GCN Circular 10054
Subject
GRB091020 Swift/UVOT observations
Date
2009-10-21T11:18:58Z (15 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL-UCL) and J. L. Racusin (NASA/GSFC/ORAU) report on
behalf of the Swift/UVOT team:
The Swift/UVOT began observerving the field of GRB 091020 89 s
after the BAT trigger (Racusin et al., GCN Circ. 10048). We detect the
optical afterglow in all filters at the refined UVOT position
RA, Dec 175.730, +50.97833, which is
RA (J2000) 11:42:55.20
Dec (J2000) 50:58:42.0
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
This position is consistent with the enhanced XRT position (Beardmore
et al., GCN 10050). The detection in the white, v, b and u filters and
the weak detection in the uvw1 filter is consistent with a redshift
z~1.7, which is consistent with redshift reported by NOT (Xu, et al.,
GCN 10053).
Preliminary magnitudes and 3 sigma upper limits are reported below.
Filter T_start(s) T_stop(s) Exposure(s) Mag Err
------------------------------------------------------------------------
white 89 239 147 15.73 +/- 0.01
white 874 1024 147 17.27 +/- 0.03
v 799 819 19 16.40 +/- 0.15
b 1153 1173 19 17.27 +/- 0.15
u 707 727 19 17.06 +/- 0.16
uvw1 683 6929 490 20.29 +/- 0.35
uvm2 657 6723 490 > 20.29
uvw2 608 6314 303 > 20.27
-------------------------------------------------------------------------
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.02 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383,627).