Hierarchical Bayesian power-law fits to early ZTF light curves of 972 SNe Ia yield population parameters for rise time, index, and color evolution, revealing a bifurcation with SALT2 stretch.
Not All Who Wander Are Lost: Early Excess Demographics in the Volume-limited ZTF DR2 SN Ia Sample
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abstract
Early-time flux excesses in Type Ia supernovae (SNe~Ia) offer a unique insight into their progenitor systems and explosion mechanisms. Although individual early-excess events and larger searches have been reported, demographic studies remain limited by sample size. We present a systematic search for early-time excess emission in a volume-limited sample ($z<0.06$) of SNe~Ia based on the Zwicky Transient Facility Data Release 2 (ZTF DR2). Using ZTF $g$- and $r$-band light curves, we identify candidates showing early-excesses shortly after the explosion time, and we apply conservative coverage and quality requirements to build reliable ``excess'' and ``no-excess'' bump and no-bump catalogs. From an initial sample of 1547 SNe~Ia, our final catalogs contain 42 early-excess and 110 no-excess events. We compare the two populations using SN and host environment parameters from ZTF DR2 and quantify the differences using two-sample statistical tests. We find the strongest differences are in SN light-curve properties: early-excess events have larger SALT2 stretch $x_1$ ($7.91\sigma$) and larger $r$-band secondary-maximum flux $\mathcal{F}_{r_2}$ ($6.25\sigma$), while differences in SALT2 color $c$ are weak ($0.57\sigma$). Early-excess events also favor bluer $(g-z)_{\rm local}$ ($3.41\sigma$) and lower $\log_{10} (M_*/M_\odot)_{\rm local}$ ($2.73\sigma$). Our results connect early excesses with SNe~Ia diversity, and motivate further analyses of upcoming larger samples.
years
2026 2verdicts
UNVERDICTED 2representative citing papers
A two-population Bayesian model of Type Ia supernovae and hosts fitted to ZTF DR2 data yields a luminosity gap, different stretch slopes, and host-dependent extinctions while rendering separate host-galaxy step corrections redundant.
citing papers explorer
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Decoding the Early-Time Light Curves of Type Ia Supernovae. II. Population Parameters of One Thousand ZTF Supernovae
Hierarchical Bayesian power-law fits to early ZTF light curves of 972 SNe Ia yield population parameters for rise time, index, and color evolution, revealing a bifurcation with SALT2 stretch.
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Two-population model of type Ia supernovae and their associations with host galaxies in ZTF DR2
A two-population Bayesian model of Type Ia supernovae and hosts fitted to ZTF DR2 data yields a luminosity gap, different stretch slopes, and host-dependent extinctions while rendering separate host-galaxy step corrections redundant.