{
  "bibcode": "2003GCN..2236....1D",
  "body": "GRB 030418: Second Epoch Optical Observations with Magellan\n\nA. Dullighan, N. R. Butler, G. R. Ricker, J. L. Elliot, K. Clancy\n(MIT), and D. Osip (Las Campanas Observatory)\n\nreport:\n\nOn 2003 April 25.00 UT, we observed the optical afterglow (Price et \nal; GCN2148) of the HETE-localized GRB 030418 (Shirasaki et al; \nGCN2210) with the Magellan 6.5 meter Clay telescope at Las Campanas \nObservatory in Chile.  Our observations consisted of two 400s R-Band \nimages, one 400s I-Band image, and one 400s V-Band image taken with \nthe MagIC instrument.\n\nThe afterglow declined in brightness with respect to our previous \nmeasurements (Dullighan et al; GCN2168). The R band data is \nconsistent with a revised power law decay index = 1.2 +/- 0.1, when \nthe two data points from Price et al. (GCN2148 and GCN2150) are \nincluded.  The afterglow was still point-like, but very close to the \nlimiting magnitudes of the images.  No evidence of a host galaxy is \nobserved.  We can, however, place a limit on the redshift of the \nafterglow of z<~5, due to the small V-R color difference we observe \n(i.e., no evidence for a Lyman alpha break). Our second epoch results \nwere as follows:\n\nUT               t-t0 (days)   Mag\n2003-04-25.00    6.58          R=24.9 +/- 0.4\n2003-04-25.01    6.59          I>24 (limiting magnitude)\n2003-04-25.02    6.60          V=25.1 +/- 0.5\n\nThe magnitudes reported above are referenced to the photometry \nreported by A. Henden (GCN2216).  We have also recalibrated the \nmagnitudes we reported in GCN 2168 to A. Henden's photometry \n(GCN2216).  The errors in calculating relative magnitudes have now \nbeen taken into account. Our revised first epoch results are as \nfollows:\n\nUT               t-t0 (days)   Mag (Original)     Mag (Revised)\n2003-04-21.02    2.60          R=23.64 +/- 0.07   R=23.3 +/- 0.1\n2003-04-21.03    2.61          I=22.60 +/- 0.05   I=23.0 +/- 0.1\n\n\nThis message may be cited.",
  "circularId": 2236,
  "createdOn": 1053400359000,
  "email": "grr@space.mit.edu",
  "subject": "GRB 030418: Second Epoch Optical Observations with Magellan",
  "submitter": "George Ricker at MIT  <grr@space.mit.edu>",
  "eventId": "GRB 030418"
}