{
  "bibcode": "2013GCN.14273....1X",
  "body": "D. Xu, D. Malesani, T. Kruehler, J. P. U. Fynbo (DARK/NBI), D. A.\nPerley (Caltech), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), L. Kaper\n(U. Amsterdam), A. de Ugarte Postigo (IAA-CSIC and DARK/NBI), N. R.\nTanvir (U. Leicester) report on behalf of the X-shooter GTO GRB\ncollaboration:\n\nWe observed the field of GRB 111123A (Stamatikos et al., GCN 12587)\nusing the Keck-I telescope equipped with the LRIS instrument.\nObservations were carried out on 2013 February 10 (~444 days after the\nburst), simultaneously in the g and I bands, for a total exposure time\nof 750 and 720 s, respectively.\n\nAn extended source with g=25.83 (AB) and I = 23.55 (Vega) is detected\nat the position of the optical and NIR afterglow (Xu et al., GCN\n12589; Fugazza et al., GCN 12593), where the positional error radius\nof the optical afterglow has been reduced from ~1.0\" to ~0.3\" through\na refined analysis. We thus consider the source to be the host galaxy\nof GRB 111123A.\n\nA spectrum of this source was taken on 2013 March 07 with the ESO VLT\nequipped with the X-shooter spectrograph, featuring NIR/VIS/UVB three\narms and covering the wavelength range 3000-25000 AA. The exposure\ntime was 4x600 s. In the NIR arm, we detect four emission lines,\ninterpreted as [O III] (5007), [NeIII] (3869), [O II] (3727), and\nHbeta (a marginal detection), all at a common redshift z = 3.1516. In\nthe UVB arm, the host continuum is detected down to ~5100 AA, thus\ncorresponds to the onset of the Lyman alpha forest at the proposed\nredshift.\n\nWe acknowledge excellent support from the observing staff at Mauna Kea\nand Paranal, in particular Emanuela Pompei, Claudio Melo, and Andres\nPino.",
  "circularId": 14273,
  "createdOn": 1362740397000,
  "email": "dong.dark@gmail.com",
  "subject": "GRB 111123A: Keck-I host detection and VLT/X-shooter redshift",
  "submitter": "Dong Xu at DARK/NBI  <dong.dark@gmail.com>",
  "eventId": "GRB 111123A"
}