GCN Circular 1781
Subject
GRB 021211: Probable Host and Underlying Supernova
Date
2002-12-30T00:11:03Z (22 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
Andrew Fruchter (STScI), Andrew Levan (U. Leicester/STScI), Paul Vreeswijk
(ESO), Stephen T. Holland (Notre Dame) and Chryssa Kouveliotou (MSFC)
report for the GOSH collaboration:
We have observed the field of GRB 021211 with the Advanced Camera for
Surveys (ACS) on HST in the F435W (B), F606W (wide V) and F814W (I)
filters and the NICMOS camera using the F160W (H) filter on 18 December,
and again using the F606W and F814W filters on 25 and 24 December,
respectively.
We find that the source at the location of the optical afterglow (GCN
1731) is resolved in the ACS images with a FWHM of approximately 0."14,
or approximately twice that of the native ACS resolution, suggesting that
the light is primarily from the GRB's host. This is further supported
by the colors of the object. In the 18 December data we find that
in AB magnitudes, F435W - F606W ~ F814W - F160W ~ 0.1 mag; however,
F606W - F814W = 0.95 +/- 0.1 and F606W = 25.26 +/- 0.2 (where we have
used conservative errors due to uncertainties in the calibration).
These colors are roughly consistent with the observation of the 4000A
break in a blue galaxy at approximately z=0.8, the host may therefore
be interacting with the galaxy to the North East at z=0.800 +- 0.001
(GCN 1756). However the color is also consistent with the 1216A break
at around z=5.
When we examine the flux within a few pixels of the peak brightness of
the object (which corresponds well with the location of the afterglow in
early CTIO images, GCN 1758) the flux in the F606W band falls between
the two epochs by 0.07 +/- 0.03 mags, but rises in F814W by about 0.3
+/- 0.07 mags. This may suggest we are seeing the first signs of an
underlying supernova, which like the galaxy, would be expected to show
a break between the F606W and F814W bands if it were at approximately
z=0.8. However, given its present magnitude, at maximum any underlying
supernova will likely be significantly less bright than SN1998bw, and
be only a fraction of the host light.
Using the x-ray fluence of GCN 1734 and assuming a "standard" candle
gamma-ray energy of 5e50 erg for GRB021211, we derive a beaming angle
of 101 degrees at z=0.8 or, alternatively of 17 degrees at z=5. If GRB
021211 does originate from z=0.8 (which would be the case if the observed
rebrightening is due to a supernova), it is likely an underluminous
event in gamma-rays, similar to GRB980425.
Images of the field can be found at
http://www.stsci.edu/~fruchter/GRB/021211
Further HST observations are planned.