[vsnet-grb-info 20521] GRB 180402A: ISON-NM early optical limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22617
SUBJECT: GRB 180402A: ISON-NM early optical limits
DATE:    18/04/08 20:40:42 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

E. Mazaeva (IKI),  L. Elenin (KIAM),  A. Pozanenko (IKI), A. Volnova 
(IKI), I. Molotov (KIAM)  report on behalf of larger GRB  follow-up 
collaboration:

We observed the field of the Swift  short burst GRB 180402A (Lien et 
al., GCN 22580) with 0.4-m telescope of ISON-NM observatory starting on 
Apr., 02 (UT) 09:45:39, i.e. 40 seconds after the burst trigger. We 
obtained 4 unfiltered images of 30 s exposure each. We do not detect any 
source within XRT error circle (Lien et al., GCN 22580). Upper limits 
are following.

Date      start (Ut)   t-T0         Exp.     UL (3sigma)
                       (mid.,sec)    (s)
2018-04-02 09:45:39   55            1*30     14.5
2018-04-02 09:45:39  133            4*30     15.0

The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes).