[vsnet-grb-info 8400] GRB 090915: Swift/UVOT detection of an optical afterglow candidate
GCN Circulars
gcncirc at capella.gsfc.nasa.gov
Thu Sep 17 07:01:30 JST 2009
TITLE: GCN CIRCULAR
NUMBER: 9918
SUBJECT: GRB 090915: Swift/UVOT detection of an optical afterglow candidate
DATE: 09/09/16 22:01:24 GMT
FROM: Erik Hoversten at Swift/Penn State <hoversten at astro.psu.edu>
E. A. Hoversten (PSU) and T. Sakamoto (NASA/UMBC) report on behalf of
the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 090915
44647 s after the BAT trigger (Cummings & Markwardt, GCN Circ. 9912).
A faint source is detected with 5.6-sigma confidence in the summed
UVOT observations at the position RA, Dec (J2000) = 238.02016,15.48772
which is equivalent to:
RA (J2000) = 15:52:04.84
Dec (J2000) = 15:29:15.8
with an estimated uncertainty of 0.8 arcsec (radius, 90% confidence).
This position is 0.2 arcsec from the UVOT-enhanced XRT position
(Beardmore, et al. GCN Circ. 9914) and the two positions agree within
the error bars. It is unclear at this point if the source is fading,
but follow-up Swift observations are being planned.
The observed magnitudes using the UVOT photometric system (Poole et
al. 2008, MNRAS, 383, 627) for the initial exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
=======================================================================
white 45492 52117 1647 22.15 +/- 0.24 (4.7 sigma)
v 46338 52837 1583 21.08 +/- 0.39 (2.8 sigma)
u 44647 51275 1647 21.40 +/- 0.43 (2.5 sigma)
The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).
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