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GCN Circular 2631

XRF 040701 - optical observations of the decaying Chandra source
2004-07-23T05:15:04Z (20 years ago)
Derek Fox at CIT <>
E. Berger (Caltech/Carnegie), A. Gal-Yam, D.B. Fox (Caltech), I.
Thompson (Carnegie), B. Schmidt, R. McNaught and B. Peterson (MSO,ANU)
report on behalf of a larger collaboration:

"We used the Du Pont 2.5-m Telescope + CCD at the Las Campanas
Observatory on July 16.29, 17.29, 18.28 and 19.25 UT to image an 8.8'
x 8.8' field centered on the position of Chandra X-ray source CXO-2
(GCN 2626) -- suggested by Fox (GCN 2630) as a possible counterpart of
XRF 040701 (GCN 2620) and associated with a galaxy at a redshift
z=0.2146 (GCN 2627).  All observations were performed in the R band in
good seeing and weather conditions with exposure times of 20 minutes
on the first three nights and 25 minutes on July 19.  In addition, we
obtained an R-band image of the field with the 40-in telescope at
Siding Springs Observatory on July 14.

Using PSF-matched image subtraction (with the CPM/DDA algorithm, as in
Gal-Yam et al. 2004, ApJ, 609, L59), we detect no sign of
variability. If this is in fact the counterpart of XRF 040701, and
assuming that any optical emission during this period would be
dominated by a SN 1998bw-like event, associated with this XRF, then
the lack of variability may not be surprising. Owing to its broad
peak, SN 1998bw varied by only 0.1 mag in the rest-frame V-band during
the same time.  It is also possible that a SN associated with XRF
040701 is extinguished by dust and/or is fainter than SN1998bw."
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