GCN Circular 7705
Subject
GRB 080507: E Pur Si Muove!
Event
Date
2008-05-09T23:48:40Z (19 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, C. Hoegner, R. Filgas and S. Klose (TLS Tautenburg) report:
We observed again the location of the candidate afterglow (Kann et al.,
GCN 7701) of the AGILE GRB 080507 (Lapshov et al., GCN 7697), which was
also detected as a bright X-ray source (Mangano et al., GCN 7699). We
obtained 20 x 180 sec images in the R band under excellent atmospheric
conditions but with elevated sky background due to twilight and the waxing
moon. The resulting stacked image is roughly half a magnitude deeper than
the image from the first epoch (23.5 vs. 23, respectively).
We find that the candidate afterglow has significantly faded over the
course of a day. Using the same comparison star as Kann et al. (GCN 7701),
we find:
time (days) Rc dRc
2.5578 22.69 0.15
We also use SExtractor (Bertin & Arnouts 1996) to derive magnitudes, and
find Rc = 21.95 +/- 0.14 and Rc = 22.65 +/- 0.20 in the first and second
epoch, respectively, in accordance with our other results.
This fading behaviour is in contrast to the plateau phase or even rising
behaviour reported from UVOT White images (Breeveld & Baumgartner, GCN
7702), which may imply a non-monotonic light curve evolution.
With the clear detection of fading, we consider the identification of this
source as the optical afterglow of GRB 080507 as secure.
Finally, we note that GRB 080507 was also detected by INTEGRAL SPI-ACS,
showing a flat-topped structure, with possible multiple peaks, of 40
seconds duration, in full agreement with the AGILE report (Lapshov et al.,
GCN 7697). The public light curve can be found here:
http://isdc.unige.ch/cgi-bin/cgiwrap/~beck/ibas/spiacs/ibas_acs_web.cgi/
?trigger=2008-05-07T07-44-58.8545-18523-00007-0
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