TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1561 SUBJECT: XRF 020903: Correction to GCN 1560 DATE: 02/09/30 21:32:57 GMT FROM: Daniele Malesani at Brera Astro. Obs. M. Stefanon, S. Covino, D. Malesani (INAF, Merate Obs., Milan, I), N. Masetti (IASF/CNR, Bologna, I.), G. Temporin (Inst. fur Astr. Innsbruck, A), and S. Desidera (Padova Astr. Obs., I), on behalf of a larger Italian collaboration, communicate: We have found that the star named (2) in our previous circular (GCN 1560) was actually saturated in our images. We hence removed it from our analysis. Here is the whole correct text. We observed the variable source in the field of XRF 020903 (Ricker et al., GCN 1530; Soderberg et al, GCN 1554) on 29.9 UT, with the 182cm telescope at Cima Ekar-Asiago, near Padova (Italy). The object was at high airmass. We find the following magnitudes for the suspect afterglow (AG) with respect to the USNO star (1) reported in the finding chart of Soderberg et al. (see http://www.astro.caltech.edu/~ams/XrF.html ): Filter UT Exposure AG - (1) ------------------------------------ V 29.923 600 sec 4.20+-0.09 R 29.931 600 sec 2.63+-0.01 I 29.937 300 sec 4.50+-0.13 In the I-band image, the object is barely visible. Using the USNO R-magnitude for the reference star (1), R = 16.0 (star 2 is saturated), we find R = 18.63 +- 0.2 @29.931 UT (26.5 days after XRF), where the error is mainly due to calibration. More accurate photometry will be distributed when available. Our data suggest further brightening between 28.3 and 29.9 UT, with respect to the value found in Soderberg et al. web page. With present data, we cannot say if the varying source is a rising supernova or a variable radio-loud AGN, as suggested by Gal-Yam (GCN 1556). Further observations are planned tonight. This message may be cited.