{
  "bibcode": "2011GCN.12343....1M",
  "body": "D. Malesani (DARK, NBI), P. Jakobsson (U. Iceland), A. de Ugarte Postigo \n(DARK, NBI), J. Lykke (NOT), D. Xu (WIS), and N. R. Tanvir (U. \nLeicester) report on behalf of a larger collaboration:\n\nUsing ALFOSC on the Nordic Optical Telescope (NOT) we have obtained \nR-band (3 x 600 s) and z-band (18 x 300 s) imaging of the GRB 110915A \nfield (Holland et al., GCN 12335) starting on 2011 September 15.87 UT \n(around 7.5 hr after the burst).\n\nWe do not detect any object within the refined XRT error circle (Evans \net al., GCN 12340). The limiting magnitudes are R(Vega) = 24.3 and z(AB) \n= 23.5, calibrated against the USNO-B1 and SDSS catalogs, respectively.\n\nUsing our R-band limit and preliminary X-ray fluxes, we obtain a \ncorresponding upper limit on beta_OX of around 0.1, rendering the burst \ndark according to the definition proposed by Jakobsson et al. (2004, \nApJ, 617, L21). This burst may therefore be at high redshift, or suffer \nfrom significant dust extinction. The presence of significant excess \nabsorption in the X-ray afterglow spectrum \n(http://www.swift.ac.uk/xrt_spectra/00503219/) makes the second option \nmore likely.",
  "circularId": 12343,
  "createdOn": 1316132796000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "GRB 110915A: NOT observations",
  "submitter": "Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>",
  "eventId": "GRB 110915A"
}