GCN Circular 6774
Subject
GRB 070809: Confirmation of optical transient
Event
Date
2007-09-08T22:39:45Z (18 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley (UC Berkeley), C. C. Thoene (DARK, UCB), and J. S. Bloom
(UCB) report:
After our initial observations (GCN 6739) of the possibly short GRB
070809 (Palmer et al., GCN 6728), we obtained a second series of imaging
the following night using the Keck I telescope (+LRIS).
We imaged the field for a total of 640s (R) and 880s (g) simultaneously
in a series of images starting at 06:20:17 UT (2007-08-11) at very high
airmass.
The point-like source reported in GCN 6739 visible the first night has
significantly faded, and is detectable only at the 3 sigma level in
R-band and is undetected in g-band. Using an absolute calibration
relative to Landolt standard stars, we calculate magnitudes of this
source of:
UT (mid-time) t_burst (hr) magnitude
2007-08-10 06:35 11.21 R = 24.1 +/- 0.2
g = 25.7 +/- 0.2
2007-08-11 06:31 35.14 R = 25.0 +/- 0.3
g > 26.0 (3-sigma)
We caution that the source is very close to a bright (R~13) star and
slightly blended with a diffraction spike in our imaging. This and the
very high airmass of the observations may create additional
uncertainties in the photometry.
In addition, we acquired a 2x600s spectrum of the nearby edge-on galaxy
noted in GCN 6739 during twilight starting at 05:46 UT (2007-08-11),
covering the wavelength range from about 3800 to 9200 AA. No obvious
emission lines are detected.