the F702W and F814W bands,\nat approximately 4 uJy.  No evidence for such a component in the\nlight-curve is seen in the F555W, F702W, F814W and F850LP bands.\nThese measurements rule out the existence of a SN with a luminosity\ngreater than approximately 20% that of SN 1998bw underlying the GRB.\nWe note, however, that we cannot rule out the existence of a more\ntypical SN Ib/c, such as SN 1994I.  We strongly recommend that\nobservers planning a search for a SN underneath a GRB afterglow do\nnot assume that the SN will be as luminous as SN 1998bw.\n\nA more detailed analysis of the data is in progress.\n\nThis message may be cited.\n\n[GCN ED NOTE (06Mar02):  A type was corrected: \"6.7 x 10^51\" to \"6.7 x 10^50\".]",
  "circularId": 1259,
  "createdOn": 1015379695000,
  "email": "pap@srl.caltech.edu",
  "subject": "GRB 010921: HST Observations",
  "submitter": "Paul Price at RSAA, ANU at CIT  <pap@srl.caltech.edu>",
  "eventId": "GRB 010921"
}