Photometry and Spectroscopy of SN 2024pxl: A Luminosity Link Among Type Iax Supernovae

TL;DR

SN 2024pxl is an extensively observed nearby Type Iax supernova whose photometric and spectroscopic data place it between the high- and low-luminosity Iax groups. Analytical modeling of the integrated SED light curve yields a synthesized $M(^{56}{\rm Ni})\approx 0.027\,M_\odot$ and an ejecta mass of $M_{\rm ej}\approx 0.36\,M_\odot$, consistent with a weak deflagration of a CO white dwarf, specifically the N1def scenario. The spectral evolution—including early C6580 and weak Si lines, next-to-maximum Si and Fe features, and late-time Fe/Co-dominated emission—along with velocity measurements, supports substantial mixing of ejecta and a transitional nature between brighter and fainter Type Iax SNe. UV, optical, and NIR data collectively position SN 2024pxl as a luminosity link that helps unify the diverse Iax population and constrains progenitor/explosion mechanisms in these peculiar thermonuclear events. The work also aligns with recent JWST findings, reinforcing a continuum rather than discrete sub-classes within Type Iax SNe and highlighting the value of multiwavelength, high-cadence campaigns for understanding explosion physics in white-dwarf systems.

Abstract

We present extensive ultraviolet to optical photometric and optical to near-infrared (NIR) spectroscopic follow-up observations of the nearby intermediate-luminosity ($M_V = -16.81\pm0.19$~mag) Type Iax supernova (SN) 2024pxl in NGC 6384. SN~2024pxl exhibits a faster light curve than the high-luminosity members of this class, and slower than low-luminosity events. The observationally well-constrained rise time of $\sim$11 days and an estimated synthesized $^{56}$Ni mass of 0.03\, M$_\odot$, based on analytical modeling of the integrated spectral energy distribution light curve, are consistent with models of the weak deflagration of a carbon-oxygen white dwarf. Our optical spectral sequence of SN~2024pxl shows weak \ion{Si}{2} lines and spectral evolution similar to other high-luminosity Type Iax SNe, but also a prominent early-time \ion{C}{2} line, like lower-luminosity Type Iax SNe. The late-time optical spectrum of SN~2024pxl closely matches that of SN~2014dt, and its NIR spectral evolution aligns with that of other well-studied, high-luminosity Type Iax SNe. The spectral-line expansion velocities of SN~2024pxl are at the lower end of the Type Iax SN velocity distribution, and the velocity distribution of iron-group elements compared to intermediate-mass elements suggests that the ejecta are mixed on large scales, as expected in pure deflagration models. SN~2024pxl exhibits characteristics intermediate between those of high-luminosity and low-luminosity Type~Iax SNe, further establishing a link across this diverse class.

Figures (22)

• Figure 1: A power-law fit to the early-time photometry of SN 2024pxl in ATLAS cyan, orange, and ZTF g and r filters. Nondetections are indicated in the shaded region.
• Figure 2: Light-curve evolution of SN 2024pxl in uBgVrRiIz and clear bands. Corresponding absolute magnitudes corrected for extinction are also presented on the right-hand ordinate axis.
• Figure 3: Light-curve evolution of SN 2024pxl in the Swift bands.
• Figure 4: Comparison of the light-curve evolution of SN 2024pxl in BgVri bands with other well-studied Type Iax SNe. The B-band maximum date serves as the reference for comparison plots in both B and V bands, while gri-band comparison plots are referenced to g-band maximum brightness.
• Figure 5: Comparison of the light-curve evolution of SN 2024pxl in the Swift UVW1 band with other Type Iax SNe.