GCN Circular 21188
Subject
GRB 170531B: Swift/UVOT Detection
Event
Date
2017-06-02T04:27:30Z (9 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 170531B
152 s after the BAT trigger (Evans et al., GCN Circ. 21171).
We detect a possible afterglow consistent with the position given by GTC
(de Ugarte Postigo et al., GCN Circ. 21177) and MASTER (Tyurin et al.,
GCN CIrc. 21179).
The preliminary UVOT position is:
RA (J2000) = 19:07:32.10 = 286.88373 (deg.)
Dec (J2000) = -16:25:05.8 = -16.41829 (deg.)
with an estimated uncertainty of 0.1 arc sec. (radius, 90% confidence).
This position is 3.0 arc sec away from the enhanced XRT position
(Osborne et al. GCN Circ. 21175). Given the fading, detection
by other observatories and lack of matching source in the DSS, we find it
likely to be the GRB afterglow.
Preliminary 3-sigma magnitudes 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) 152 302 147 20.50+-0.29
white 590 1532 244 >21.03
v 640 1581 116 >18.88
b 566 1508 97 >19.77
u (fc) 310 560 245 >20.07
u 713 1643 85 >19.17
uvw1 689 1630 97 >18.91
uvm2 664 1606 116 >18.88
uvw2 615 1557 116 >19.14
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.19 in the direction of the burst
(Schlegel et al. 1998).