Type IIb SN 2024abfo light curves

We perform photometry on archival DECam imaging to derive the spectral energy distribution of the progenitor candidate and investigate its temporal variability. We consider single and binary star models to explain the end point of the progenitor candidate in the Hertzsprung-Russell diagram. For the supernova we compare the light curves and spectra with other SNe IIb with progenitor detections.

We derive the bolometric light curve and attempt to fit this with a semi-analytic light curve model. The position of the supernova in our adaptive optics imaging agrees with the progenitor position to within 20 mas. The progenitor SED is consistent with an A3V star with a radius of ~120 solar radii, a temperature of ~8800K, and a luminosity of log(L/L_{sun_})~4.9.

Single star models predict an initial mass in the range 12-16 M_sun, while the most probable binary model is a 12+1.2M_{sun}_ system with an initial period of 1.73 years. We also find significant evidence for variability of the progenitor candidate in the years prior to core-collapse. SN 2024abfo is the least luminous SN IIb with a direct progenitor detection.

At late times the r-band light curve decays more slowly than the comparison SNe, which may be due to increased gamma-ray trapping, although this requires further investigation. Similar to SN 2008ax, SN 2024abfo does not show a prominent double-peaked light curve. Our semi- analytic light curve modelling shows that this may be due to a very low mass of hydrogen <0.006 M_sun in the outer envelope.

Spectrally, SN 2024abfo is most similar to SN 2008ax at early times while at later times (~80 days) it appears to show persistent Halpha absorption compared to the comparison sample. We prefer a binary system to explain SN 2024abfo and its progenitor, although we are unable to rule out single-star models. We recommend late-time observations to search for a binary companion and signatures of CSM-interaction.

The absence of these features would support the hypothesis that SN 2024abfo resulted from a system which underwent a period of binary mass transfer well before (>1000~yr) the explosion, resulting in a low-mass (<0.01M_{sun}_) hydrogen-rich envelope.