{
  "bibcode": "1998GCN...134....1H",
  "body": "J. P. Halpern (Columbia), and R. Fesen (Dartmouth) report on behalf\nof the MDM Observatory GRB follow-up team that the optical afterglow of\nGRB 980613 discovered by Hjorth et al. (GCN #109) is also present and\nvariable on MDM images at a level just below the limit of I = 22.3\npreviously quoted by us in GCN #106.\n\nOur J2000 position of the OT is (+/- 0.6\"):\n\nRA  =  10 17 57.82\nDec = +71 27 25.5\n\nMeasured magnitudes (at mean epoch) and 1-sigma statistical errors are:\n\nR = 22.96 +/- 0.09  (June 14.24 UT)\nI = 22.53 +/- 0.09  (June 14.20 UT)\nI = 22.83 +/- 0.15  (June 15.19 UT)\n\nActual errors are larger, limited by systematic effects of fringing in the\nI band.  Photometry was calibrated using Landolt standards.  Our magnitudes\nof the five reference stars measured by Diercks et al. (GCN #108) are given\nin the following table, and are in agreement with their values, as well as those\nof Djorgovski et al. (GCN #117).  Quoted uncertainties are 1-sigma statistical.\nCoordinates are measured with respect to the USNO A1.0 reference system.\n\nStar    RA(2000)     Dec(2000)            R                 I \n-------------------------------------------------------------------- \n 1    10 17 47.52   +71 26 59.9     17.91 +/- 0.01    17.34 +/- 0.01\n 2    10 17 54.87   +71 27 39.8     19.20 +/- 0.01    18.76 +/- 0.01\n 3    10 18 06.61   +71 27 04.7     20.02 +/- 0.05    18.72 +/- 0.01 \n 4    10 17 55.31   +71 28 16.3     19.54 +/- 0.02    18.61 +/- 0.01\n 5    10 17 41.44   +71 28 08.9     18.70 +/- 0.01    18.31 +/- 0.01\n--------------------------------------------------------------------\n\nOur measurement of R = 22.96 for the OT on June 14.24 is similar to that\nof Hjorth et al. (R = 22.9 +/- 0.2 on June 13.89), which may be consistent\nwith a plateau in the first 24 hours after the burst, or perhaps just an\neffect of the large error bars.  Our R-band measurement combined with the\nlater detection by Djorgovski et al. (R = 24.5 +/- 0.5 on June 16.30)\nimplies a power-law decay slope of 1.3.\n\nOur images are posted at http://cba.phys.columbia.edu/grb/980613/\n\nThis message may be cited.",
  "circularId": 134,
  "createdOn": 899835182000,
  "email": "jules@astro.columbia.edu",
  "subject": "GRB980613 Optical Observations",
  "submitter": "Jules Halpern at Columbia U.  <jules@astro.columbia.edu>",
  "eventId": "GRB 980613"
}