GCN Circular 17531

M. M. Chester (PSU) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150301B
86 s after the BAT trigger (Lien et al., GCN Circ. 17515
Not found
 
 
).  A fading 
source consistent with the XRT position (Evans et al. GCN Circ. 17520
Not found
 
 
) 
and the optical transient reported by Buckley et al. (GCN Circ. 17518
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  05:56:39.89 =  89.16622 (deg.)
   Dec (J2000) = -57:58:10.4  = -57.96955 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits for the White finding 
chart and subsequent exposures 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_FC            86          236          147         16.2 +/- 0.1
white             3986         4121          133        >20.2
v                 5833         6033          197        >19.7
b                 3782         3982          197        >19.6
u                  298          543          241         17.1 +/- 0.1
w1                6243        10068          579        >19.9
m2                6038         6237          197        >19.8
w2                5628        16054          963        >21.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.08 in the direction of the burst
(Schlegel et al. 1998).