TITLE:   GCN CIRCULAR
NUMBER:  21419
SUBJECT: GRB 170728B: TShAO, SAO RAS and AbAO optical observations
DATE:    17/08/07 10:23:04 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Volnova (IKI),  A. Kusakin (Fesenkov Astrophysical Institute), A.S. 
Moskvitin (SAO RAS), O.I. Spiridonova (SAO RAS),  R. Inasaridze (AbAO), I. 
Reva (Fesenkov Astrophysical Institute),  E. Mazaeva (IKI), A. Pozanenko 
(IKI)   report on behalf of larger GRB follow-up collaboration:

We observed the field of the Swift GRB 170728B (Cenko et al., GCN 21371) 
with Zeiss-1000 of SAO RAS (July 29, August 4,5 ), AS-32 telescope of AbAO 
(July 29) and  Zeiss-1000  telescope of Tien Shan Astronomical Observatory 
(July  30,31 August 1,6).  Below we report the photometry of the optical 
afterglow (D'Avanzo et al., GCNs 21372, 21373; Heintz  et al., GCN 21374; 
Guidorzi   et al., GCN 21375) and upper limits of our observations. 
Preliminary photometry is following:

Date       UT start   t-T0    Filter Exp. OT     Err. UL  Telescope
                       (mid, days)     (s)             (3 sigma)

2017-07-29 00:41:51  0.07228  R    600   n/d     n/d  18.6  Z-1000 SAO
2017-07-29 17:27:49  0.79594 CR   43*60  n/d     n/d  20.4  AS-32  AbAO
2017-07-30 16:12:56  1.79815  R  97*120   21.93  0.25  22.1  Z-1000 TSHAO
2017-08-01 15:12:51  3.72304  R  60*120  n/d     n/d  21.6  Z-1000 TSHAO
2017-08-04 00:41:51  5.98081  R  41*300   22.6  0.23  22.8  Z-1000 SAO

The photometry is based on nearby USNO-B1.0 stars

1601-0108291 15:52:31.54 +70:09:31.7 R2 17.95

1601-0108289 15:52:28.99 +70:09:26.3 R2 18.08

1601-0108260 15:51:57.87 +70:09:53.8 R2 16.87

1601-0108254 15:51:50.88 +70:08:41.2 R2 15.04

1601-0108262 15:52:03.24 +70:07:32.0 R2 16.01

Coordinates of the afterglow obtained from observation on July 30 are 
(J2000)
15 51 55.5179 +70 07 21.123  with uncertainties on both coordinates of  0.2 
arces which is compatible with coordinates of TNG (D'Avanzo et al., GCN 
21373) and VLA (Fong  et al., GCN 21395). The  finding chart can be found in
http://grb.rssi.ru/GRB170728B/GRB170728B_TShAO_R_170730.png

The light curve of the afterglow based on  observations above and photometry 
reported in GCNs (Dintinjana et al., GCN 21394; Watson GCN 21389;   D'Avanzo 
et al., GCN 21372; Heintz  et al., GCN 21374; Guidorzi   et al., GCN 21375) 
can be found in
http://grb.rssi.ru/GRB170728B/GRB170728B_lc+GCNs_v2.png
Based on our observation on July, 30 (~ 1.8 days after burst onset) one can 
suggest that the OT experienced  rebrightening at that epoch.