[vsnet-grb-info 7680] Swift/UVOT observations of GRB 090424

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9234
SUBJECT: Swift/UVOT observations of GRB 090424
DATE:    09/04/24 21:42:37 GMT
FROM:    Samantha Oates at MSSL  <sro at mssl.ucl.ac.uk>

P.Schady (MSSL/UCL) and J. K. Cannizzo (NASA/UMBC) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT started settled observations of the burst GRB090424 
(Cannizzo et al. GCN Circ. 9223) with the finding chart (fc) exposure in 
white, 167s after the BAT trigger. The afterglow is detected in the all 
filters at the position reported by Cannizzo et al. (GCN Circ. 9223), 
placing an upper limit on the redshift of ~1.3.  The combined UVOT data 
indicates that the afterglow is fading with a decay index of alpha ~ 0.9.

The UVOT magnitudes our reported below:

Filter    Tmid(s)   Exp(s)   Magnitude
white (fc) 167        147.4   15.27 +/- 0.01
u (fc)     429        245.8   16.40 +/- 0.03

white      594        19.4    16.99 +/- 0.07
v          644        19.5    16.86 +/- 0.19
b          570        19.5    17.27 +/- 0.13
u          1122       19.5    17.44 +/- 0.20
uvw1       695        19.5    16.81 +/- 0.19
uvm2       670        19.4    17.39 +/- 0.34
uvw2       793        19.4    17.51 +/- 0.27

The values quoted above are in the UVOT photometric system (Poole et al. 
2008, MNRAS, 383, 627) and are not corrected for the expected Galactic 
extinction corresponding to a reddening of E(B-V)=0.025 mag in the 
direction of the burst (Schlegel et al. 1998).