Nebular H$\alpha$ Limits for Fast Declining Type Ia Supernovae

Abstract

One clear observational prediction of the single degenerate progenitor scenario as the origin of type Ia supernovae (SNe) is the presence of relatively narrow ($\approx$1000 km s${}^{-1}$) H$\alpha$ emission at nebular phases, although this feature is rarely seen. We present a compilation of nebular phase H$\alpha$ limits for SN Ia in the literature and demonstrate that this heterogenous sample has been biased towards SN Ia with relatively high luminosities and slow decline rates, as parameterized by $\Delta$m${}_{15}(B)$, the difference in $B$-band magnitude between maximum light and fifteen days afterward. Motivated by the need to explore the full parameter space of SN~Ia and their subtypes, we present two new and six previously published nebular spectra of SN Ia with $\Delta$m${}_{15}(B)$$>$1.3 mag (including members of the transitional and SN1991bg-like subclasses) and measure nondetection limits of $L_{H\alpha }$$<$0.85--9.9$\times$10${}^{36}$ ergs s${}^{-1}$, which we confirmed by implanting simulated H$\alpha$ emission into our data. Based on the lastest models of swept-up material stripped from a nondegenerate companion star, these $L_{H\alpha }$ values correspond to hydrogen mass limits of $M_H$$\lesssim$1-3$\times$10${}^{-4}$ $M_{\odot }$, roughly three orders of magnitude below that expected for the systems modeled, although we note that no simulations of H$\alpha$ nebular emission in such weak explosions have yet been performed. Despite the recent detection of strong H$\alpha$ in ASASSN-18tb (SN 2018fhw; $\Delta$m${}_{15}(B)$ = 2.0 mag), we see no evidence that fast declining systems are more likely to have late time H$\alpha$ emission, although a larger sample is needed to confirm this result.

11 pages, 3 figures, two tables. ApJ Letters accepted

References in corpus (13)

• Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies
• CfA3: 185 Type Ia Supernova Light Curves from the CfA
• Constraining the Type Ia Supernova Progenitor: The Search for Hydrogen in Nebular Spectra
• The Carnegie Supernova Project I: Third Photometry Data Release of Low-Redshift Type Ia Supernovae and Other White Dwarf Explosions
• ESC and KAIT Observations of the Transitional Type Ia SN 2004eo
• Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor
• No trace of a single-degenerate companion in late spectra of SNe 2011fe and 2014J
• Early Observations and Analysis of the Type Ia SN 2014J in M82
• Nebular-Phase Spectra of Nearby Type Ia Supernovae
• Subclasses of Type Ia Supernovae as the origin of [α/Fe] ratios in dwarf spheroidal galaxies
• Nebular Spectroscopy of Kepler's Brightest Supernova
• The ANU WiFeS SuperNovA Program (AWSNAP)
• Reddened, Redshifted, or Intrinsically Red? Understanding Near-Ultraviolet Colors of Type Ia Supernovae