GCN Circular 5282
Subject
GRB 060614: SMARTS host galaxy observations
Event
Date
2006-06-28T19:09:48Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS consortium,
report:
Continuing ANDICAM observations (see GCN 5259 for observing details) of
the afterglow of GRB 060614 (GCN 5255, Holland et al.) reveal the host
galaxy of the GRB in the I-band. Preliminary photometry in comparison with
several USNO B1.0 stars reveals that the host galaxy maintains a constant
brightness of I = 21.9 +/- 0.2 magnitudes between observations at
2006-06-19 07:36 UT and 2006-06-27 09:31 UT.
Images from four separate epochs (mid-exposure times of 2006-06-19 07:36
UT, 2006-06-21 07:22 UT, 2006-06-25 09:43 UT and 2006-06-27 09:31 UT) were
combined to produce a single J-band image but the host galaxy of GRB
060614 is not detected in this image down to a limiting magnitude of
J > 20.3+/-0.2 (based on two 2MASS standard stars).
Such a combined image was also produced in the I-band. The centroid of
the host galaxy was then compared to the centroid of the afterglow (imaged
at 2006-06-15 04:16 UT). The centroid of the afterglow appears 0.32" South
and 0.09" East of the host galaxy centroid. At a redshift of z=0.125
(GCN 5276, Fugazza et al.), and assuming H_o=71 km s^-1 Mpc^-1,
Omega_M=0.27 and Omega_Lambda=0.73, the projected distance between the
afterglow and the center of the host galaxy is 0.73 kpc.
Our 2006-06-27 09:31 UT observations correspond to ~13 days post-burst, or
~12 days in the host galaxy rest-frame. By this time post-burst in the
case of several other low-redshift GRBs (GRB 980425/SN 1998bw, GRB
031203/SN 2003lw and GRB 060218/SN 2006aj), the light from the associated
SNe was already clearly visible, yet no brightening is yet observed in the
host galaxy of GRB 060614 (see also GCN 5277, Fynbo et al.). Based on SN
1998bw and SN 2006aj, the expected absolute magnitude for a SN associated
with GRB 060614 would be I~-19.0. There is only a negligible amount of
Galactic extinction toward GRB 060614, so if a SN associated with GRB
060614 is not intrinsically underluminous but is being masked by
extinction, then that extinction must be due to dust in the host galaxy.
If we conservatively assume that half a magnitude increase in the
brightness of the host galaxy would have been detected in our I image,
then the absolute magnitude (uncorrected for absorption) of the SN must be
less than approximately -16.3. If this SN is not intrinsically
significantly dimmer than SN 1998bw or SN 2006aj, then this implies an
extinction in the host galaxy of at least 2.7 magnitudes in I, or A_V=5.6
assuming standard reddening with R_V=3.1.