{
  "bibcode": "2018GCN.23256....1K",
  "body": "D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, \nDARK/NBI), L. Izzo, C. C. Thoene, M. Blazek, K. Bensch (all \nHETH/IAA-CSIC), and A. Sota (IAA/CSIC) report:\n\nWe observed the location of the extremely bright AGILE/Fermi GRB 180914B \n(Ursi et al., GCN #23226; Bissaldi et al., GCN #23232) with the T150 \ntelescope of the Sierra Nevada Observatory (OSN). We obtained 3 x 180 s \nimages in the Ic band, centered 3.157 days after the GRB.\n\nThe afterglow (e.g., Zheng & Filippenko, GCN #23237; Troja et al., GCN \n#23238; de Ugarte Postigo et al., GCN #23239) is clearly detected, and \nwe derive Ic (AB) = 20.28 +/- 0.06 mag vs. several SDSS comparison \nstars, using the transformation equations of Lupton (2005).\n\nUsing the photometry given in the GCNs so far (Zheng & Filippenko, GCN \n#23237; Troja et al., GCN #23238, #23243; de Ugarte Postigo et al., GCN \n#23239; Kuin, GCN #23241; Mazaeva et al., GCN #23244, #23249; Lipunov et \nal., GCN #23245; D'Avanzo et al., GCN #23246; Ramsay et al., GCN #23252; \nWatson et al., GCN #23253, Izzo et al., GCN #23255), we find the optical \nafterglow can be fit by an achromatic simple power-law with a decay \nslope alpha = 1.65 +/- 0.02 (taking host-galaxy magnitudes from SDSS \ninto account). The SED (from u to H band) is well-fit with a small \namount of SMC extinction, we find beta = 0.94 +/- 0.11, A_V = 0.09 +/- \n0.07 (assuming F_nu ~ t^(-alpha)*nu^(-beta) ). Note the earliest \ndetection, from MASTER, lies significantly below the back-extrapolation \nof the later decay slope, indicating a rebrightening may have taken \nplace.",
  "circularId": 23256,
  "createdOn": 1537382017000,
  "email": "kann@iaa.es",
  "subject": "GRB 180914B: OSN Detection and light curve/SED analysis",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 180914B"
}