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ZTF SN Ia DR2 follow-up: Early excess in Type Ia supernova light curves
Journal article   Open access   Peer reviewed

ZTF SN Ia DR2 follow-up: Early excess in Type Ia supernova light curves

Tomás E. Müller-Bravo, Kate Maguire, Alaa Alburai, Umut Burgaz, Georgios Dimitriadis, Lluís Galbany, Joel Johansson, Young-Lo Kim, Chang Liu, Adam A. Miller, …
Astronomy and astrophysics (Berlin), Forthcoming
10 Aug 2026
DOI: https://doi.org/10.1051/0004-6361/202659826
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url
https://doi.org/10.1051/0004-6361/202659826View
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Abstract

There is a general consensus that Type Ia supernovae ( comprise the thermonuclear explosions of a C/O white dwarf (WD) in a binary system. However, the nature of their progenitors and explosion mechanism still remains elusive. Their early light curves can offer strong constraints on these parameters, as they trace the outermost layers and provide evidence of their initial conditions. In this work, we study the Zwicky Transient Facility (ZTF) data release 2 sample of in search for objects with early flux excess ( 17 $,mag). We found that the best Two main approaches were used: i) finding deviations between early-time observations and models without early excess and ii) finding an agreement between observations and models with early excess. For the former approach, different methods, such as power-law and SALT2 fits, were used to identify candidates. For the second approach, we used double-detonation (DD) and companion-interaction (CI) models, finding 145 and 199 candidates, respectively. In general, there is a disagreement between the methods in the exact objects identified as as well as in their number. By combining multiple methods, we found 17 strong candidates, 6 of which are of the overluminous subtype (five 91T-like and one 03fg-like). The most prominent excesses reach ∼10-17% of peak flux (up to $∼- candidates have higher stretch on average compared to the rest of the They also seem to prefer lower mass and bluer host galaxies, potentially linked to younger stellar populations. Additionally, we estimated the fraction of to be łesssim25% of all in agreement with previous works, with overluminous subtypes having a higher relative fraction compared to normal When studying the parameter distribution of the DD models for the candidates, we see a preference for intermediate WD core mass (1, a lower fraction of shell burning (20%), and heavier He-burning products (∋ckel). For the CI models, we see no trends with any of the parameters. We are unable to draw strong conclusions on whether one model is preferred over the other as a viable description of explosions Finally, we highlight the challenge of identifying in łq real time, making the triggering of early-time spectroscopic observations for these objects a difficult task.

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