{
  "bibcode": "2020GCN.29100....1M",
  "body": "D. B. Malesani (DTU Space), J.-B. Vielfaure (APC, Paris University), L. \nIzzo (DARK/NBI), S. D. Vergani (GEPI, Observatoire de Paris), D. \nBurgarella (AMU, CNRS, CNES, LAM), V. D'Elia (ASI/SSDC), A. de Ugarte \nPostigo (HETH/IAA-CSIC, DARK/NBI), J. P. U. Fynbo (DAWN/NBI), A. J. \nLevan (Radboud Univ.), B. Milvang-Jensen (DAWN/NBI), D. A. Kann \n(HETH/IAA-CSIC), E. Palazzi (INAF/OAS), G. Pugliese (API, Univ. \nAmsterdam), N. R. Tanvir (Univ. Leicester), K. Wiersema (Univ. Warwick), \nreport on behalf of the Stargate consortium:\n\nWe observed the field of GRB 201221A (Page et al., GCN 29096) using the \nESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.\n\nUsing the acquisition camera, multi-band imaging was secured. Within the \nXRT error circle (Evans, GCN 29097), no source is detected in an r-band \nimage (taken at mean epoch of 42 min after the GRB) down to limiting \nmagnitude r > 23.5 (AB). However, a source is clearly visible in the \nz-band image with z = 19.76 +- 0.04 AB (mean time 35 min after the GRB). \nThe corresponding color r-z > 3.7 is exceptionally red. The coordinates \nof the object are (J2000, 0.3\" error):\n\nRA = 14:17:55.26\nDec = -45:24:58.0\n\nSpectroscopy of the z-band source was executed covering the wavelength \nrange 3000-25000 AA. Unfortunately due to visibility constraints, only \ntwo spectra by 600 s each were secured, plus two extra exposures during \ntwilight which have lower quality. We report on the analysis of the \nfirst set only, which has a mean time of 1.65 hr after the GRB.\n\nContinuum is well detected in the infrared arm, as well as in the red \npart of the visible arm. A clear break is detected around 8150 AA, \nwhich, if interpreted as the Lyman break, corresponds to z = 5.70. Weak \ncontinuum is detected blueward of the break, until it vanishes \ncompletely at the corresponding location of the Lyman limit. We thus \nconclude that z = 5.70 is the redshift of GRB 201221A.\n\nFurther analysis is undergoing.\n\nWe acknowledge support from the ESO observing staff at Paranal, in \nparticular Zahed Wahhaj.",
  "circularId": 29100,
  "createdOn": 1608556560000,
  "email": "malesani@space.dtu.dk",
  "subject": "GRB 201221A: VLT/X-shooter afterglow discovery and spectroscopic redshift z = 5.7",
  "submitter": "Daniele B Malesani at DTU Space  <malesani@space.dtu.dk>",
  "eventId": "GRB 201221A"
}