{
  "bibcode": "2018GCN.22724....1R",
  "body": "A. Rossi (INAF-OAS), J. Palmerio (IAP, Paris), J. Japelj (API, U. \nAmsterdam), D. Malesani (DAWN/NBI and DARK/NBI), N. R. Tanvir (Univ. \nLeicester), D. A. Kann (HETH/IAA-CSIC), J. P. U. Fynbo (DAWN/NBI), G. \nPugliese (API, U. Amsterdam),  A. de Ugarte Postigo (HETH/IAA-CSIC and \nDARK/NBI), K. E. Heintz (Univ. Iceland and DAWN/NBI), and S. D. Vergani \n(GEPI/Obs. Paris) report on behalf of the Stargate Consortium:\n\nWe observed the Swift/XRT afterglow localization of GRB 180512A (Swift \ntrigger 832119; Deich et al., GCN #22710) with the ESO VLT UT4 equipped \nwith the HAWK-I near-infrared imager. Observations started on 2018 May \n13 at 04:27 UT and ended at 05:28 UT, for a total of 36 min on source \nand corresponding to a midtime of ~7 hours after the GRB trigger. We do \nnot detect the optical source observed by Rossi et al. (GCN #22718), nor \nany other object within the XRT error circle, down to H > 22.8 (Vega), \ncalibrated against 2MASS field stars.\n\nMoreover, we note that after comparing the early GROND upper limit (r' > \n24.9; Bolmer, GCN #22714) with the Swift/XRT observations, we obtain an \noptical to X-ray spectral slope beta_OX < ~0.1 (using the convention \nF_nu ~ nu^-beta). This value is lower than the minimum expected \nfollowing standard afterglow modelling (beta_OX >= 0.5) and, together \nwith the r-band detection with LBT as well as the high X-ray column \ndensity (Burrows et al., GCN #22721), suggests that a combination of \nmoderate redshift, intrinsic faintness and dust extinction is \nresponsible for the faint optical afterglow.\n\nWe acknowledge the excellent support from the ESO staff, particularly \nCyrielle Opitom, Fuyan Bian, and Steffen Mieske in obtaining these \nobservations.",
  "circularId": 22724,
  "createdOn": 1526311696000,
  "email": "andrea.rossi@inaf.it",
  "subject": "GRB 180512A: VLT/HAWK-I NIR Observations",
  "submitter": "Andrea Rossi at INAF  <andrea.rossi@inaf.it>",
  "eventId": "GRB 180512A"
}