Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu

Abstract

We present photometric and spectroscopic observations and analysis of SN 2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova (SN). SN 2021bxu is unique, showing a large initial decline in brightness followed by a short plateau phase. With $M_r=-15.93\pm 0.16\mathrm{mag}$ during the plateau, it is at the lower end of the luminosity distribution of stripped-envelope supernovae (SE-SNe) and shows a distinct $\sim$10 day plateau not caused by H- or He-recombination. SN 2021bxu shows line velocities which are at least $\sim 1500\mathrm{km}{\mathrm{s}}^{-1}$ slower than typical SE-SNe. It is photometrically and spectroscopically similar to Type IIb SNe during the photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find that the bolometric light curve is best described by a composite model of shock interaction between the ejecta and an envelope of extended material, combined with a typical SN IIb powered by the radioactive decay of ${}^{56}$Ni. The best-fit parameters for SN 2021bxu include a ${}^{56}$Ni mass of $M_{\mathrm{Ni}}=0.029_{-0.005}^{+0.004}{\mathrm{M}}_{\odot }$, an ejecta mass of $M_{\mathrm{ej}}=0.61_{-0.05}^{+0.06}{\mathrm{M}}_{\odot }$, and an ejecta kinetic energy of $K_{\mathrm{ej}}=8.8_{-1.0}^{+1.1}\times 10^{49}\mathrm{erg}$. From the fits to the properties of the extended material of Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing envelope mass. SN 2021bxu has $M_{\mathrm{Ni}}$ on the low end compared to SE-SNe and Ca-rich SNe in the literature, demonstrating that SN 2021bxu-like events are rare explosions in extreme areas of parameter space. The progenitor of SN 2021bxu is likely a low mass He star with an extended envelope.

18 pages, 15 figures, accepted to MNRAS

References in corpus (25)

• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• Characterizing the V-band light-curves of hydrogen-rich type II supernovae
• PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
• Design and operation of the ATLAS Transient Science Server
• The Supernova Channel of Super-AGB Stars
• SOUSA: the Swift Optical/Ultraviolet Supernova Archive
• The Carnegie Supernova Project I: Third Photometry Data Release of Low-Redshift Type Ia Supernovae and Other White Dwarf Explosions
• Revisiting the Lick Observatory Supernova Search Volume-Limited Sample: Updated Classifications and Revised Stripped-Envelope Supernova Fractions
• A Sample of Type II-L Supernovae
• Investigating the properties of stripped-envelope supernovae, what are the implications for their progenitors?
• Analysis of Late--time Light Curves of Type IIb, Ib and Ic Supernovae
• The AMUSING++ Nearby Galaxy Compilation: I. Full Sample Characterization and Galactic--Scale Outflows Selection
• SN 2013df, a double-peaked IIb supernova from a compact progenitor and an extended H envelope
• Shock Cooling Emission from Extended Material Revisited
• SN2019dge: a Helium-rich Ultra-Stripped Envelope Supernova
• High-Cadence, Early-Time Observations of Core-Collapse Supernovae From the TESS Prime Mission
• Type II supernovae from the Carnegie Supernova Project-I. I. Bolometric light curves of 74 SNe II using uBgVriYJH photometry
• A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone can Explain Early-Excess Blue Flux in Some Type Ia Supernovae
• Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey
• SN 2018gjx reveals that some SNe Ibn are SNe IIb exploding in dense circumstellar material
• Calcium-rich Transient SN 2019ehk in A Star-Forming Environment: Yet Another Candidate for An Ultra-Stripped Envelope Supernova
• Swift-XRT Follow-up of Gravitational Wave Triggers in the Second Advanced LIGO/Virgo Observing Run

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