GRB 221009A: VLT spectroscopic detection of the host galaxy
Abstract
We observed the optical counterpart of GRB 221009A (Dichiara et al., GCN 32632; Veres et al., GCN 32636; and very many other GRB satellites) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. A 40-min spectrum was secured covering the wavelength range 3000-25000 AA, with a mean time 2022 October 14.02 UT (4.46 days after the Fermi/GBM trigger). From the acquisition image, we measure for the optical counterpart a magnitude i = 19.89 +- 0.05 (AB; calibrated against Pan-STARRS), 4.45 days after the Fermi/GBM trigger. The continuum is still dominated by the afterglow. However, narrow emission lines can be seen from the host galaxy. We identify H alpha in the optical and Pa alpha in the near-infrared, at redshift z = 0.151, consistent with the one measured from the afterglow absorption features (de Ugarte Postigo et al., GCN 32648). The H alpha FWHM is about 110 km s^-1. From the H alpha flux, corrected for Galactic extinction (A_V = 4.2 mag), we infer a SFR > 0.25 M_Sun yr^-1 (this value is a lower limit due to unaccounted host extinction and slit losses). We acknowledge expert support from the ESO observing staff in Paranal, in particular Zahed Wahhaj and Matias Jones.
- Publication:
-
GRB Coordinates Network
- Pub Date:
- October 2022
- Bibcode:
- 2022GCN.32765....1I