GCN Circular 6451
Subject
GRB 070521: Keck imaging
Date
2007-05-22T07:49:54Z (17 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, J. S. Bloom (UC Berkeley), J. X. Prochaska (UC Santa
Cruz), S. Stanford (LLNL), M. Brodwin (JPL), and N. R. Butler (UCB) report:
Starting at 13:21:22 UT (2007-05-21), we imaged the field of GRB 070521
(GCN 6431) in V and R band with the Keck I telescope (+ LRIS), in a
series of five exposures of 300 seconds each. The host galaxy candidate
of Hattori et al. (GCN 6444, "S1") is clearly detected, as is a second
source ("S2") at the edge of the XRT error circle (Guidorzi et al., GCN
6431). We also detect a third, extended source ("S3") further to the
south, not consistent with the preliminary XRT position reported by
Guidorzi et al. but consistent with our preliminary re-analysis of the
XRT data.
The positions of these sources (J2000) are:
S1: 16:10:38.562 +30:15:27.50
S2: 16:10:38.734 +30:15:31.38
S3: 16:10:38.754 +30:15:21.57
The astrometric uncertainty is about 0.3" in each coordinate.
Preliminary aperture magnitudes of these sources, calibrated with
respect to the SDSS magnitudes from Cool et al. (GCN 6432) using the
Lupton transform [1], are:
S1: V = 25.46 +/- 0.12 , I = 23.88 +/- 0.12
S2: V = 25.98 +/- 0.20 , I = 24.26 +/- 0.16
S3: V = 26.63 +/- 0.39 , I = 24.39 +/- 0.17
These magnitudes are not corrected for Galactic extinction, which the
NED extinction calculator [2] estimates to be E(B-V) = 0.027, or A_V =
0.09, A_I = 0.05, in this direction.
An image of the field is located at:
http://lyra.berkeley.edu/~dperley/070521/070521keckI.png
http://lyra.berkeley.edu/~dperley/070521/070521keckI_clean.png
---
[1] http://www.sdss.org/dr5/algorithms/sdssUBVRITransform.html#Lupton2005
[2] http://nedwww.ipac.caltech.edu/forms/calculator.html
