TITLE:   GCN CIRCULAR
NUMBER:  31422
SUBJECT: GRB 220107A: SAO RAS optical observations
DATE:    22/01/09 20:00:03 GMT
FROM:    Moskvitin Alexander at SAO RAS  <mosk@sao.ru>

A. Moskvitin (SAO), A. Medvedev (SAO), A. Pozanenko (IKI)
and N. Pankov (HSE) on behalf of larger GRB follow-up team report:

We observed the field of GRB 220107A (The Fermi GBM team, GCN 31399;
Kunzweiler et al. GCN 31400; DeLaunay et al. GCN 31402; Suresh et al.,
GCN 31408) with the SAO RAS 1-m telescope Zeiss-1000 + CCD-photometer
in BVRc bands on January 9.

The OT (Hosokawa et al. GCN 31413; Siegel GCN 31415; Zhu et al.
GCN 31416; Pankov et al., GCN 31419) is detected in stacked images
in each filter. Preliminary photometry of the afterglow is as follows.

UT start -- UT end    T_mid-T0, d  Filter Exp., s  mag +/- err

02:19:16 -- 03:00:13  1.4960       Rc     5 x 300  20.41 +/- 0.03
03:01:27 -- 03:18:33  1.5170       V      3 x 300  20.97 +/- 0.06
03:19:40 -- 03:36:26  1.5295       B      3 x 300  22.08 +/- 0.18

Photometry is based on nearby SDSS-DR12 stars
(magnitudes are converted with the Lupton 2005 transformations).

J2000.0 coordinates       B        V        R
11:19:13.93 +34:08:38.8   16.244   15.691   15.363
11:19:13.74 +34:11:49.6   18.811   17.880   17.327
11:19:12.27 +34:11:18.1   18.959   18.506   18.241