TITLE:   GCN CIRCULAR
NUMBER:  21000
SUBJECT: GRB170405A, Swift-UVOT Detection
DATE:    17/04/07 06:46:05 GMT
FROM:    Sam LaPorte at PSU  <sjl5346@psu.edu>

GRB 170405A: Swift/UVOT Detection

S. J. LaPorte (PSU) and E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170405A
129 s after the BAT trigger (Troja et al., GCN Circ. 20984).  Consistent
with previous reports (Malesani et al, GCN Circ. 20988; Martin-Carrillo et al.
GCN Circ. 20991), a fading source consistent with the XRT position
(Evans et al. GCN Circ. 20985) is detected in the initial UVOT exposures at: 

    RA  (J2000) =  14:39:18.73 = 219.82805 (deg.)
    Dec (J2000) = -25:14:35.4  = -25.24317 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

The upper limits in the UV bands are consistent with the reported
redshift of z = 3.51 (de Ugarte-Postigo et al, GCN Circ. 20990).

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 (fc)         129          279          147         16.01 +/- 0.03
white              747          998          143         18.09 +/- 0.07
v                  618          637           20         16.31 +/- 0.14
b                  543          563           20         17.34 +/- 0.13
u                  287          711          265        >20.2
uvw1               667          859           39        >18.9
uvm2               815          835           19        >17.5
uvw2               593          786           39        >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.09 in the direction of the burst
(Schlegel et al. 1998).