ASASSN-15pz: Revealing Significant Photometric Diversity among 2009dc-like, Peculiar SNe Ia^∗

Abstract

We report comprehensive multi-wavelength observations of a peculiar Type Ia-like supernova ("SN Ia-pec") ASASSN-15pz. ASASSN-15pz is a spectroscopic "twin" of SN 2009dc, a so-called "Super-Chandrasekhar-mass" SN, throughout its evolution, but it has a peak luminosity M B,peak = −19.69 ± 0.12 mag that is ≈ 0.6 mag dimmer and comparable to the SN 1991T sub-class of SNe Ia at the luminous end of the normal width-luminosity relation. The synthesized 56 Ni mass of M56 Ni = 1.13 ± 0.14M is also substantially less than that found for several 2009dc-like SNe. Previous well-studied 2009dclike SNe have generally suffered from large and uncertain amounts of host-galaxy extinction, which is negligible for ASASSN-15pz. Based on the color of ASASSN-15pz, we estimate a host extinction for SN 2009dc of E(B − V ) host = 0.12 mag and confirm its high luminosity (M B,peak [2009dc] ≈ −20.3 mag). The 2009dc-like SN population, which represents ∼ 1% of SNe Ia, exhibits a range of peak luminosities, and do not fit onto the tight width-luminosity relation. Their optical light curves also show significant diversity of late-time ( 50 days) decline rates. The nebular-phase spectra provide powerful diagnostics to identify the 2009dc-like events as a distinct class of SNe Ia. We suggest referring to these sources using the phenomenology-based "2009dc-like SN Ia-pec" instead of "Super-Chandrasekhar SN Ia," which is based on an uncertain theoretical interpretation. a Nordic Optical Telescope (2.56 m) located at Roque de los Muchachos Observatory, La Palma in the Canary Islands; b du Pont telescope (2.5 m) located in Chile at Las Campanas Observatory; c New Technology Telescope (3.58 m) located in Chile at the La Silla Observatory; d One of the Magellan Telescopes (6.5 m) located at Las Campanas Observatory in Chile; e One of the Magellan Telescopes (6.5 m) located at Las Campanas Observatory in Chile

Variable Hα Emission in the Nebular Spectra of the Low-luminosity Type Ia SN2018cqj/ATLAS18qtd

“…In this paper, we present observations of the Type Ia SN2018cqj/ATLAS18qtd that show similarities to SN2018fhw/ASASSN-18tb, including the detection of an Hα emission line in late-time spectra of a lowluminosity SN Ia. The spectroscopic observations of SN2018cqj/ATLAS18qtd presented in this paper were obtained as part of the 100IAS survey Kollmeier et al 2019;Chen et al 2019), a project using 5-10 meter class telescopes to obtain nebular-phase optical spectra of a complete sample of ∼ 100 SNe Ia within z 0.02, in order to systematically study signatures of explosion asymmetries such as those discovered in SN2007on (Dong et al 2015). In Section §2.1 we discuss the discovery, spectroscopic classification, and host galaxy environment of SN2018cqj/ATLAS18qtd.…”

A Linear Relation Between the Color Stretch $s_{BV}$ and the Rising Color Slope $s_0^*(B-V)$ of Type Ia Supernovae

“…In this work, we analyze the B-and V -band light curves presented in Chen et al (2020). We include SNe Ia ranging from the most luminous end (i.e, 1991T-like) to the least luminous end (i.e., 1991bg-like) in the analysis, while we exclude several peculiar Ia-like objects that are known to deviate from the WLR (e.g., Iax-type objects such as SN 2017gbb classified by Lyman et al 2017 and the 2009dc-like SN Ia-peculiar, ASASSN-15pz studied by Chen et al 2019). In order to obtain accurate s BV measurements, we need to reliably infer the time of the B-band peak , t peak (B), and the time of maximum B − V color, t max (B − V ).…”

Nebular spectra of 111 Type Ia supernovae disfavour single-degenerate progenitors

“…Our sample also includes 4 "Super Chandrasekhar" (SC) SNe Ia explosions (SNe 2006gz, 2007if, 2009dc, and SNF 20080723-012), where the inferred ejecta mass, M e j , is higher than the Chandrasekhar mass of ≈ 1.4 M (e.g., Howell et al 2006;Scalzo et al 2019) although the nomenclature is currently debated (Chen et al 2019). The preferred formation theory of SC SNe Ia involves a DD merger of two WDs with a combined mass above the Chandrasekhar mass (Tutukov & Yungelson 1994;Howell 2001), although SD progenitors have also been proposed (Yoon & Langer 2005).…”