{
  "bibcode": "2012GCN.13257....1S",
  "body": "S. Schulze (Univ. Iceland), A. J. Levan (Univ. Warwick), D. Malesani \n(DARK/NBI), J. P. U. Fynbo (DARK/NBI), N. R. Tanvir (Univ. Leicester), \nB. Milvang-Jensen (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and \nDARK/NBI), V. D'Elia (ASI/ASDC and INAF/OAR), J. Sollerman (OKC, \nStockholm), J. Hjorth (DARK/NBI), report on behalf of the X-shooter GRB \nGTO collaboration:\n\nWe observed the optical counterpart of GRB 120422A (Troja et al., GCN \n13243; Cucchiara et al., GCN 13245) with the ESO VLT equipped with the \nX-shooter spectrograph. Observations started on 2012 April 22.99 UT \n(16.5 hr after the GRB), for a total exposure time of 80 min in each of \nthe UVB, VIS, and NIR arms, covering the wavelength range 3000-25000 AA. \nThe slit was aligned so to cover both the galaxy at z = 0.28 present in \nthe SDSS (Cucchiara et al., GCN 13245; Tanvir et al., GCN 13251) and the \nGRB optical counterpart (Cucchiara et al., GCN 13245).\n\nWe detect a plethora of nebular emission lines from the candidate host \ngalaxy, including [O II], [O III], Balmer lines up to Hzeta, [N II], [S \nII], at a common redshift z = 0.283, thus confirming the results of \nTanvir et al. (GCN 13251).\n\nThe trace of the GRB counterpart is rather blue (see also Nardini et \nal., GCN 13256), and we detect Mg II at z = 0.283 in absorption. No \nfurther absorption features are visible. We also note that the spatial \nextent of the brightest emission lines from the SDSS galaxy encompasses \nthe position of the GRB counterpart, indicating nebular emission at z = \n0.283 at the GRB position.\n\nWhile a chance superposition cannot be excluded, we note that the lack \nof absorption features at z > 0.283 would require a very tenuous \nenvironment at the GRB location. Furthermore, the UVOT detection in all \nthe UV filters (Kuin & Troja, GCN 13248) implies a low redshift z <~ \n1.3. Last, we note that the UVOT photometry at t ~ 5 ks after the burst \nreveals a very blue spectrum, which is not typical of GRB afterglows, \nbut is reminiscent of the very blue early emission of GRB 060218 \n(Campana et al. 2006, Nature, 442, 1008). We thus conclude that the GRB \nis also likely at z = 0.283.\n\nUsing the gamma-ray fluence reported by Barthelmy et al. (GCN 13246), at \nz = 0.283 the isotropic-equivalent energy release of GRB 120422A is \n~4.4*10^49 erg, which is typical of local GRBs, often associated with \nsupernovae. We encourage photometric and spectroscopic follow-up to \ndetect the emergence of a supernova, or lack thereof.\n\nWe acknowledge the excellent support of the ESO observing staff in \nParanal, in particular Henri Boffin and Giovanni Carraro. We thank Nino \nCucchiara for providing us with a finding chart from the Gemini \nobservation (GCN 13245).",
  "circularId": 13257,
  "createdOn": 1335172403000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "GRB 120422A: VLT/X-shooter spectroscopy of the GRB counterpart",
  "submitter": "Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>",
  "eventId": "GRB 120422A"
}