GCN Circular 34385

A. Martin-Carrillo (UCD), A. J. Levan (Radboud), A. de Ugarte Postigo (OCA/CNRS), L. Izzo (INAF-OACN and DARK/NBI), B. Schneider (MIT), T. Laskar (Utah), B. P. Gompertz (U. Birmingham), D. B. Malesani (Radboud and DAWN/NBI), G. Finneran (UCD), J.F. Agui Fernandez (IAA-CSIC),  C.C. Thoene (ASU-CAS), V. D'Elia (ASI-SSDC and INAF-OAR), N.R. Tanvir (U. Leicester), P. Jakobsson (U. Iceland) and G. Pugliese (API, Amsterdam) report on behalf of a larger collaboration:

We obtained spectroscopic observations of the orphan GRB afterglow candidate ZTF23aaoohpy/AT2023lcr
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 (Andreoni et al., GCN 3402
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; Swain et al., GCN 34022
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; Kumar et al., GCN 34025
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; Adami et al., GCN 34030
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; Perley et al., GCN 34031
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; Jiang et al., GCN 34040
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; Chen et al., GCN 34043
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) with the James Webb Space Telescope on 12 August 2023 (DDT program 4554, PI Martin-Carrillo). This was about 55 days (27 days rest frame) after the likely explosion epoch of the event (Gompertz et al., GCN 34023
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). Observations were obtained with the NIRSpec clear prism in the 0.5-5.3 micron wavelength range.

Assuming a redshift of z=1.027 (Perley et al. GCN 34041
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), the obtained spectrum shows an excellent match to the spectrum of GRB-SN 1998bw (at 22 days) and 2017iuk (at 26 days), confirming the presence of a supernova component initially hinted by photometric observations (Martin-Carrillo et al., GCN 34370
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). Based on the observed spectral properties, we identify the supernova associated to ZTF23aaoohpy/AT2023lcr
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 as a broad-lined type Ic SN similar to other SNe accompanying GRBs. To date, this is the furthest GRB-SN association with robust spectroscopic confirmation.

Further analysis and observations are ongoing.

We thank the staff of STScI for their work to get these observations rapidly scheduled, in particular Alison Vick, Tony Keyes, Mario Gennaro and Armin Rest.