GCN Circular 18255

M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150907A
8821 s after the MAXI trigger (Suzuki et al., GCN Circ. 18246
Not found
 
 
).

No optical source consistent with the XRT Source 1 position given in
Kennea et al. (GCN Circ. 18250
Not found
 
 
) is detected in the summed u band exposures.

We note however, that there is source in the DSS catalogue consistent
with the XRT Source 1 position.


Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the exposure
for source 1 is:

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

u                8821        18835         336           >19.5


The magnitudes in the table are not corrected for the Galactic 
extinction due
to the reddening of E(B-V) = 0.08 in the direction of the burst 
(Schlegel et al. 1998).

-- 

Dr. Massimiliano De Pasquale
Research associate - Swift UVOT scientist
Mullard Space Science Laboratory, University College London