Constraining Type Ia supernova explosions and early flux excesses with the Zwicky Transient Factory

Abstract

In the new era of time-domain surveys Type Ia supernovae are being caught sooner after explosion, which has exposed significant variation in their early light curves. Two driving factors for early time evolution are the distribution of 56 Ni in the ejecta and the presence of flux excesses of various causes. We perform an analysis of the largest young SN Ia sample to date. We compare 115 SN Ia light curves from the Zwicky Transient Facility to the model grid containing light curves of Chandrasekhar-mass explosions with a range of 56 Ni masses, 56 Ni distributions and explosion energies. We find that the majority of our observed light curves are well reproduced by Chandrasekhar-mass explosion models with a preference for highly extended 56 Ni distributions. We identify six SNe Ia with an early-time flux excess in our gr-band data (four 'blue' and two 'red' flux excesses). We find an intrinsic rate of 18±11 per cent of early flux excesses in SNe Ia at z < 0.07, based on three detected flux excesses out of 30 (10 per cent) observed SNe Ia with a simulated efficiency of 57 per cent. This is comparable to rates of flux excesses in the literature but also accounts for detection efficiencies. Two of these events are mostly consistent with CSM interaction, while the other four have longer lifetimes in agreement with companion interaction and 56 Ni-clump models. We find a higher frequency of flux excesses in 91T/99aa-like events (44±13 per cent).

Early Lightcurves of Type Ia Supernovae are Consistent with Nondegenerate Progenitor Companions

“…Our value is consistent with other estimates for the rate of early excesses in SNe Ia, such as Deckers et al (2022) (early excess rate of 18 ± 11%) and (rate of ∼22%, 5 out of 23 SNe), even though these studies do not adopt the same null hypothesis as we do (single-degenerate systems with companion interaction). Jiang et al (2018) find a rate of 100% in 91T-like/99aa-like SNe Ia, based on six out of six overluminous SNe Ia with early excesses.…”

“…On the other hand, it makes it a possible diagnostic of whether or not there is an early excess: when Miller et al (2020a) fit general power laws to the rising lightcurves of a sample of 127 SNe Ia observed with ZTF, they found no instances of early excesses. But Deckers et al (2022), reexamining 115 SNe Ia from that sample with the model grid here, were able to recover six instances of early excesses based on quantitative measures of whether all models produced poor fits to the earliest epochs. This also shows that the statement "this SN does/does not have an early excess" can be dependent on the methodology used to characterize these excesses.…”

“…Other objects have unusual early data, such as SN 2018aoz, which showed extreme color evolution in the hours after explosion (Ni et al 2022). Some papers in the literature have noted objects with weaker early excesses without providing detailed models for any one event (Jiang et al 2018;Deckers et al 2022) , and other work has established some limits on the rates of early excesses based on non-detections in samples of SNe Ia (Bianco et al 2011;Brown et al 2012;Olling et al 2015;Fausnaugh et al 2021).…”