{
  "subject": "GRB 221009A: VLT spectroscopic detection of the host galaxy",
  "eventId": "GRB 221009A",
  "bibcode": "2022GCN.32765....1I",
  "createdOn": 1665852966000,
  "circularId": 32765,
  "submitter": "Daniele B Malesani at Radboud U  <d.malesani@astro.ru.nl>",
  "email": "d.malesani@astro.ru.nl",
  "body": "L. Izzo (DARK/NBI), A. Saccardi (GEPI, Observatoire de Paris), J. P. U. \nFynbo (DAWN/NBI), J. Palmerio (GEPI, Paris obs.), D. B. Malesani \n(Radboud Univ. and DAWN/NBI), J. F. Agui Fernandez (IAA/CSIC), D. A. \nKann (Goethe Univ.), A. Melandri (INAF/OAR), S. D. Vergani (GEPI, Paris \nobs.), K. Wiersema (Lancaster univ.), report on behalf of the Stargate \nconsortium:\n\nWe observed the optical counterpart of GRB 221009A (Dichiara et al., GCN \n32632; Veres et al., GCN 32636; and very many other GRB satellites) \nusing the ESO VLT UT3 (Melipal) equipped with the X-shooter \nspectrograph. A 40-min spectrum was secured covering the wavelength \nrange 3000-25000 AA, with a mean time 2022 October 14.02 UT (4.46 days \nafter the Fermi/GBM trigger).\n\n From the acquisition image, we measure for the optical counterpart a \nmagnitude i = 19.89 +- 0.05 (AB; calibrated against Pan-STARRS), 4.45 \ndays after the Fermi/GBM trigger.\n\nThe continuum is still dominated by the afterglow. However, narrow \nemission lines can be seen from the host galaxy. We identify H alpha in \nthe optical and Pa alpha in the near-infrared, at redshift z = 0.151, \nconsistent with the one measured from the afterglow absorption features \n(de Ugarte Postigo et al., GCN 32648).\n\nThe H alpha FWHM is about 110 km s^-1. From the H alpha flux, corrected \nfor Galactic extinction (A_V = 4.2 mag), we infer a SFR > 0.25 M_Sun \nyr^-1 (this value is a lower limit due to unaccounted host extinction \nand slit losses).\n\nWe acknowledge expert support from the ESO observing staff in Paranal, \nin particular Zahed Wahhaj and Matias Jones."
}