[vsnet-grb-info 7772] GRB 090323: optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9324
SUBJECT: GRB 090323: optical observations
DATE:    09/05/05 00:46:36 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

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

We observed the afterglow (Updike et al., GCN 9026; Cenko et al., GCN 9027) 
of Fermi GRB 090323 (GBM trigger 259459364 / 090323002; Ohno et al., GCN 
9021)  on Apr. 28 and Apr. 29 with Shajn telescope of CrAO.  We  clearly 
detect the afterglow in R and do not detect in I- filter. Astrometry of the 
afterglow is RA(J2000):  12 42 50.29 Dec(J2000): +17 03 11.98 with 
uncertainty of 0.2 arcsec is compatible with reported in GCN 9026.

A photometry of combined images based on  USNO-B1.0  star  RA=12:42:39.3 
Dec=+17:05:05.7  (previously used by Kann et al. GCN 9033)   is following:

T0+     Filter, Exposure, mag.,  err.  Seeing
(d)             (s)

5.9934 R  91x60  22.7 +/- 0.1        1.6"
6.8990 I  84x60  >22.4  (3sigma)   2.9"

The combined image of the observation on Apr. 28 can be found at 
http://grb.rssi.ru/GRB090323/GRB090323_R_ZTSh_090328.gif

Our photometry in R is compatible with estimations obtained in nearby epochs 
(Kann et al. GCN 9041, de Ugarte Postigo et al. GCN 9051) and confirms the 
flattening of the light curve mentioned by de Ugarte Postigo et al. (GCN 
9051).  The non-detection of the afterglow in I-filter in  second epoch of 
our  observation  (T0+6.899 d) tentatively supports the steepening of light 
curve discussed by Kann et al. (GCN 9063). Indeed the upper limit I > 22.4 
is translating into R > 22.8 provided the color index R-I ~ 0.4 obtained 
from observations of Updike et al. (GCN 9026) and  Guidorzi et al. (GCN 
9039) is not changing along  late time light curve.