GCN Circular 9076
Subject
Swift/UVOT observations of GRB090401B
Event
Date
2009-04-01T18:01:23Z (17 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and S.R.Oates (MSSL-UCL) reports on behalf of the
Swift/UVOT team:
Swift UVOT began settled exposures of GRB090401B (Schady et al, GCN 9066)
82 s after the burst trigger, and detected a bright optical transient at
the position reported in by Schady et al. (GCN 9067), consistent with the
enhanced XRT error circle (Osborne et al, GCN 9070).
The source is detected in the white, v, b and u filter, but not in any of
UV filters, placing an upper limit on the redshift of z < 3. We note that
the afterglow lies close to a known source, which may be contaminating our
phometry. The light curve decays steeply at early times at a rate of
alpha_1~1.5, and then breaks at ~T+440s to a slope of alpha_2~0.7.
Using 2.5arcsec aperture, the magnitudes and 3 sigma upper limits to our
observations our reported below:
Filt T_start (s) T_stop (s) Exp (s) Mag/3-sig UL
white 82 232 147 16.83+/-0.02
white 874 1024 147 19.14+/-0.08
v 623 1248 78 18.31+/-0.20
v 4753 4953 197 19.10+/-0.25
b 549 1346 58 19.48+/-0.26
b 5573 5773 197 20.39+/-0.28
u 293 543 246 17.99+/-0.07
u 698 1312 58 18.67+/-0.22
uvw1 672 1297 78 > 19.42
uvm2 647 1272 78 > 18.99
uvw2 599 1387 78 > 19.39
The above magnitudes have not been corrected for the Galactic extinction
corresponding to E(B-V) = 0.67 (Schlegel et al 1998). The photometry is on
the UVOT flight system described in Poole et al (2008, MNRAS, 383,627)