{
  "bibcode": "2017GCN.21799....1D",
  "body": "A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo (HETH/IAA-CSIC)\nC.C. Thoene (HETH/IAA-CSIC), D.A. Kann (HETH/IAA-CSIC), \nK.E. Heintz (DARK/NBI), N. Castro-Rodriguez (GRANTECAN, IAC, ULL), \nA. Marante (GRANTECAN) report on behalf of a larger collaboration:\n\nWe have observed the field of GRB 170903A (Markwardt et al., GCN 21793) \nwith OSIRIS at the 10.4m GTC telescope. Observations started at 20:49 UT \n(8.0 hrs after the burst). Observations consisted of an acquisition image in \ni-band and 3x900s spectra with the R1000B grism, which covers the range \nbetween 3700 and 7880 AA.\n\nThe acquisition image shows a single source within the refined XRT error box\n(Goad et al., GCN 21797), with an i-band magnitude (AB) of 23.17 +/- 0.15. \nThe object appears unresolved at a seeing of 0.6���. Spectroscopy of it shows a \nweak trace covering the complete range above 4000 AA and a single, very \nprominent emission feature. Due to the strength of this feature and the \nnon-detection of any other features in the spectral range, we identify it as the \nunresolved [OII] 3727/3729 doublet at a redshift of 0.886, which we propose \nas the redshift of the host galaxy and hence of the GRB.",
  "circularId": 21799,
  "createdOn": 1504480576000,
  "email": "deugarte@iaa.es",
  "subject": "GRB 170903A: Host galaxy redshift from OSIRIS/GTC",
  "submitter": "Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>",
  "eventId": "GRB 170903A"
}