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GCN Circular 20574

Subject
GRB 170131A: Swift/UVOT Upper Limits
Date
2017-02-02T14:21:17Z (7 years ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
A. A. Breeveld (UCL-MSSL), M. Stamatikos (OSU) and F. E. Marshall 
(NASA/GSFC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170131A 
78368 s after the BAT trigger (Palmer, GCN Circ. 20570) using the UVW2 
filter only.
No optical afterglow consistent with the XRT source 1 position (Melandri 
et al., GCN Circ. 20573) is detected in the initial UVOT exposures. 
However, there is a USNO-B1.0 source at this position (USNO-B1.0 
1540-029147), but it is not detected in the UVW2 filter.
The preliminary 3-sigma upper limit using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial 
exposures is:

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

w2               78368        96539         4888         >21.2

The magnitude in the table is not corrected for the large, but uncertain 
Galactic extinction due to the reddening of E(B-V) = 1.19 in the 
direction of the burst (Schlegel et al. 1998).
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