{
  "bibcode": "2013GCN.14182....1V",
  "body": "A. Volnova (SAI MSU/IKI), I. Korobtsev (ISTP), E. Klunko (ISTP),   A. \nPozanenko (IKI) report on behalf of  larger GRB  follow-up collaboration:\n\nWe observed the field of the Swift GRB 130131A (Grupe et al., GCN 14156) \nwith AZT-33IK telescope of Sayan observatory (Mondy). We took several \nimages in R-filter of 60 s exposure on Jan. 31, between (UT) \n14:12:36-15:36:53 under favorable weather conditions with a FWHM of \nabout  2.5\". In the stacked images we detected a source which is \ncoincident with the source reported by Tanvir et al. (GCN 14157). The \nphotometry based on SDSS DR8 is the following:\n\n  t_start,      T0+ (mid), filter,  exp.,   OT+/-err      UL (3 sigma)\n  (UT)          d                   s\n\n  14:12:36      0.01640    R       10x60    22.5 +/-0.35  22.4\n  14:12:36      0.04053    R       79x60    23.4 +/-0.25  23.5\n\nTaken coincidence with source detected in IR (Tanvir et al. GCN 14157) \nand fading nature of the source we suggest that we detect OT of GRB \n130131A. The detection in R filter confirms that the GRB 130131A is not\nan extreme redshift event (Tanvir et al. GCN 14175). Also we compared \nfluxes in X-ray and optic at ~0.016 days after trigger and found that \nthe GRB 130131A can be considered as  optically dark burst following the \nboth criteria (Jakobsson et al., 2004; van der Horst et al., 2009).\n\nThe stars used for photometry and assumed R mags:\n\nJ112419.01+480710.6 11:24:19.01 +48:07:10.7 R = 18.93\nJ112414.86+480528.8 11:24:14.86 +48:05:28.9 R = 18.77\nJ112419.60+480357.4 11:24:19.61 +48:03:57.5 R = 20.32\n\nThe finding chart of the stacked image can be found in \nhttp://grb.rssi.ru/GRB130131A/GRB130131A_130131_AZT33IK.png",
  "circularId": 14182,
  "createdOn": 1360182468000,
  "email": "apozanen@iki.rssi.ru",
  "subject": "GRB 130131A: optical observation in Mondy observatory",
  "submitter": "Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>",
  "eventId": "GRB 130131A"
}