Supernova Rates and Luminosity Functions from ASAS-SN III: Over a Decade of Type Ia SNe and Their Subtypes

TL;DR

This work delivers a high-precision measurement of the local SN Ia rate by combining 11 years of ASAS-SN data in the V and g bands, with robust completeness corrections that account for light-curve diversity. By applying subtype-specific light-curve templates and injecting simulated events, the authors derive the total rate $R_{ ext{tot}} = (2.55 \pm 0.12) \times 10^{4}$ yr$^{-1}$ Gpc$^{-3}$ h$^{3}_{70}$ at $z=0.029$, and provide detailed rates for subtypes including Ia-norm+other, Ia-91T, Iax, Ia-CSM, 02es-like, and 03fg-like. The luminosity functions reveal a broad SN Ia population, with a peak near $M_{g,\mathrm{peak}} \approx -19$ mag and a wide Iax LF extending to $M_{g,\mathrm{peak}} \approx -15$ mag, while 02es-like and 03fg-like SNe suggest a luminosity continuum tied to a shared progenitor channel. The extremely rare Ia-CSM population (about $0.036\%$ of the total) and the substantial disparity between 02es-like and 03fg-like rates place strong constraints on progenitor scenarios and the role of dust extinction, highlighting the need for deeper nearby surveys to fully characterize the faint end of the SN Ia LF. Overall, the paper establishes a benchmark local SN Ia rate with detailed subtype demographics and luminostiy distributions, informing models of SN Ia progenitors and chemical enrichment in the local universe.

Abstract

We present volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the All-Sky Automated Survey for Supernovae (ASAS-SN), covering the 11-year period from 2014 to 2024. By combining the 2014--2017 $V$-band sample with the 2018--2024 $g$-band sample, we construct a large statistical dataset of $1776$ SNe Ia. We compute completeness corrections based on injection-recovery simulations of the ASAS-SN light curves, taking into account the variations in light curve shapes. For our standard sample ($M_{g,\mathrm{peak}}<-16.0$ mag), we extract a total volumetric SN Ia rate of $R_{\mathrm{tot}} = (2.55 \pm 0.12) \times 10^4\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h_{70}^3$ at a median redshift of $z=0.029$. With a statistical uncertainty of $4.7\%$, this is the most precise local measurement to date. While the "normal" SNe Ia account for $(92.7 \pm 1.9)\%$ of this rate, the total LF reveals immense diversity, with $M_{g,\mathrm{peak}}$ spanning over five magnitudes. The LF of SNe Iax is also broad and rises toward lower luminosities, resulting in a likely lower limit of $(4.3 \pm 1.8)\%$ of the total rate. We place strong constraints on the rate of SNe Ia-CSM, finding they account for only $(0.036 \pm 0.017)\%$ of the total local rate. Finally, we find that the low-luminosity 02es-like SNe are $7 \pm 5$ times more common than the luminous 03fg-like SNe. This places demographic constraints on models proposing a physical continuum for these two subtypes, implying that any common channel for the two classes must strongly favor lower-luminosity explosions.

Figures (13)

• Figure 1: Fractions and numbers of all SNe discovered or recovered by ASAS-SN in $g$-band from UTC 2018-01-01 to UTC 2024-12-31.
• Figure 2: Peak apparent (top) and absolute (bottom) magnitude versus redshift distributions of the 2037 SNe Ia discovered or recovered by ASAS-SN (gray). The filled circles and filled histograms show our $g$-band standard sample of 1366 SNe Ia. Open gray points are the SNe excluded by our standard cuts on peak absolute magnitude $M_{g,\mathrm{peak}}$, Galactic latitude $b$, peak apparent magnitude $m_{g,\mathrm{peak}}$, and redshift $z$, as marked by the gray dotted lines.
• Figure 3: The ASAS-SN $g$-band detection performance. Top: The probability of flagging a source as a detection in a single epoch as a function of SNR for each year. The colored points show binned efficiency estimates from the data, and the solid lines are the best fits from Equation \ref{['eq:efficiency']}. Bottom: The completeness fraction as a function of peak apparent magnitude per year for a typical normal SN Ia ($M_{g,\text{peak}} = -19.0$ mag). While the single-epoch efficiency (top) saturates much below unity, the high cadence of ASAS-SN ensures a higher total detection probability for brighter transients (bottom).
• Figure 4: Top: Completeness fraction ($F_1$) for all years combined for the templates used for normal SNe Ia. Bottom: Completeness fraction ($F_1$) for all years combined for other subtypes of SNe Ia. The dashed red line marks the standard limiting magnitude of $g=17.5\,\mathrm{mag}$.
• Figure 5: Left: Rate as a function of the Galactic latitude cut. Middle: Rate as a function of the limiting apparent magnitude. Right: Rate as a function of faintest peak absolute magnitude cut. In all three panels, the numbers are the number of SNe in each bin. The red points in each panel are the values used for our standard sample.