{
  "bibcode": "2017GCN.20606....1C",
  "body": "B. E. Cobb (GWU) reports:\n\nUsing the ANDICAM instrument on the 1.3m telescope at CTIO, we\nobtained optical/IR imaging of the error region of GRB 170202A\n(GCN 20575, Racusin et al.) at three different epochs: 0.41671\n[2017-02-03 04:28 UT], 0.53096 [2017-02-03 07:13 UT] and 2.39175\n[2017-02-05 03:52 UT] days post-burst. At each epoch, total summed\nexposure times amounted to 36 minutes in I and 30 minutes in J.\n\nThe afterglow of GRB 170202A (e.g. GCN 20575, Racusin et al.;\nGCN 20576, Xin et al.; GCN 20578, Lipunov et al.) is detected\nin our early images, with the preliminary magnitudes (and 3-sigma\nlimits) listed below. Note that the optical photometry is calibrated\nagainst USNO-B1.0 stars in the field, so suffers from a large\nphotometric calibration error of about +/-0.3 magnitudes, which has\nnot been included in the errors quoted below. The IR photometry\nis calibrated against the single 2MASS star in our field-of-view,\nso similarly may include a large (but unknown) calibration error.\n\nmid-exposure time\n(days post-burst)  I mag             J mag\n0.41671                20.1+/-0.1      18.9+/-0.1\n0.53096                20.6+/-0.1      >18.5\n2.39175                >21.0             >18.6",
  "circularId": 20606,
  "createdOn": 1486313709000,
  "email": "bcobb@gwu.edu",
  "subject": "GRB 170202A: SMARTS optical/IR afterglow observations",
  "submitter": "Bethany Cobb at GWU  <bcobb@gwu.edu>",
  "eventId": "GRB 170202A"
}