GCN Circular 22357

F. E. Marshall (NASA/GSFC) and J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift/UVOT team:

Additional observations of the optical afterglow of GRB 180115A
discovered with Swift/UVOT (Cannizzo et al., GCN Circ. 22335
Not found
 
 
)
reveal an initially brightening and then fading source.
The source is not detected in any of the UV filters, consistent
with the redshift of 2.487 reported by de Ugarte Postigo et al. (GCN Circ. 22346
Not found
 
 
).

The preliminary UVOT position is:
    RA  (J2000) =  00:48:09.27 =  12.03862 (deg.)
    Dec (J2000) = -15:37:49.9  = -15.63054 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

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

white              140          290          147         17.61 +/- 0.04
white              753          773           20         16.95 +/- 0.07
white             5663         5863          197         19.18 +/- 0.08
v                  628          648           20         16.50 +/- 0.16
b                  554          574           20         16.93 +/- 0.11
u                  299          548          246         16.32 +/- 0.04
w1                1109        13068         1165        >20.7
m2                4743        12296         1279        >21.8
w2                5769         7329          318        >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).