SN 2024bfu, SN 2025qe, and the early light curves of type Iax supernovae

TL;DR

This paper presents early observations of two Type Iax supernovae, SN 2024bfu and SN 2025qe, revealing their rise times, early light curve shapes, and spectral features, providing insights into their explosion mechanisms and differences from normal Type Ia supernovae.

Contribution

The study provides some of the earliest observations of SNe Iax shortly after explosion, analyzing their early light curves and spectra to compare with normal SNe Ia and test explosion models.

Findings

SN 2025qe observed within 2 days of first light

SNe Iax have shorter rise times than normal SNe Ia

SNe Iax show lower rise indices, indicating different ejecta mixing

Abstract

Type Iax supernovae (SNe Iax) are one of the most common subclasses of thermonuclear supernova and yet their sample size, particularly those observed shortly after explosion, remains relatively small. In this paper we present photometric and spectroscopic observations of two SNe Iax discovered shortly after explosion, SN 2024bfu and SN 2025qe. Both SNe were observed by multiple all-sky surveys, enabling tight constraints on the moment of first light and the shape of the early light curve. Our observations of SN 2025qe begin <2d after the estimated time of first light and represent some of the earliest observations of any SN Iax. Spectra show features consistent with carbon absorption throughout the evolution of SN 2025qe, potentially indicating the presence of unburned material throughout the ejecta. We gather a sample of SNe Iax observed by ATLAS, GOTO, and ZTF shortly after explosion and measure their rise times and early light curve power-law rise indices. We compare our results to a sample of normal SNe Ia and find indications that SNe Iax show systematically shorter rise times, consistent with previous work. We also find some indication that SNe Iax show systematically lower rise indices than normal SNe Ia. The low rise indices observed among SNe Iax are qualitatively consistent with extended $^{56}$Ni distributions and more thoroughly-mixed ejecta compared to normal SNe Ia, similar to predictions from pure deflagration explosions.