TITLE:   GCN CIRCULAR
NUMBER:  15358
SUBJECT: GRB 131018A: Swift/UVOT Upper Limits
DATE:    13/10/19 17:28:41 GMT
FROM:    Massimiliano de Pasquale at MSSL-UCL  <m.depasquale@ucl.ac.uk>

M. De Pasquale (UCL-MSSL) and A. Melandri (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 131018A
99 s after the BAT trigger (Melandri et al., GCN Circ. 15349).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 15352) is detected in the initial UVOT exposures.
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           120          270          147         >21.3
u_FC               279          528          246         >20.5
white              120        13702         1588         >22.4
v                   99         7600          581         >20.3
b                  534        19468         2174         >22.0
u                  279        18703         2368         >21.9
w1                 657        17790         1382         >21.3
m2                 632         7805          568         >20.5
w2                 584         7395          568         >20.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.26 in the direction of the burst
(Schlegel et al. 1998).