TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2631 SUBJECT: XRF 040701 - optical observations of the decaying Chandra source DATE: 04/07/23 05:15:04 GMT FROM: 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."