{
  "bibcode": "1998GCN...108....1D",
  "body": "A. Diercks, E.W. Deutsch, C. Stubbs (U. of Washington);\nP.M. Vreeswijk, T.J. Galama (U. of Amsterdam); J. van Paradijs (U. of\nAmsterdam; U. of Alabama in Huntsville); C. Robinson, and\nC. Kouveliotou (USRA at MSFC-NASA) report:\n\nWe observed the BeppoSAX error box of GRB 980613 on June 14.35 UT and\nJune 15.35 UT in Kron-Cousins I with the APO 3.5m telescope.\nConditions were mostly clear with ~2.0 arcsec seeing.\n\nPhotometry on a 30 min series of I-band (Kron-Cousins) images centered\naround June 14.35 UT (28 hr after the burst) yields the following\npreliminary magnitudes and relative uncertainties for several\nreference stars:\n\nID  I mag  Rel Err     RA   (J2000)   DEC\n--  -----  ------   ------------------------\n1   17.28    0.02   10 17 47.48  +71 27  0.6\n2   18.74    0.02   10 17 54.83  +71 27 40.2\n3   18.70    0.03   10 18  6.55  +71 27  5.1\n4   18.58    0.02   10 17 55.29  +71 28 16.5\n5   18.25    0.02   10 17 41.45  +71 28  9.3\n\nAbsolute calibration is based on a single observation of the PG\n2213-006 standard field (Landolt 1992) and a previously determined\nairmass correction for this filter and instrument.  The uncertainty in\nthe absolute calibration is 0.1 mag.\n\nThe limiting magnitude (SNR~5) for the combined images for each of the\nJune 14.35 and 15.35 epochs is I~22.0.  We find no object at the\nposition of the slow moving K~17.5 detection reported by\nCastro-Tirado(GCN #102,#103).\n\nThe error circle was also observed with the 1m JKT telescope in Harris\nI on June 13.97 for 1600s and June 14.96 for 420s.  Conditions were\nclear with ~2.0 arcsec seeing.\n\nDifference imaging between the June 13.97 UT JKT data and the June\n14.35 UT APO data reveals no point sources which varied by more than\nthe flux equivalent of I = 20.6 mags between the two images.  Similar\nanalysis on June 14.35 UT and June 15.35 UT APO data gives an upper\nlimit of 21.5 mags to any such flux differences.\n\nAn image of the field is posted at:\nhttp://www.astro.washington.edu/deutsch/grb/grb980613/\n\nThis note can be cited.",
  "circularId": 108,
  "createdOn": 898180640000,
  "email": "diercks@astro.washington.edu",
  "subject": "GRB 980613 optical observations",
  "submitter": "Alan Diercks at U.Washington  <diercks@astro.washington.edu>",
  "eventId": "GRB 980613"
}