SN 2019ein: A Type Ia Supernova Likely Originated from a Sub-Chandrasekhar-Mass Explosion

Abstract

We present extensive optical photometric and spectroscopic observations for the nearby Type Ia supernova (SN Ia) 2019ein, spanning the phases from $\sim 3$ days to $\sim 330$ days after the explosion. This SN Ia is characterized by extremely fast expansion at early times, with initial velocities of Si II and Ca II being above ~ 25,000--30,000 km/s. After experiencing an unusually rapid velocity decay, the ejecta velocity dropped to ~ 13,000 km/s around maximum light. Photometrically, SN 2019ein has a moderate post-peak decline rate ($\Delta m_{15}(B)=1.35\pm 0.01$ mag), while being fainter than normal SNe Ia by about 40% (with $M_B^{\max }\approx -18.71\pm 0.15$ mag). The nickel mass synthesized in the explosion is estimated to be 0.27--0.31 $M_{\odot }$ from the bolometric light curve. Given such a low nickel mass and a relatively high photospheric velocity, we propose that SN 2019ein likely had a sub-Chandrasekhar-mass white dwarf (WD) progenitor, $M_{\mathrm{WD}}\lesssim 1.22M_{\odot }$. In this case, the explosion could have been triggered by a double-detonation mechanism, for which 1- and 2-dimensional models with WD mass $M_{\mathrm{WD}}\approx 1M_{\odot }$ and a helium shell of 0.01 $M_{\odot }$ can reasonably produce the observed bolometric light curve and spectra. The predicted asymmetry as a result of double detonation is also favored by the redshifted Fe II and Ni II lines observed in the nebular-phase spectrum. Possible diversity in origin of high velocity SNe Ia is also discussed.

34 pages, 16 figures, accepted for publication in MNRAS

References in corpus (32)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
• Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Improved Distances to Type Ia Supernovae with Multicolor Light Curve Shapes: MLCS2k2
• The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star
• CfA3: 185 Type Ia Supernova Light Curves from the CfA
• Improved Distances to Type Ia Supernovae with Two Spectroscopic Subclasses
• The Spectroscopic Diversity of Type Ia Supernovae
• SOUSA: the Swift Optical/Ultraviolet Supernova Archive
• The Carnegie Supernova Project: Intrinsic Colors of Type Ia Supernovae
• Optical and Near-Infrared Observations of the Highly Reddened, Rapidly Expanding Type Ia Supernova 2006X in M100
• Type Ia Supernovae as Stellar Endpoints and Cosmological Tools
• Evidence for Two Distinct Populations of Type Ia Supernovae
• SN 2003du: 480 days in the Life of a Normal Type Ia Supernova
• Optical Spectroscopy of Type Ia Supernovae
• ESC and KAIT Observations of the Transitional Type Ia SN 2004eo
• Exploring the spectral diversity of low-redshift Type Ia supernovae using the Palomar Transient Factory
• Nebular spectra and abundance tomography of the type Ia supernova SN 2011fe: a normal SN Ia with a stable Fe core
• Double Detonations with Thin, Modestly Enriched Helium Layers Can Make Normal Type Ia Supernovae
• Lick Observatory Supernova Search Follow-Up Program: Photometry Data Release of 93 Type Ia Supernovae
• Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
• Nebular-Phase Spectra of Nearby Type Ia Supernovae
• ZTF 18aaqeasu (SN 2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar Mass White Dwarf
• The early spectral evolution of SN 2004dt
• Type Ia Supernova Spectral Features in the Context of Their Host Galaxy Properties
• Infrared Surface Brightness Fluctuation Distances for MASSIVE and Type Ia Supernova Host Galaxies
• Berkeley Supernova Ia Program: Data Release of 637 Spectra from 247 Type Ia Supernovae
• High-Velocity Type Ia Supernova Has a Unique Host Environment
• Constraints on Circumstellar Material Around the Type Ia Supernova 2007af
• Observations of the Very Young Type Ia Supernova 2019np with Early-excess Emission
• Can Helium-detonation Model Explain the Observed Diversity of Type Ia Supernovae?

Cited by in corpus (2)

• Direct Analysis of the Broad-Line SN 2019ein: Connection with the Core-Normal SN 2011fe
• Prospects of the multi-channel photometric survey telescope in the cosmological application of Type Ia supernovae