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GCN Circular 23205

Subject
GRB 180904A: Swift/UVOT Upper Limits
Date
2018-09-05T15:58:34Z (6 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180904A
131 s after the BAT trigger (D'Ai et al., GCN Circ. 23194).
No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23196)
is detected in the initial UVOT exposures, consistent with the non-detections
of Malesani et al. (GCN Circ. 23195), Izzy et al. (GCN Circ 23197), 
Moskvitin et al. (GCN Circ. 23198) and Guidorzi et al. (GCN Circ. 23199).
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC           131          281          147         >21.1
u_FC               289          539          246         >20.1
white              131          589          167         >21.1
v                  620          640           19         >20.1
b                  545          565           19         >19.4
u                  289          539          246         >20.1
w1                 670          690           19         >18.1
w2                 595          615           19         >18.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).
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