GCN Circular 18922

S. R. Oates (IAA-CSIC/UCL-MSSL) and L. M. Z. Hagen (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160121A
152 s after the BAT trigger (Hagen et al., GCN Circ. 18912
Not found
 
 
).
No optical afterglow consistent with the optical position
reported by MOA (Oates et al., GCN Circ. 18917
Not found
 
 
) 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

u_FC               152          401          246         >19.7
v                  435          830           78         >18.6
u                  152          918          356         >19.9
w1                 484          754           58         >18.3
m2                 459          854           78         >18.4
w2                 410          805           78         >18.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.53 in the direction of the burst
(Schlafly and Finkbeiner 2011).