{
  "bibcode": "2015GCN.18510....1D",
  "body": "S. Dichiara (U. Ferrara, ICRANet), D. Kopac (U. Ljubljana), C. Guidorzi \n(U. Ferrara), S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of \na larger collaboration report:\n\nThe 1-m LCOGT McDonald observatory began observing Swift GRB 151027A \n(Maselli et al. GCN 18478) on October 28, 01:29:27 UT (0.90 days after \nthe burst trigger) with SDSS R and I filters. We clearly detect the \noptical afterglow (Maselli et al.; Zheng & Filippenko GCN 18479; Elenin \net al. GCN 18480; Perley & Cenko GCN 18481; Xu et al. GCN 18485) with \nthe following magnitudes:\n\nMid Time      Exposure       Filter       Magnitude\n(days)           (s)\n-------------------------------------------------------\n0.90            5x120         R           16.87 +- 0.04\n0.91            6x120         I           17.26 +- 0.05\n-------------------------------------------------------\n\nCalibration is done against nearby USNOB-1 star RA(J2000)=18:09:53.742, \nDEC(J2000)=+61:20:57.27, assuming R2=17.21 mag and I=17.17 mag. We note \nthe presence of another USNOB-1 object at RA(J2000)=18:09:56.489, \nDEC(J2000)=+61:21:10.64, lying at 3.1 arcsec from the GRB afterglow.",
  "circularId": 18510,
  "createdOn": 1446034569000,
  "email": "guidorzi@fe.infn.it",
  "subject": "GRB 151027A: LCOGT-McDonald afterglow observations",
  "submitter": "Cristiano Guidorzi at Ferrara U,Italy  <guidorzi@fe.infn.it>",
  "eventId": "GRB 151027A"
}