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GCN Circular 6774

GRB 070809: Confirmation of optical transient
2007-09-08T22:39:45Z (17 years ago)
Daniel Perley at U.C. Berkeley <>
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

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.
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