TITLE:   GCN CIRCULAR
NUMBER:  15150
SUBJECT: GRB 130831A: Montarrenti Observatory optical observations
DATE:    13/09/01 01:07:49 GMT
FROM:    Simone Leonini at Monarrenti Obs  <s.leonini@iol.it>

Simone Leonini, G. Guerrini, P. Rosi and L.M. Tinjaca Ramirez (Montarrenti 
Observatory, Siena, Italy) report:

We observed the optical afterglow of GRB 130831A (Swift trigger 568849, Hagen 
et al., GCN Circ. 15139) and slow fading over the four hours span of 
observations with the automatic 0.53m RC telescope + U47 detector at 
Montarrenti Observatory (Siena, Italy, IAU code C88).

The observations were started at 2013-08-31 20:18:04 UT (approximately 7 hours 
post-burst) and continued to 00:29:36 UT on 2013-09-01 stacking 2 unfiltered 
CCD exposures of 60s for each run.

The OT was detected in all frames. The resulting time-series are as follows:

2013 Aug 31.84588 UT R=18.22 +/- 0.21 
2013 Aug 31.90427 UT R=18.55 +/- 0.21
2013 Aug 31.94019 UT R=18.47 +/- 0.22
2013 Aug 31.96977 UT R=18.63 +/- 0.23
2013 Aug 31.99955 UT R=18.95 +/- 0.22
2013 Sep 01.02056 UT R=19.09 +/- 0.21


Magnitudes were obtained using Astrometrica software using USNO-B1 catalogue 
for positions and photometry. An ensemble between 38 and 66 stars were used for 
the magnitude comparison.

The position of the GRB (within the error box given by Swift) is the 
following:

RA    (J2000.0)  23h 54m 29.90s +/-0.13
Decl. (J2000.0) +29° 25' 46.8"  +/-0.14

The message may be cited.