TITLE:   GCN CIRCULAR
NUMBER:  18559
SUBJECT: GRB 151027A: Mondy optical observations
DATE:    15/11/04 17:58:29 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the Swift GRB 151027A  (Maselli  et al., GCN 18478) with 
AZT-33IK telescope of Sayan observatory (Mondy) on several epochs.   We 
obtained
images in R-filter  on Oct., 27-- Nov., 1 .  The afterglow (Maselli et al., 
GCN 18478; Zheng and  Filippenko, GCN 18479) is clearly detected in each 
epoch. Coordinates of the afterglow are (J2000) 18 09 56.66 +61 21 13.0 with 
uncertainties of 0.3 arcsec in each coordinate. We also detected the 
USNO-B1.0 source mentioned in GCN 18510 (Dichiara et al.) in a position 
(J2000) 18 09 56.44 +61 21 10.8 with uncertainties of 0.3 arcsec in each 
coordinate.

Preliminary photometry of the afterglow  on October-29 -- November, 1 is 
following

Date                UT start   t-T0        Filter   Exp.       OT       Err.
                                        (mid, days)        (s)


2015-10-29   13:18:41  2.4082   R         55*60   19.84  0.05
2015-10-30   12:11:18  3.3736   R         78*60   20.32  0.06
2015-10-31   12:47:18  4.3958   R         41*120 21.25  0.07
2015-11-01   12:28:18  5.3694   R        19*120  21.50  0.12

The photometry is based on nearby USNO-B1.0 stars
USNO-B.1_id R2
1513-0237223 16.66
1513-0237170 15.58
1513-0237251 16.81
1513-0237270 16.78

Late time photometry could be influenced by the nearby USNO-B1.0 source.

The overall light curve of our observations as well as photometry reported 
in GCNs 18480, 18521,18558 can be found in
http://grb.rssi.ru/GRB151027A/GRB151027A_lc.png