[vsnet-grb-info 9299] GRB 100418A: CrAO optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10783
SUBJECT: GRB 100418A: CrAO optical observations
DATE:    10/05/19 19:25:13 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 field of the Swift GRB 100418A (Marshall  et al. GCN 10612) 
with Shajn telescope of  CrAO between (UT) May, 14  21:07 -- 22:48 under 
photometric weather conditions and mean seeing of about 2 arcsec.
The preliminary photometry of the afterglow+host in a stacked image based on 
USNO-B1.0 star 1014-0271368  (RA(J2000) = 17:05:26.42 Dec(J2000)= 
+11:27:32.9)  assuming  R=17.32  is following:

T0+      Filter,   Exposure,  mag.
(mid, d)              (s)

26.0332     R       90x60    21.86 +/-0.06

The photometry is compatible with R-magnitude reported by Perley et al, GCN 
10727 (R=21.85+/-0.05 at 17.739 days) and still brighter than assumed 
R-magnitude of the normal type of host galaxy (SDSS based ugriz-> R 
conversion) which cannot be explained solely by afterglow contribution 
fading steeper than power law with decay index of  .~0.8.