{
  "bibcode": "1999GCN...403....1H",
  "body": "GRB 990712 Late Optical Decay and Host Galaxy\n\n\nJ. Hjorth (University of Copenhagen), J. Fynbo (University of Aarhus and ESO),\nA. Dar (Technion, Haifa and CERN), F. Courbin (Universidad Catolica de Chile)\nand P. Moller (ESO) report:\n\n\"We have obtained a 4-min R-band exposure of the optical afterglow + host\ngalaxy of GRB 990712 (Bakos et al., GCN #387; IAUC 7225; Hjorth et al., \nGCN #389; Kemp & Halpern GCN #402) with the ESO 8.2-m Antu telescope on \n12.232 August 1999 UT. The OT + host has R = 21.71 +- 0.03 on the PLANET \nphotometric system and is slightly extended in seeing FWHM = 1.2\" as revealed \nby (i) faint but significant residuals after fitting and subtraction of a \npoint source (ii) deconvolution (Magain et al., ApJ, 494, 452, 1998). The host \ngalaxy is oriented roughly E-W. The decay slope of the optical transient \n(-1.03) and host galaxy magnitude (R = 21.76) are consistent with the \nprediction of Hjorth et al. (GCN #389) when correcting for the erroneous date \nof the first data point of Bakos et al. (IAUC 7225) and with the findings of \nKemp & Halpern (GCN #402). The R band light curve can also be fit by a galaxy \n(R = 21.92) and an OT with initial power-law decay (-1.00) that is taken over \nlater by a ``standard candle'' SN (Dar, astro-ph/9902017; Bloom et al., \nastro-ph/9905301; Dar, GCN #346; Reichart, astro-ph/9906079; Galama et al., \nastro-ph/9907264) like 1998bw (Galama et al., Nature, 395, 670, 1998; \nMcKenzie & Schaefer, astro-ph/9904397) at the redshift of the GRB (z = 0.43; \nGalama et al., GCN #388). The HST observation of GRB 990712 scheduled for \nAugust 29 can distinguish between the two models which predict OT magnitudes \nof R = 25.80 in the simple power-law model and R = 24.20 in the power law + SN \nmodel (or R(SN) = 24.58 if the power law decline steepened before August 29). \nThe takeover by a SN light curve would also result in a dramatic reddening of \nthe afterglow colours. Alternatively, the two models can be discriminated by \nhigh-precision R band observations obtained around 1 August 1999 UT or by\nlate-time observations of the host galaxy brightness. The VLT image (before and \nafter point source subtraction or deconvolution) and the R-band light curves \nfor the two models are posted at http://www.astro.ku.dk/~jens/grb990712/ .\"",
  "circularId": 403,
  "createdOn": 935082681000,
  "email": "jens@astro.ku.dk",
  "subject": "GRB 990712 Late Optical Decay and Host Galaxy",
  "submitter": "Jens Hjorth at U.Copenhagen  <jens@astro.ku.dk>",
  "eventId": "GRB 990712"
}