{
  "bibcode": "2002GCN..1781....1F",
  "body": "Andrew Fruchter (STScI), Andrew Levan (U. Leicester/STScI), Paul Vreeswijk\n(ESO), Stephen T. Holland (Notre Dame) and Chryssa Kouveliotou (MSFC)\nreport for the GOSH collaboration:\n\nWe have observed the field of GRB 021211 with the Advanced Camera for\nSurveys (ACS) on HST in the F435W (B), F606W (wide V) and F814W (I)\nfilters and the NICMOS camera using the F160W (H) filter on 18 December,\nand again using the F606W and F814W filters on 25 and 24 December,\nrespectively.\n\nWe find that the source at the location of the optical afterglow (GCN\n1731) is resolved in the ACS images with a FWHM of approximately 0.\"14,\nor approximately twice that of the native ACS resolution, suggesting that\nthe light is primarily from the GRB's host.  This is further supported\nby the colors of the object.  In the 18 December data we find that\nin AB magnitudes, F435W - F606W ~ F814W - F160W ~ 0.1 mag;  however,\nF606W - F814W = 0.95 +/- 0.1 and F606W = 25.26 +/- 0.2 (where we have\nused conservative errors due to uncertainties in the calibration).\nThese colors are roughly consistent with the observation of the 4000A\nbreak in a blue galaxy at approximately z=0.8, the host may therefore\nbe interacting with the galaxy to the North East at z=0.800 +- 0.001\n(GCN 1756). However the color is also consistent with the 1216A break\nat around z=5.\n\nWhen we examine the flux within a few pixels of the peak brightness of\nthe object (which corresponds well with the location of the afterglow in\nearly CTIO images, GCN 1758) the flux in the F606W band falls between\nthe two epochs by 0.07 +/- 0.03 mags, but rises in F814W by about 0.3\n+/- 0.07 mags.   This may suggest we are seeing the first signs of an\nunderlying supernova, which like the galaxy, would be expected to show\na break between the F606W and F814W bands if it were at approximately\nz=0.8. However, given its present magnitude, at maximum any underlying\nsupernova will likely be significantly less bright than SN1998bw, and\nbe only a fraction of the host light.\n\nUsing the x-ray fluence of GCN 1734 and assuming a \"standard\" candle\ngamma-ray energy of 5e50 erg for GRB021211, we derive a beaming angle\nof 101 degrees at z=0.8 or, alternatively of 17 degrees at z=5. If GRB\n021211 does originate from z=0.8 (which would be the case if the observed\nrebrightening is due to a supernova), it is likely an underluminous\nevent in gamma-rays, similar to GRB980425.\n\nImages of the field can be found at\n\nhttp://www.stsci.edu/~fruchter/GRB/021211\n\nFurther HST observations are planned.",
  "circularId": 1781,
  "createdOn": 1041207063000,
  "email": "anl@star.le.ac.uk",
  "subject": "GRB 021211: Probable Host and Underlying Supernova",
  "submitter": "Andrew Levan at U.of Leicester  <anl@star.le.ac.uk>",
  "eventId": "GRB 021211"
}