TITLE:   GCN CIRCULAR
NUMBER:  15894
SUBJECT: GRB 140226A/iPTF14yb: Swift/UVOT Observations
DATE:    14/02/28 16:39:17 GMT
FROM:    Mike Siegel at PSU/Swift MOC  <siegel@swift.psu.edu>

M. H. Siegel (PSU), F. E. Marshall (NASA/GSFC) and A. P. Beardmore (U. Leicester)
report on behalf of the Swift/UVOT team:

Swift/UVOT started observations of GRB140226A/iPTF14yb (Cenko et al., GCN Circ. 
15833) 25718 s after the IPN trigger (Hurley et al., GCN Circ. 15888).
No optical counterpart is detected at the position of the iPTF or
XRT positions (Beardmore et al., GCN Circ 15884) in summed
exposures.

Preliminary 3-sigma upper limit using the UVOT photometric system 
(Breeveld et al al. 2011, AIP Conf. Proc. 1358, 373) is:

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

uvm2      25718        43672      2180     >21.24
v        124093       136265      4877     >20.96
v        147705       154552      1822     >20.54

No correction has been made for the expected Galactic extinction 
corresponding to E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).