GCN Circular 12642
Subject
GRB 111209A: Swift UVOT refined analysis
Date
2011-12-09T19:22:04Z (13 years ago)
From
Erik Hoversten at Swift/Penn State <hoversten@astro.psu.edu>
E. A. Hoversten (PSU) and M. H. Siegel (PSU), report on behalf of the
UVOT team:
The Swift/UVOT began settled observations of the field of GRB 111209A
427 s after the BAT trigger (Hoversten et al., GCN Circ. 12632). The
afterglow is clearly detected in all seven UVOT filters. We find a
refined UVOT position of
RA (J2000) 00:57:22.63 = 14.34429 (deg)
Dec (J2000) -46:48:03.8 = -46.80106 (deg)
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence,
statistical + systematic). This position is 0.25 arcseconds from the
UVOT-enhanced XRT position (Evans et al., GCN Circ. 12639), which is
within the errors.
The white, v, and b filters show a fading source over the first orbit,
however at the end of the first orbit the white magnitude increases
abruptly by 0.6 magnitudes corresponding with a significant flare in
the X-rays. The v, b, u, uvw1, and uvm2 magnitudes show a
rebrightening between 5.4 and 7 ks after the burst of 0.3 to 1.1
magnitudes. Preliminary magnitudes using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag Err
white_FC 427 577 147 17.94 0.04
white 855 1005 147 17.73 0.04
white 1856 1876 19 18.01 0.11
white 2030 2050 19 17.40 0.08
v 584 603 19 17.25 0.24
b 1134 1154 19 18.16 0.21
u 6064 6264 196 18.11 0.09
w1 633 653 19 17.16 0.24
m2 5653 5853 196 18.23 0.17
w2 5244 5443 196 17.96 0.12
The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.02 in the direction of
the burst (Schlegel et al. 1998).
The data from all three instrument is similar is several ways to GRB
060218, the long event associated with SN2006aj, and to GRB 101225A,
the Christmas burst. The detection in all UVOT filters implies a low
redshift of z < 1.6. We note that at 18 ks after the burst the source
is still at 18th magnitude in the white filter which is extremely
unusual. Given the rare behavior exhibited by GRB 111209A we advocate
for additional observations at all wavelengths.