{
  "bibcode": "2000GCN...751....1V",
  "body": "P.M. Vreeswijk, A. Fruchter, H. Ferguson and C. Kouveliotou report for\na larger HST GRB Collaboration:\n\nThe afterglow of GRB 991216 (c.f. Kippen et al. 1999 ; Uglesich et\nal. 1999) was observed using HST/STIS at approximately UT 2000 April\n17.6 through the clear (50CCD) and long pass (LP) filters, each for a\ntotal of 4790s.  The pipeline reduced images were drizzled onto output\nimages with pixels one-half native scale, or approximately 0.\"025 on a\nside.\n\t\nWe have projected the OT position from an early VLT image taken 1.5\ndays after the burst, to the frame of the HST drizzled images. Four\nbright nearby reference stars were used, and the estimated error in\nthe resulting position is 0.\"1, corresponding to 4 pixels.\n\nThe position coincides with the visible extent of a faint galaxy,\npresumably the host of GRB 991216. The galaxy appears irregular, with\na diameter of about 0.\"3. Another, probably separate, faint galaxy is\nlocated 0.\"4 to the southwest of the afterglow position.  These two\nobjects may explain the presence of two MgI absorption line systems in\nthe VLT spectrum of 991216 (Vreeswijk et al. 1999), while one of the\nother galaxies visible at a separation of about 2\" could potentially\nbe responsible for the third absorption line system.\n\nUsing an aperture of diameter 0.\"4, we measure R=26.9 +/- 0.2 for the\nprobable host of GRB 991216. The galaxy to the southwest has R = 26.1\n+/- 0.2 inside an aperture of diameter 0.\"6.  The large errors reflect\nthe difficulty of matching the colors of these objects -- all objects\nin the field are quite red, perhaps indicating that the foreground\nextinction is even higher than the A(R)=1.6 mags predicted by the\nSchlegel et al. (1998) model.  Additionally, it is probable that the\nsmall apertures used underestimate the total magnitudes of these\ngalaxies by at least a couple of tenths.\n\nThe transient afterglow may still be present in these observations,\nbut the low signal to noise does not allow unambiguous identification\nof the bright patch at the edge of the galaxy as a point source.  We\nestimate that any remaining OT is no brighter than R=27.6.  Assuming\nthe single power law decay index, alpha = -1.36, of Garnavich et\nal. (2000), the afterglows expected magnitude at the time of our\nobservations is R ~ 27 (not corrected for Galactic extinction). Our\nobservations therefore suggest a break in the light curve, as already\ninferred by Halpern et al. (2000). A supernova of type SN1998bw at a\nredshift of z=1.02 would have R>30 at the epoch of our observations.\n\nImages of the host and surrounding region can be found at:\nhttp://www.stsci.edu/~fruchter/GRB/991216\n\nReferences:\n\nGarnavich et al. 2000, ApJ, in press, preprint astro-ph/0003429\nHalpern et al. 2000, ApJ, in press, preprint astro-ph/0006206\nKippen et al. 1999, GCN Circ. No. 463\nSchlegel et al. 1998, ApJ, 500, 525\nUglesich et al. 1999, GCN Circ. No. 472\nVreeswijk et al. 1999, GCN Circ. No. 496",
  "circularId": 751,
  "createdOn": 963825482000,
  "email": "pmv@astro.uva.nl",
  "subject": "GRB 991216, HST/STIS observations",
  "submitter": "Paul Vreeswijk at U of Amsterdam  <pmv@astro.uva.nl>",
  "eventId": "GRB 991216"
}