TITLE:   GCN CIRCULAR
NUMBER:  9179
SUBJECT: GRB 090418A: optical observations
DATE:    09/04/20 22:23:53 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

E. Pavlenko, V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:

We observed the error box of  Swift GRB 090418A in   series of BVRI
exposures on Apr. 18 with Shajn telescope of CrAO.  We  detect the afterglow
(Chornock et al., GCN 9148, Mangano et al., GCN 9149) in all filters in
stacked images. Astrometry of the afterglow is RA(J2000):  17 57 15.17
Dec(J2000): +33 24 21.14 with uncertainty of 0.3 arcsec is fully compatible
with reported one in GCNs 9148, 9149.

Preliminary photometry of combined images is based on  USNO-B1.0
1234-0288651 star  RA=17:57:13.29 Dec=+33:25:00.6   is following:


T0+     Filter, Exposure, mag.,     err.
(d)             (s)
0.5484   B       36x60     23.30  +/- 0.20
0.5484   R       17x60     22.23 +/- 0.14
0.5491   I        17x60     22.40  +/- 0.24

We note, that OT is ~4" North-West of bright galaxy which is also  visible 
in POSS2.
Taking the redshift z=1.608 of the GRB source (Chornock et al., GCN  9151)
and the scale of  ~8.6 kpc/" at that redshift it is unlikely that the galaxy 
is related with OT.

A finding chart the combined image in I can be found at
http://grb.rssi.ru/GRB090418A/GRB090418_I_ZTSh_090418.gif