Unveiling SN 2022eyw: A Bright Member of the Type Iax Supernova Subclass

TL;DR

SN 2022eyw is a luminous Type Iax supernova with $M_g \approx -{17.8}$ mag and a rise time of about $15$ days, placing it among the brighter Iax events. Through comprehensive photometry, spectroscopy, and radiative-transfer modelling with \\textit{TARDIS}, the ejecta are found to be well mixed and Fe-group dominated, with traces of unburnt carbon consistent with incomplete burning in a pure deflagration scenario. A semi-analytic Arnett analysis yields ${M}_{Ni} \approx 0.12\,M_\odot$, ${M}_{ej} \approx 0.79\,M_\odot$, and ${E}_{k} \approx 0.19\times 10^{51}$ erg, while the spectral evolution echoes the behavior of bright Iax like SNe 2002cx and 2012Z. Model comparisons place SN 2022eyw between the N3-def and N5-def pure deflagration templates, supporting a low-energy, partial disruption with potentially a bound remnant, though discrepancies in red-band evolution and Ni–ejecta coupling indicate current models are not fully describing the brightest cases. Overall, the findings reinforce pure deflagration of a near-Chandrasekhar-mass CO WD as a viable mechanism for luminous SNe Iax and motivate more detailed multidimensional modelling and broader observational coverage.

Abstract

We present comprehensive photometric and spectroscopic observations of Supernova (SN) 2022eyw, a luminous member of the Type Iax SN subclass. SN 2022eyw reached a peak absolute magnitude of $M_g = -17.80\pm0.15$ mag and exhibited a rise time of $\sim$15 days, placing it among the brighter Iax events. The bolometric light curve indicates a synthesized $^{56}$Ni mass of $0.120\pm0.003~\text{M}_{\odot}$, with an estimated ejecta mass of $0.79\pm0.09~\text{M}_{\odot}$ and kinetic energy of $0.19\times10^{51}$ erg. The spectral evolution from -8 to +110 days past maximum reveals features characteristic of bright Type Iax Supernovae, including a transition from Fe III to Fe II dominance, moderate expansion velocities, and a lack of strong C III absorption. TARDIS spectral modelling of the early-phase spectra indicates a well-mixed ejecta dominated by Fe-group elements. In addition, traces of unburnt carbon are detected, pointing to incomplete burning as expected in pure deflagration models. Late-time spectral evolution shows a blend of permitted and forbidden lines. Comparison with deflagration models suggests that SN 2022eyw originated from a partial deflagration of a Chandrasekhar-mass white dwarf, with explosion properties intermediate between the N3-def and N5-def models. These observations support pure deflagration of a CO white dwarf as a viable explosion mechanism for its luminous members.

Figures (14)

• Figure 1: $B$-band image of the SN 2022eyw field, with a field of view of approximately $9.5' \times 9.5'$. The image was taken using 2-m HCT on 2022 March 26 with an exposure time of 360 seconds. The SN is marked with a blue crosshair, and the secondary standard stars used for photometric calibration are enclosed with blue circles.
• Figure 2: Light curve evolution of SN 2022eyw in $UBg'Vr'i'z'$ bands. $B$-band maximum is used to calculate the phase which is plotted on the x-axis. The y-axis shows the apparent magnitudes in the respective bands, shifted by a constant for a clear representation. The light curve in each band is plotted with its corresponding error bars. However, the uncertainties are relatively small, causing the error bars to be mostly concealed behind the data markers. All the magnitudes are in the Vega system. We have used the Vega-AB magnitude conversion factors (2007AJ....133..734B) to convert the $g'r'i'z'$ magnitudes to the Vega system from the AB system.
• Figure 3: $(B-V)$, $(V-R)$, $(g-r)$ and $(r-i)$ color evolution of SN 2022eyw, plotted alongside a comparison sample of other well-observed SNe Iax. All colors are corrected for extinction. Dark colored small markers are used to represent bright SNe Iax while soft colored large markers are used to represent faint SNe Iax.
• Figure 4: Pseudo-bolometric light curve of SN 2022eyw (red circles) constructed using the $BgVri$ filter set, compared with other bright SNe Iax: SN 2002cx, SN 2005hk, SN 2012Z, SN 2018cni, SN 2020rea, SN 2020udy, and faint ones: SN 2008ha, SN 2010ae, SN 2020kyg. The inset highlights the difference in luminosity when $U$ and $z^{\prime}$ bands are included in the integration, resulting in a higher peak pseudo-bolometric flux.
• Figure 5: One-dimensional (along the diagonal) and two-dimensional projections of the posterior distribution of the parameters of the fit. The 16th, 50th, and 84th percentiles are shown as dashed lines.