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GCN Circular 35373

GRB 231215A: Redshift from OSIRIS+ / GTC
2023-12-16T12:43:06Z (4 months ago)
Christina Thöne at ASU-CAS <>
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C. C. Thoene (ASU-CAS), A. de Ugarte Postigo (CNRS/OCA and LAM), J. F. Agui Fernandez (CAHA), L. Izzo (INAF/Capodimonte), J. P. U. Fynbo (DAWN/NBI), N. R. Tanvir (U. Leicester), M. Blazek (CAHA), S. Geier, A. Cabrera-Lavers, Fabricio Perez Toledo and Miguel Rivero (all GTC) report:
We obtained spectroscopy of the afterglow of GRB 231215A (D’Avanzo et al. GCN 35343, Evans et al. GCN 35345, Pankov et al. GCN 35349) with OSIRIS+ at the 10.4m GTC at a mean epoch of 0.4958 days after the GRB. The observation consisted of 3x900s exposures with grism R1000B, covering the range between 3700 and 7780 AA at a resolving power of about 600.

The spectrum shows a strong but reddened continuum with multiple absorption features. The highest redshift features include Lyman alpha, SII 1250,53,59, SiII1260, 1304, OI1302, CII 1334, SiIV1393, 1402, CIV 1548, 1550, AlII1670, FeII 1608, 1611 at a common redshift of z=2.305. We also identify fine structure lines of SiII* 1264 and 1309 at the same redshift, which we hence assume as the redshift of the GRB. Additionally, we detect two intervening systems, at z=2.076 showing CIV and SiIV absorption and at z=0.574 showing the MgII 2796, 2803 doublet.

We thank the GTC staff for excellent support. This GRB reached Earth on the name's day of the first author. 
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