TITLE:   GCN CIRCULAR
NUMBER:  42354
SUBJECT: GRB 251016A: Swift/UVOT Detection
DATE:    25/10/18 12:05:09 GMT
FROM:    s.shilling@lancaster.ac.uk

S.P.R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251016A,
detected by SVOM/ECLAIRs (Basa et al., GCN Circ. 42308) and Fermi/GBM
(Fermi GBM team, GCN Circ. 42309), 6.66 ks after the SVOM/ECLAIRs trigger.

A source is detected in the optical by the Swift/UVOT at a position that is
consistent with the likely X-ray counterpart detected by the Swift/XRT
(Source 1: Evans et al., GCN Circ. 42311). 

Preliminary detections and upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the images are:

Filter         T_start(ks)   T_stop(ks)      Exp(s)            Mag

u	       6.66	     12.6	     491.7	       19.13 +/- 0.26
b	       6.91	     12.7	     296.0	       18.70 +/- 0.18
v	       7.42	     7.67	     245.8	       17.52 +/- 0.15
w1	       12.1	     12.4	     245.8	       >18.93
w2	       7.17	     7.42	     245.8	       >19.05
m2	       7.68	     7.85	     168.3	       >18.66

The magnitudes reported here are not corrected for Galactic extinction.