GCN Circular 10108
Subject
GRB091029: Swift/UVOT observations
Event
Date
2009-10-29T21:13:14Z (17 years ago)
From
Frank Marshall at GSFC <marshall@milkyway.gsfc.nasa.gov>
F. E. Marshall (GSFC) and D. Grupe (PSU) report on
behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 091029
91 sec. after the BAT trigger (Grupe et al., GCN Circ. 10097).
We detect the optical afterglow at the refined UVOT position
RA, Dec 60.17745, -55.95557, which is
RA (J2000) 04:00:42.59
Dec (J2000) -55:57:20.0
with an estimated uncertainty of 0.55 arcsec (radius, 90% confidence).
This position is consistent with the enhanced XRT position (Goad
et al., GCN 10102). The detection in the white, v, b and u filters and
not in the UV filters is consistent with the redshift
of 2.752 (Chornock et al., GCN 10053).
The afterglow brightened by a factor of 4 between the first two
observations in the white filter, which had mean observing times
of T+166 s. and T+594s. The afterglow then decayed following
an approximately power law form with a decay index of -0.45.
This decay form lasted until at least T+8231 s.
A similar optical light curve was reported by LaCluze et al.
(GCN Circ. 10099 and 10107).
Preliminary magnitudes and 3 sigma upper limits are reported below.
Filter T_start(s) T_stop(s) Exposure(s) Mag Err
------------------------------------------------------------------------
white 91 240 147 20.22 +/- 0.13
white 584 603 19 18.75 +/- 0.14
v 635 654 19 17.81 +/- 0.26
b 559 578 19 19.04 +/- 0.28
u 303 552 19 18.42 +/- 0.08
uvw1 684 1280 58 > 19.32
uvm2 1930 1949 19 > 18.74
uvw2 611 1206 58 > 20.45
-------------------------------------------------------------------------
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).