Faintest of them all : ZTF 21aaoryiz/SN 2021fcg -- Discovery of an extremely low luminosity type Iax supernova

Abstract

We present the discovery of ZTF 21aaoryiz/SN 2021fcg -- an extremely low-luminosity Type Iax supernova. SN 2021fcg was discovered by the Zwicky Transient Facility in the star-forming galaxy IC0512 at a distance of $\approx$ 27 Mpc. It reached a peak absolute magnitude of $M_r=$ $-12.66\pm 0.20$ mag, making it the least luminous thermonuclear supernova discovered to date. The E(B-V) contribution from the underlying host galaxy is unconstrained. However, even if it were as large as 0.5 mag, the peak absolute magnitude would be $M_r=-13.78\pm 0.20$ mag -- still consistent with being the lowest luminosity SN. Optical spectra of SN 2021fcg taken at 37 and 65 days post maximum show strong [Ca II], Ca II and Na I D emission and several weak [Fe II] emission lines. The [Ca II] emission in the two spectra has extremely low velocities of $\approx 1300$ and $1000$ km s${}^{-1}$ respectively. The spectra very closely resemble those of the very low luminosity Type Iax supernovae SN 2008ha, SN 2010ae and SN 2019gsc taken at similar phases. The peak bolometric luminosity of SN 2021fcg is $\approx$ $2.5_{-0.3}^{+1.5}\times 10^{40}$ erg s${}^{-1}$ which is a factor of three lower than that for SN 2008ha. The bolometric lightcurve of SN 2021fcg is consistent with a very low ejected nickel mass (M${}_{\mathrm{Ni}}\approx 0.8_{-0.5}^{+0.4}\times 10^{-3}$ M${}_{\odot }$). The low luminosity and nickel mass of SN 2021fcg pose a challenge to the picture that low luminosity SNe Iax originate from deflagrations of near M${}_{\mathrm{ch}}$ hybrid carbon-oxygen-neon white dwarfs. Instead, the merger of a carbon-oxygen and oxygen-neon white dwarf is a promising model to explain SN 2021fcg.

arXiv commentaccepted for publication in ApJL. 10 pages, 5 figures

References in corpus (46)

• emcee: The MCMC Hammer
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• ATLAS: A High-Cadence All-Sky Survey System
• The Zwicky Transient Facility: Science Objectives
• The HST Key Project on the Extragalactic Distance Scale. XXVIII. Combining the Constraints on the Hubble Constant
• Type Iax Supernovae: A New Class of Stellar Explosion
• SN 2002cx: The Most Peculiar Known Type Ia Supernova
• Design and operation of the ATLAS Transient Science Server
• The Zwicky Transient Facility: Observing System
• Three-dimensional pure deflagration models with nucleosynthesis and synthetic observables for Type Ia supernovae
• Kinematics of the Local Universe XIII. 21-cm line measurements of 452 galaxies with the Nançay radiotelescope, JHK Tully-Fisher relation and preliminary maps of the peculiar velocity field
• Proper image subtraction - optimal transient detection, photometry and hypothesis testing
• The Broad-lined Type Ic SN 2003jd
• The SED Machine: a robotic spectrograph for fast transient classification
• Fully-Automated Reduction of Longslit Spectroscopy with the Low Resolution Imaging Spectrometer at Keck Observatory
• Galaxy Groups within 3500 km s${}^{-1}$
• SN 2008ha: An Extremely Low Luminosity and Extremely Low Energy Supernova
• 3D deflagration simulations leaving bound remnants: a model for 2002cx-like Type Ia supernovae
• High luminosity, slow ejecta and persistent carbon lines: SN 2009dc challenges thermonuclear explosion scenarios
• A low energy core-collapse supernova without a hydrogen envelope
• Failed-Detonation Supernovae: Sub-Luminous Low-Velocity Ia Supernovae and Their Kicked Remnant White Dwarfs with Iron-Rich Cores
• Real-bogus classification for the Zwicky Transient Facility using deep learning
• A luminous, blue progenitor system for a type-Iax supernova
• Optical Light Curves of the Type Ia Supernovae 1990N and 1991T
• The GROWTH Marshal: A Dynamic Science Portal for Time-Domain Astronomy
• Rapidly Decaying Supernova 2010X: A Candidate ".Ia" Explosion
• A Fully Automated Integral Field Spectrograph Pipeline for the SEDMachine: pysedm
• The Zwicky Transient Facility Alert Distribution System
• Deflagrations in hybrid CONe white dwarfs: a route to explain the faint Type Iax supernova 2008ha
• An Unusually Fast-Evolving Supernova
• Comprehensive Observations of the Bright and Energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar Mass White Dwarf Explosion
• The Zwicky Transient Facility Census of the Local Universe I: Systematic search for Calcium rich gap transients reveal three related spectroscopic sub-classes
• EC-SNe from super-AGB progenitors: theoretical models vs. observations
• ZTF Early Observations of Type Ia Supernovae I: Properties of the 2018 Sample
• Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
• Optical and Near-IR Observations of the Faint and Fast 2008ha-like Supernova 2010ae
• The type Iax supernova, SN 2015H: a white dwarf deflagration candidate
• Hybrid C-O-Ne white dwarfs as progenitors of type Ia supernovae: dependence on Urca process and mixing assumptions
• Wait for it: Post-supernova winds driven by delayed radioactive decays
• Double-Degenerate Carbon-Oxygen and Oxygen-Neon White Dwarf Mergers: A New Mechanism for Faint and Rapid Type Ia Supernovae
• X-rays observations of a super-Chandrasekhar object reveal an ONeMg and a CO white dwarf merger product embedded in a putative SN Iax remnant
• The lowest of the low: discovery of SN 2019gsc and the nature of faint Iax supernovae
• Observations of the low-luminosity Type Iax supernova 2019gsc: a fainter clone of SN 2008ha?