TITLE:   GCN CIRCULAR
NUMBER:  14182
SUBJECT: GRB 130131A: optical observation in Mondy observatory
DATE:    13/02/06 20:27:48 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Volnova (SAI MSU/IKI), I. Korobtsev (ISTP), E. Klunko (ISTP),   A. 
Pozanenko (IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of the Swift GRB 130131A (Grupe et al., GCN 14156) 
with AZT-33IK telescope of Sayan observatory (Mondy). We took several 
images in R-filter of 60 s exposure on Jan. 31, between (UT) 
14:12:36-15:36:53 under favorable weather conditions with a FWHM of 
about  2.5". In the stacked images we detected a source which is 
coincident with the source reported by Tanvir et al. (GCN 14157). The 
photometry based on SDSS DR8 is the following:

  t_start,      T0+ (mid), filter,  exp.,   OT+/-err      UL (3 sigma)
  (UT)          d                   s

  14:12:36      0.01640    R       10x60    22.5 +/-0.35  22.4
  14:12:36      0.04053    R       79x60    23.4 +/-0.25  23.5

Taken coincidence with source detected in IR (Tanvir et al. GCN 14157) 
and fading nature of the source we suggest that we detect OT of GRB 
130131A. The detection in R filter confirms that the GRB 130131A is not
an extreme redshift event (Tanvir et al. GCN 14175). Also we compared 
fluxes in X-ray and optic at ~0.016 days after trigger and found that 
the GRB 130131A can be considered as  optically dark burst following the 
both criteria (Jakobsson et al., 2004; van der Horst et al., 2009).

The stars used for photometry and assumed R mags:

J112419.01+480710.6 11:24:19.01 +48:07:10.7 R = 18.93
J112414.86+480528.8 11:24:14.86 +48:05:28.9 R = 18.77
J112419.60+480357.4 11:24:19.61 +48:03:57.5 R = 20.32

The finding chart of the stacked image can be found in 
http://grb.rssi.ru/GRB130131A/GRB130131A_130131_AZT33IK.png