{
  "bibcode": "2002GCN..1556....1G",
  "body": "A. Gal-Yam (Tel Aviv University) reports:\n\n\"We have extracted from the USNO plate archive\n(http://ftp.nofs.navy.mil/data/fchpix/) two blue plates, covering the\nlocation of the variable object possibly connected with XRF 020903,\nreported by Soderberg et al (GCN 1554). Inspecting these plates we find\nthe following:\n\n1) A plate obtained on UT 1977.6 reveals an object, coincident with the\nvariable source reported by Soderberg et al. The B-band magnitude of this\nobject appears to be about one magnitude fainter than that of the nearby\ngalaxy noted as \"G2\" by these authors.\n\n2) Comparison of the 1977 plate with the (much poorer) POSSI blue plate\nobtained on 1954.6 may suggest a variation of the flux ratio between the\nsource coincident with the Soderberg et al. variable, and the galaxy G2,\nwith G2 being brighter on the 1977 plate, but possibly fainter than the\nsource reported by Soderberg et al., in 1954. This may hint that this\nsource was variable in the past. We stress, however, that the 1954 data\nare quite poor, so past variability can not be ascertained at this stage.\n\nGIF Cutouts from both plates, showing the area around the Soderberg et al.\nvariable, can be obtained from ftp://wise3.tau.ac.il/pub/avishay/xrf.\nThese can be compared with the Palomar data shown by Soderberg at\nhttp://www.astro.caltech.edu/~ams/XrF.html.\n\nThe source detected on the 1977 plate may be hard to interpret as a\npossible \"host\" galaxy for the Soderberg et al. transient, even if we\ndisregard its possible past variability. Soderberg et al. report that this\nsource is not detected on POSSII red plates, and estimate a magnitude of\nR=22 from their OT+SN+host model. This fact can be reconciled with the\n1977 B-band data, showing this object only about 1 magnitude fainter than\nG2 (which has R=17 mag), if this object has a very blue B-R color.\nHowever, this appears to be in contradiction with the Magellan spectrum\npresented by Soderberg et al., which is flat, or possibly even red, in\nB-R.\n\nAn alternative explanation fitting both the archival analysis and the\nentire data set presented by Soderberg et al. and Berger et al (GCN 1555)\nis that this source is a variable radio-loud AGN. We have recently shown\n(Gal-Yam et al. 2002, PASP, 114, 587) that such objects can appear to be\nvery similar to optical transients associated with GRBs. Further\ninspection of archival data, as well as further observations (B-band\nespecially), can distinguish between an OT+SN model, and an AGN, according\nto their variability properties.\n\nIf an AGN, the source discovered by Soderberg et al. may still be related\nto XRF 020903. However, in that case, a SN component no longer seems to be\nrequired.\n\nUntil this issue is clarified, we urge some caution in interpreting the\nSoderberg et al. data set as evidence for a connection between XRF 020903\nand a SN.\n\nThis work has made use of the USNOFS Image and Catalogue Archive operated\nby the United States Naval Observatory, Flagstaff Station\n(http://www.nofs.navy.mil/data/fchpix/).\"",
  "circularId": 1556,
  "createdOn": 1033328764000,
  "email": "ejb@astro.caltech.edu",
  "subject": "XRF 020903: Archival Optical Images",
  "submitter": "Edo Berger at Caltech  <ejb@astro.caltech.edu>"
}