GCN Circular 9211
Subject
GRB090418A Rc-band photometry
Date
2009-04-23T19:03:44Z (16 years ago)
From
Arne A. Henden at AAVSO <arne@aavso.org>
A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3),
D. Terrell (SwRI), and W. Cooney (SRO) report:
We obtained photometry of the GRB090418A afterglow
reported by Chornock et al. (GCN 9148) using the Sonoita
Research Observatory (SRO) 35cm telescope in southern
Arizona, utilizing an automatic VOevent trigger. The
Rc-band exposures began about 2 minutes after the burst
and continued until twilight. Ten 60-second and five
180-second exposures were acquired.
Astrometry of the afterglow from several images and
using UCAC as the reference catalog yields coordinates:
17:57:15.151 +33:24:20.93 J2000 (+/- 50mas)
Photometry, assuming that the star at
17:57:42.53 +33:25:47.2
has an R magnitude of 13.12
UT(mid) delT exp Rc err
11.1728 162 60 15.802 0.044
11.1919 231 60 16.185 0.048
11.2111 300 60 16.500 0.043
11.2303 369 60 16.818 0.058
11.2494 438 60 17.019 0.066
11.2686 507 60 17.249 0.067
11.2878 576 60 17.440 0.063
11.3069 645 60 17.605 0.105
11.3261 714 60 17.680 0.089
11.3450 782 60 17.855 0.115
11.3958 965 180 18.007 0.104
11.6522 1888 180 18.778 0.129
11.7067 2084 180 18.919 0.138
11.7592 2273 180 18.960 0.142
11.8114 2461 180 18.891 0.196
Where delT is the time in seconds from the burst (Mangano et al.,
GCN 9149), and the exposure is in seconds. The optical afterglow
candidate is in the filter reflection halo from HD163948,
a 6.9mag star about 2arcmin distant, so the last
few magnitudes may have a systematic bias.
We note that this field was not calibrated by SDSS through DR6.
We will perform a BVRI calibration over the next few nights.