GCN Circular 16676

NPM Kuin (UCL/MSSL), K.L.Page (U. Leicester) and F. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of Fermi Trigger
429246673 (GRB 140809A) as follow-up on the GRB candidate reported
detected by MASTER (Shumkov et al. (ATEL 6379) and confirmed by Masi
(GCN Circ. No 16675).  Swift observations started on  2014-08-10T00:55,
77.2 ks after the Fermi trigger.

We have analysed 2.0 ks of XRT data collected between 77.2-79.2 ks after
the trigger. No X-ray source was found, to an upper  limit of 4.0x10^-3
count s^-1 (3-sigma; 0.3-10 keV).

The UVOT observed the candidate field taking three v-band, one uvm2 and
one uvw2 exposure. The new source is found at the edge of a galaxy
(CG +11-15-003 at z=0.041372) and is only seen in the v-band, while the
uv bands appear dominated by galaxy emission. The source position is
consistent with that reported by Masi (GCN CIRC. No 16675).

Preliminary 3-sigma upper limits 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

 v            78122        79027          885         17.27 +/- 0.05
 m2           79032        79208          174         18.78 +/- 0.26
 w2           77214        78114          886         18.74 +/- 0.11

Times given relative to 2014-08-09T03:11:10.2.
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).

The source brightness remains close to the unfiltered magnitude reported by
MASTER, and has no X-ray counterpart.  Is therefore unlikely to be a GRB.