{
  "bibcode": "1998GCN....30....1B",
  "body": "Optical Observations of GRB 970508:                               #030\n\nJ. S. Bloom, S. R. Kulkarni, S. G. Djorgovski, Caltech and\nD. A. Frail, NARO report on behalf of the Caltech GRB effort:\n\n\"Optical follow-up of GRB 970508 on the Keck-II 10m was conducted on\nthe nights of Nov 28-29, 1997 and Feb 22-23, 1998. In both cases,\nimaging observations were obtained with the Low Resolution Imaging\nSpectrograph (LRIS).  Coincident with the position of the optical\ntransient, a faint source is easily detected in both B- and R-bands.\nDifferencing photometry with a number of field objects provided by V.\nSokolov (see their paper at http://xxx.lanl.gov/astro-ph/9802341),\nsuggest that the light curve has levelled off from the initial\npower-law decline seen from 2-100 days from the time of the burst\n(Sokolov et al. ibid).\n\nWe find:\nB (UT Nov 29.6, 1997) = 26.32 +/- 0.26 mag (integ., 2400s),\nB (UT Feb 23.4, 1998) = 26.27 +/- 0.14 mag (integ., 2400s),\nR (UT Nov 28.6-29.5, 1997) =  25.09 +/- 0.14 mag (integ., 5400s), and\nR (UT Feb 22.4, 1998) =  25.29 +/ 0.16 mag. (integ., 3600 s).\nThe systematic uncertainty of the Sokolov photometric zero-point (0.05\nmag) is not included in the error analysis.  Had the power-law decline\ncontinued the predicted brightness at the time of observations would be\n[B,R] 26.65,25.63 (Nov) and 27.11,26.07 (Feb).  The 1-sigma errors for\nthe power-law light curve are estimated at 0.25 and 0.2 for B and R,\nrespectively, at each epoch. At the second epoch, then, the source is\nsignificantly brighter then predicted by ~0.8 mags in each band.\n\nThus, although the object does not appear extended (consistent\nwith the HST findings of Fruchter et al. IAUC 6674) beyond that which\nis expected from the seeing (~0.8\"), we interpret the level-off as due\nto the faint host galaxy--itself responsible for the persistent [OII]\nemission. \n\nIn fact, the lack of extent of the galaxy may be connected with its\npreviously inferred underluminous nature (Fruchter et al., and\nNatarajan et al. 1997).  Furthermore, the B-R color (+1) is consistent\nwith an irregular galaxy at z=0.8 (Fukugita et al. 1995).\n\nWe thank V. Sokolov for collegial help in providing photometry of\nsecondary stars fainter than those reported in their Huntsville\nposter.\n\nThis circular is a citable reference.\"",
  "circularId": 30,
  "createdOn": 0,
  "email": "circulars@gcn.nasa.gov",
  "subject": "Untitled",
  "submitter": "circulars@gcn.nasa.gov"
}