GCN Circular 14490

Patrick Wiggins (Stansbury Park, Utah, United States) reports the following 
optical observations of the error box of GRB 130427A (GCN Circ #14448,
Maselli et al.) to the AAVSO International High Energy Network:

P. Wiggins reports three hours of time-series photometry of the bright GRB 
130427A (Maselli et al., GCN Circ. #14448; Elenin et al., GCN Circ. # 
14450). Wiggins used a 0.35-m C-14 f/5.5 telescope with an SBIG ST-10XME 
camera and clear filter located in Stansbury Park, Utah.  Observations 
commenced 2013 April 27 08:05:12 UT -- less than 20 minutes post trigger 
-- and continued through 11:10:06 UT.  The first four observations were 
made with 60-second exposure times, which were found to be close to 
saturation; subsequent exposure times were 30 seconds.  The transient was 
detected by visual inspection of the first frame, and found to be very 
bright.  Time-series observations were begun immediately.

Thirty-three images of the field were taken, and the resulting light curve 
is as follows.  All magnitudes are taken with respect to the comparison 
star GSC 01984-00021, which has an r-magnitude of 12.553 (APASS DR7, 
http://www.aavso.org/apass ); the resulting magnitudes should be 
interpreted as through a clear filter with r'-band zero point.  Note that 
the first four magnitudes with integration times of 60 seconds may be 
saturated.  All times are given as the mid-point of the exposure, UT on 
2013 April 27, and T(0)+h is hours since trigger (07:47:57 UT):

     Obs. UT	T(0)+h	Exp. time	magn.	mag.err.
08:05:41.529	0.296	   60.00	13.108	 0.006
08:06:57.779	0.317	   60.00	13.194	 0.007
08:14:16.467	0.439	   60.00	13.557	 0.009
08:27:07.951	0.653	   60.00	13.995	 0.013
08:40:35.701	0.877	   30.00	14.304	 0.024
08:46:36.857	0.978	   30.00	14.413	 0.027
08:50:51.998	1.049	   30.00	14.47	 0.029
08:55:17.311	1.122	   30.00	14.546	 0.030
09:00:52.545	1.215	   30.00	14.623	 0.033
09:06:26.014	1.308	   30.00	14.684	 0.035
09:11:59.514	1.401	   30.00	14.731	 0.038
09:17:33.139	1.493	   30.00	14.792	 0.041
09:23:06.748	1.586	   30.00	14.829	 0.043
09:28:40.357	1.679	   30.00	14.969	 0.050
09:34:18.373	1.773	   30.00	14.957	 0.050
09:39:51.873	1.865	   30.00	14.911	 0.050
09:45:25.545	1.958	   30.00	15.025	 0.055
09:50:59.404	2.051	   30.00	15.158	 0.064
09:56:32.982	2.143	   30.00	15.104	 0.064
10:02:06.529	2.236	   30.00	15.22	 0.073
10:07:40.154	2.329	   30.00	15.138	 0.071
10:13:13.732	2.421	   30.00	15.249	 0.080
10:15:01.029	2.451	   30.00	15.219	 0.078
10:20:47.498	2.547	   30.00	15.302	 0.088
10:26:21.123	2.64	   30.00	15.424	 0.099
10:31:54.732	2.733	   30.00	15.387	 0.100
10:37:28.451	2.825	   30.00	15.247	 0.091
10:43:02.248	2.918	   30.00	15.512	 0.123
10:48:35.811	3.011	   30.00	15.496	 0.124
10:54:09.561	3.103	   30.00	15.517	 0.128
10:59:43.279	3.196	   30.00	15.633	 0.150
11:05:19.092	3.289	   30.00	15.555	 0.150
11:10:20.982	3.373	   30.00	15.48	 0.153

The AAVSO International High Energy Network is supported through the
AAVSO Endowment Fund.  We thank the Charles Curry Foundation and
NASA for past support.