TITLE:   GCN CIRCULAR
NUMBER:  7233
SUBJECT: GRB 080129: Gemini-South photometry
DATE:    08/01/29 11:48:14 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>

D. A. Perley and J. S. Bloom (UC Berkeley) report on behalf of the 
GRAASP collaboration:

Preliminary photometry of our first series of r-band observations of the 
candidate afterglow of GRB 080129 (Immler et al., GCN 7226; Bloom, 7229) 
yields the following magnitudes, calibrated using three DSS stars*:

t=44 min: R = 22.93 +/- 0.06
t=50 min: R = 22.86 +/- 0.05
t=56 min: R = 22.78 +/- 0.04
t=62 min: R = 22.56 +/- 0.04
t=68 min: R = 22.87 +/- 0.05

As these magnitudes are approximately consistent with the value reported 
by Kruehler et al. (GCN 7231/7232) we do not confirm general fading 
behavior of this source over the interval of our observations. 
However, we note that the fourth exposure shows statistically 
significant evidence of a short-lived rebrightening.  While an 
instrumental cause has not been ruled out, given the location in the 
Galactic plane of the source and the very slow fading reported by 
Kruehler et al. (0.5 mag from 4 to ~94 minutes, atypical of extragalactic 
GRBs), it is possible that the GRB may be an analog of GRB 070610 / 
SWIFT J195509.6+261406 (Pagani et al., GCN 6489; Kasliwal et al. 2007, 
arXiv:0708.0226), which showed extensive short-time scale early-time 
variability above a nearly-constant baseline.  Further observations 
(including rapid-time-series optical observations), and further analysis 
of the X-ray afterglow, are encouraged to further investigate the nature 
of this source.

---

*Calibration stars are:

ra            dec            R2
07:01:10.5033 -07:50:24.020  17.130
07:01:07.7333 -07:51:24.620  17.040
07:01:04.7193 -07:50:46.690  17.310

[GCN OPS NOTE(29jan08): Per author's request, the "Greiner" citation was changed
to "Kruehler".]