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GCN Circular 35730

GRB 240209A: Classification of AT2024cew/GOTO24pw as Type Ia-pec supernova
2024-02-14T22:00:51Z (2 months ago)
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K. Ackley; D. Steeghs; B. P. Gompertz; M. Magee; J. Lyman; R. Starling; M. J. Dyer; K. Ulaczyk; F. Jimenez-Ibarra; A. Kumar; D. O'Neill; D. K. Galloway; V. Dhillon; P. O'Brien; G. Ramsay; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration and the GOTO-FAST program:

We report on the classification of AT2024cew/GOTO24pw as part of the GOTO-FAST program (Godson et al., The source was first reported by GOTO (Belkin et al, GCN 35715) as a possible optical counterpart to GRB 240209A (Fermi GBM team, GCN 35712). It showed an initial decline across the GOTO epochs which was consistent with the ZTF photometry obtained through the Lasair broker (Smith et al. 2019).

Following the reported brightening of the source (de Ugarte Postigo et al., GCN 35716) we obtained spectroscopic observations on the night of 2024-02-13 with the Isaac Newton Telescope (INT) using the IDS spectrograph with R150V grating (3950-7900 A, R~600). The INT spectrum is consistent with a Type Ia-pec SN at a redshift of z=0.15 (Godson et al. 2024, AT2024cew is therefore unrelated to GRB 240209A. 

At this distance, the ongoing brightening measured by NOT (de Ugarte Postigo et al., GCN 35716), Wendelstein (Busmann et al., GCN 35724), and OHP (Turpin et al., GCN 35725) implies an absolute magnitude of -19.5. This is luminous for normal type Ia SNe and is consistent with peculiar SN Ia classification.

Based on observations made with the Isaac Newton Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

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