{
  "bibcode": "2022GCN.31453....1R",
  "body": "A. Rossi, F. Cusano, E. Palazzi, L. Amati (INAF-OAS Bologna), D. B. \nMalesani (Radboud U. Nijmegen and DAWN/NBI), S. Savaglio (UNICAL), on \nbehalf of the CIBO collaboration, and D. A. Kann (HETH/IAA-CSIC) report:\n\nWe report the results of spectroscopic observations of two galaxies \nclose to the position of the GRB (O'Connor et al. GCN #30934, Kann et \nal., GCN #30983) of the short GRB 210919A (Tohuvavohu et al., GCN \n#30846), obtained with the Multi-Object Double Spectrographs (MODS) \ninstrument mounted on the 2x8.4-m LBT telescope (Mt. Graham, AZ, USA). \nSpectra were obtained at a mid-time of 12:35 UT on 2021-10-16, ~27.5 \ndays after the burst trigger, for a total on-source time of 5400 s, \ncovering the wavelength range 3200-10000 AA.\n\nThe MODS slit inclination was adjusted to cover the positions of the two \nobjects singled out by O'Connor et al. (GCN #30934), with offsets of \n~3.4 and 13\" with respect to the candidate afterglow by Kann et al. \n(GCNs #30883 and #30884) respectively, and of the faint source at the \neastern edge of the XRT error circle detected in the ESO-VLT/FORS2 \nimages (Kann et al., GCN #30983). This latter source was not detected in \nthe MODS data. The spectra of the other two galaxies show several well \ndetected emission lines which we interpret as [OII] 3727AA, H-beta, \n[OIII] 4959,5007AA and H-alpha at a common redshift for both sources of \nz=0.2411. The clear detection of these emission lines, and especially \nH-beta, indicates that these are two star forming galaxies.\n\nAt this redshift, the projected distances to the two galaxies at ~3.4\" \nand ~13\" from the afterglow corresponds to ~13 and ~50 kpc. The distance \nbetween the two galaxies corresponds to 63 kpc, similar to the distance \nbetween the Milky Way and the SMC. There is at least another galaxy (RA, \nDEC = 05:21:04.01, +01:18:49.23) within 0.5 arcmin with similar \nphotometric redshifts (SDSS DR16), suggesting that the two galaxies are \nprobably not isolated, but part of a larger group.\n\nIf GRB 210919A was at z = 0.2411, using standard cosmology (Planck 2016) \nand the analysis of the BAT spectra (Barthelmy et al., GCN #30863 and \nhttp://gcn.gsfc.nasa.gov/notices_s/1073893/BA), we find that it would be \nconsistent with the population of short GRBs in the Ep,i - Eiso plane.\n\nWe acknowledge the excellent support from the LBTO and LBT-INAF staff, \nparticularly D. Thompson, S. Allanson, and S. Paiano, in obtaining these \nobservations.",
  "circularId": 31453,
  "createdOn": 1642269132000,
  "email": "andrea.rossi@inaf.it",
  "subject": "GRB 210919A: LBT spectroscopic redshift of the host galaxy candidates",
  "submitter": "Andrea Rossi at INAF  <andrea.rossi@inaf.it>",
  "eventId": "GRB 210919A"
}