[vsnet-grb-info 16445] GRB150418A: Swift/UVOT did not detect a new source

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17726
SUBJECT: GRB150418A: Swift/UVOT did not detect a new source
DATE:    15/04/21 23:05:38 GMT
FROM:    Paul Kuin at MSSL  <npkuin at gmail.com>

N.P.M. Kuin (UCL/MSSL) reports on behalf of the Swift UVOT team:

Swift UVOT observations were made concurrently with the XRT observations
reported by  Sbarufatti et al. (GCN Circ. 17722 and 17725) of
GRB 150418A which was discovered by MAXI (Serino et al., GCN Circ.
No. 17719). At the location of the possible X-ray source detections
named source 1 and source 2 no new source was detected in the
u-band, with the following limits:

Source 1: u > 22.9 at 72.2 ks since the MAXI trigger at
    2015-04-18T00:52:08UT for an exposure time of 3.9ks
Source 2: u > 21.17 at t = 19ks since the MAXI trigger,
    for an exposure time of 322s.

However, we note that source 1 is at a distance of 4.6 arcsec of
a known nearby source in GSC2.3 (designated S5FU004949). That
source was detected with a magnitude u=20.38 +/- 0.15.

No correction was made for the galactic reddening
of E(B-V) = 0.043 and 0.373 respectively (Schlafly & Finkbeiner
2011 (ApJ 737, 103) ) at the locations of the sources 1 and 2.