GCN Circular 17977

Paul Kuin (MSSL-UCL), Marissa McCauley (PSU) and Daniele Malesani 
(DARK/NBI) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of the Fermi GRB 
150627A 33622 s after the LAT trigger (Arimoto et al., GCN Circ. 17971
Not found
 
 
; 
Yu et al., GCN Circ. 17975
Not found
 
 
).

An optical object consistent with the XRT position (Gompertz et al., GCN 
Circ. 17976
Not found
 
 
) is detected at RA, Dec = 117.47108, -51.489417 deg (J2000), 
which is equivalent to:

RA (J2000):  07:49:53.06
Dec(J2000): -51:29:21.9

with an uncertainty of 1".

Preliminary detections using the UVOT photometric system (Breeveld et 
al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:

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

white         33963          34289         335     19.11+/-0.10
white         39860          40112         248     19.55+/-0.17
white         45659          45863         204     19.28+/-0.14
v         34304          34601         298     19.02+/-0.32
v         40117          40346         225     18.98+/-0.36
u         33622          38243         577     18.90+/-0.10
u         43668          45654         966     19.00+/-0.11

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.32 in the direction of the 
burst (Schlegel et al. 1998).

While no optical variability can be securely inferred from the UVOT 
photometry, the source is not visible in the DSS survey, and brighter 
than its limit, which suggests it to be the optical afterglow of GRB 
150627A.