A Study of Two Type IIb Supernovae: SNe 2008aq and 2019gaf

TL;DR

This study compares two Type IIb supernovae, analyzing their spectra, velocities, and progenitor masses, revealing differences in explosion energy and progenitor characteristics through photometric, spectroscopic, and modeling approaches.

Contribution

It provides detailed observational and modeling analysis of SNe 2008aq and 2019gaf, highlighting differences in velocities, energies, and progenitor masses among Type IIb supernovae.

Findings

SN 2019gaf has higher velocities and explosion energy than SN 2008aq.

Both SNe show transition from hydrogen to helium dominance within a month.

Progenitor masses are estimated between 13-25 M$_\\odot$, suggesting binary system origins.

Abstract

We present photometric and spectroscopic studies of two core-collapse supernovae (SNe) 2008aq and 2019gaf in the optical wavelengths. Light curve and spectral sequence of both the SNe are similar to those of other Type IIb SNe. The pre-maximum spectrum of SN~2008aq showed prominent H $\alpha$ lines, the He lines started appearing in the near maximum spectrum. The near maximum spectrum of SN~2019gaf shows shallow H$\alpha$ absorption and He lines with almost similar strength. Both the SNe show transition from hydrogen-dominated spectra to helium-dominated spectra within a month after maximum brightness. The velocity evolution of SN~2008aq matches well with those of other well-studied Type IIb SNe, while SN~2019gaf shows higher velocities. Close to maximum light, the H $\alpha$ and He I line velocities of SN~2019gaf are $\sim$ 2000 km sec$^{-1}$ and $\sim$ 4000 km sec$^{-1}$ higher than other well-studied Type IIb SNe. Semi-analytical modeling indicates SN~2019gaf to be a more energetic explosion with a smaller ejecta mass than SN~2008aq. The zero-age main-sequence (ZAMS) mass of the progenitor estimated using the nebular spectra of SN~2008aq ranges between 13 to 20 M$_\odot$, while for SN~2019gaf, the inferred ZAMS mass is between 13 to 25 M$_\odot$. The [O I] to [Ca II] lines flux ratio favors a less massive progenitor star in a binary system for both the SNe.