GCN Circular 21386

GRB 170728A: Swift/UVOT Detection

S. J. Laporte (PSU) and J. K. Cannizzo (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170728A
74 s after the BAT trigger (Cannizzo et al., GCN Circ. 21367
Not found
 
 
).
A fading source consistent with the XRT position
(Goad et al. GCN Circ. 21368
Not found
 
 
)
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  03:55:33.17 =  58.88819 (deg.)
    Dec (J2000) = +12:10:54.7  =  12.18187 (deg.)
with an estimated uncertainty of 0.56 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             70            219          147         19.20+-0.17   
white             70           4048          342         19.93+-0.18
v                 4264         5808          267        >19.1
b                 3655        11916          345        >19.7
u                  287        22167         1283        >20.0
w1                6020        21852         1105        >20.1
m2                5814        16112         1082        >20.6
w2                4059         4259          197        >19.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.24 in the direction of the burst
(Schlegel et al. 1998).