{
  "bibcode": "2013GCN.15325....1X",
  "body": "D. Xu, D. Malesani (DARK/NBI), T. Kruehler (ESO), J.P.U. Fynbo\n(DARK/NBI), P. Jakobsson (U. Iceland) and John Telting (NOT) report on\nbehalf of a larger collaboration:\n\nWe observed the location of the candidate optical afterglow\n(iPTF13dsw; Kasliwal et al., GCN 15324) of the Fermi-GBM trigger\n403206457\nwith the NOT telescope equipped with ALFOSC. We obtained two R-band\nimages with an exposure time of 300 s each starting at 01:32 UT\n2013-10-13 in a good seeing of ~0.65\".\n\nThe candidate afterglow is clearly detected in each image as a\npoint-like source, and we measure an R-band magnitude of R = 21.6 mag\nassuming R = 18.36 mag for the nearby star at RA = 02:10:07.95, Dec =\n-04:24:41.7 at a midpoint of 01:35 UT.\n\nAccounting for the different calibration system with respect to the\nmagnitudes given in Kasliwal et al. (GCN 15324), the source has faded\nby approximately 1.6 magnitudes with respect to the earlier P60 measurement.\n\nUnder the assumption that the transient decays as a single power-law,\nthis fading corresponds to a decay index of ~1.6, not untypical of GRB\nafterglows at the given epoch.\n\nWe thank S. B. Cenko for private information about the photometric\ncalibration of the P60 measurement.",
  "circularId": 15325,
  "createdOn": 1381641709000,
  "email": "dong.dark@gmail.com",
  "subject": "Fermi403206457: NOT optical observations",
  "submitter": "Dong Xu at DARK/NBI  <dong.dark@gmail.com>"
}