An analysis of the Type Ia SN 2024gy and a comparison of different host extinction estimation techniques

Terwel, Jacco H., Maguire, Kate, O'Donnell, Cillian, Pursiainen, Miika, Casasbuenas, Alba and Inserra, Cosimo ORCID: https://orcid.org/0000-0002-3968-4409 2026. An analysis of the Type Ia SN 2024gy and a comparison of different host extinction estimation techniques. Astronomy & Astrophysics 712 , A173. 10.1051/0004-6361/202659568

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Abstract

Type Ia supernovae (SNe Ia) are well-known standardisable candles, and are one of the main ways to measure the distance to their host galaxies. However, extinction due to interstellar dust causes objects to appear fainter and redder. Correcting for this requires estimating the amount of intervening material and how the extinction changes as a function of wavelength. We present and analyse optical and near-infrared data of the well-observed SN 2024gy and use these to compare different extinction estimation techniques, making use of photometric, spectroscopic, and polarimetric data. SN 2024gy is a normal SN Ia with high velocity (HV) components in Si IIλ6355 (phase < −10 days) and a particularly strong HV feature in the Ca II near-infrared triplet (up to peak). Modelling SN 2024gy with TARDIS shows better matches with a double-detonation scenario compared to a delayed-detonation scenario due to a better match to the Ca II HV component. A measurement of the stable Ni/Fe ratio, however, favours a delayed-detonation scenario. Host extinction estimates range from E(B − V)host = 0.12 ± 0.02 mag (narrow interstellar absorption lines) to E(B − V)host = 0.24 ± 0.06 mag (Lira law) with a mean of E(B − V)host = 0.22 ± 0.04 mag, assuming RV = 3.1. The spread between different methods highlights the challenge of accurately estimating the amount of extinction light suffers before being observed.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physical, Chemical & Environmental Sciences Schools > Physics and Astronomy
Additional Information:	Full list of authors available: https://doi.org/10.1051/0004-6361/202659568
Publisher:	EDP Sciences
ISSN:	0004-6361
Date of First Compliant Deposit:	4 September 2026
Date of Acceptance:	27 May 2026
Last Modified:	04 Sep 2026 09:30
URI:	https://orca.cardiff.ac.uk/id/eprint/189391

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