[vsnet-grb-info 7711] GRB090426 Swift/UVOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9265
SUBJECT: GRB090426 Swift/UVOT observations
DATE:    09/04/26 22:13:22 GMT
FROM:    Samantha Oates at MSSL  <sro at mssl.ucl.ac.uk>

S. R. Oates (MSSL/UCL) and J. R. Cummings (NASA/UMBC) report on behalf of 
the
Swift/UVOT team:

The Swift/UVOT started settled observations of the burst GRB090426
(Cummings et al. GCN Circ. 9254) with the finding chart (fc) exposure in
white, 89s after the BAT trigger. The afterglow is detected in the white,
b, u and filters and marginally in the v filter at the refined UVOT 
position:

     RA (J2000)  12:36:18.07
    Dec (J2000)  32:59:09.6

with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
The lack of detection in the UV filters is consistent with a redshift
of 2.609, which was reported by Chornock et al. (GCN Circ. 9264).

The UVOT magnitudes and upper limits our reported below:

Filter    Tstart(s) Tstop(s)  Exp(s)       Magnitude/3sig UL
###################################################
white (fc)   89      239      147          17.52 +/- 0.03
u (fc)       301     551      246          18.11 +/- 0.08

white        581     600      19           19.10 +/- 0.22
v            630     650      19           19.04 +/- 0.86 (1.3-sigma)
u            556     576      19           18.59 +/- 0.38
b            706     726      19           18.92 +/- 0.36
uvw1         680     2164     175          > 19.92
uvm2         655     2139     175          > 19.63
uvw2         606     2090     136          > 19.82

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)=0.02 mag in the
direction of the burst (Schlegel et al. 1998).