[vsnet-grb-info 12643] GRB 121123A: Swift/UVOT Observations
GCN Circulars
gcncirc at capella2.gsfc.nasa.gov
Tue Nov 27 07:25:17 JST 2012
TITLE: GCN CIRCULAR
NUMBER: 14003
SUBJECT: GRB 121123A: Swift/UVOT Observations
DATE: 12/11/26 22:25:09 GMT
FROM: Stephen Holland at STScI <sholland at stsci.edu>
S. T. Holland (STScI) and
E. A. Helder (PSU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB
121123A starting 131 s after the BAT trigger (Helder et al., 2012,
GCNC 13982). The refined UVOT position is
RA (J2000) 20:29:16.30 = 307.31792 (deg)
Dec (J2000) -11:51:35.6 = -11.85989 (deg)
with an estimated uncertainty of 0.44 arcsec (radius, 90% confidence,
statistical + systematic). We observe a slow decay of the optical
afterglow, consistent with that reported by Xu et al., (2012, GCNC
13986). The afterglow is weakly detected in white at approximately 40
ks after the BAT trigger. However, the UVOT photometry is affected by
a bright (B ~ 14 mag) star (USNO B1.0 0781-0714667) located
approximately 22 arcsec north of the afterglow, so the late-time
behavior of the optical afterglow's light curve requires further
analysis. Preliminary UVOT photometry, and 3-sigma upper limits, for
the afterglow are presented below.
------------------------------------------------------
Filter TSTART TSTOP Exposure Mag Err
------------------------------------------------------
white (fc) 131 281 147 19.43 0.15
u (fc) 289 539 246 19.35 0.23
white (fc) 869 1019 147 19.13 0.12
------------------------------------------------------
v 619 1070 58 18.29 0.33
b 546 1169 58 19.12 0.29
u 695 1145 39 18.58 0.32
uvw1 669 18,011 2137 >21.5
uvm2 645 17,104 1376 >21.3
uvw2 595 22,980 1376 >21.5
white 570 590 19 >19.7
------------------------------------------------------
The detection in the UVOT u band, combined with the non-detection
in the UVOT uvw1 band, is consistent with GRB 121123A having a
redshift of approximately 1.5 < z < 3.4.
The quoted magnitudes and upper limits have not been corrected for
the Galactic extinction along the line of sight to this burst of
E_{B-V} = 0.05 mag (Schlafly et al. 2011, ApJS, 737, 103). The
photometry is in the UVOT photometric system (Breeveld et al. 2011,
AIP Conf. Proc. 1358, 373).
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