SN 2019ehk: A Double-Peaked Ca-rich Transient with Luminous X-ray Emission and Shock-Ionized Spectral Features

Abstract

We present panchromatic observations and modeling of the Calcium-rich supernova 2019ehk in the star-forming galaxy M100 (d$\approx$16.2 Mpc) starting 10 hours after explosion and continuing for ~300 days. SN 2019ehk shows a double-peaked optical light curve peaking at $t=3$ and $15$ days. The first peak is coincident with luminous, rapidly decaying $\text{Swift}$-XRT discovered X-ray emission ($L_x\approx 10^{41}\mathrm{erg}{\mathrm{s}}^{-1}$ at 3 days; $L_x\propto t^{-3}$), and a Shane/Kast spectral detection of narrow H$\alpha$ and He II emission lines ($v\approx 500$ km/s) originating from pre-existent circumstellar material. We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at $r<10^{15}$ cm and the resulting cooling emission. We calculate a total CSM mass of $\sim$ $7\times 10^{-3}$ ${\mathrm{M}}_{\odot }$ with particle density $n\approx 10^9\mathrm{c}{\mathrm{m}}^{-3}$. Radio observations indicate a significantly lower density $n<10^4\mathrm{c}{\mathrm{m}}^{-3}$ at larger radii. The photometric and spectroscopic properties during the second light curve peak are consistent with those of Ca-rich transients (rise-time of $t_r=13.4\pm 0.210$ days and a peak B-band magnitude of $M_B=-15.1\pm 0.200$ mag). We find that SN 2019ehk synthesized $(3.1\pm 0.11)\times 10^{-2}{\mathrm{M}}_{\odot }$ of ${}^{56}\text{Ni}$ and ejected $M_{\mathrm{ej}}=(0.72\pm 0.040){\mathrm{M}}_{\odot }$ total with a kinetic energy $E_{\mathrm{k}}=(1.8\pm 0.10)\times 10^{50}\mathrm{erg}$. Finally, deep $\text{HST}$ pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (~10 ${\mathrm{M}}_{\odot }$) in binaries that lost most of their He envelope or white dwarfs. The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD + CO WD binaries.

51 pages, 27 figures. Accepted for publication in ApJ

References in corpus (28)

• The Zwicky Transient Facility: System Overview, Performance, and First Results
• Physical Properties of Wolf-Rayet Stars
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• The Zwicky Transient Facility: Science Objectives
• Determining the Type, Redshift, and Age of a Supernova Spectrum
• Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core?
• A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind
• PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
• Time Dependent Monte Carlo Radiative Transfer Calculations For 3-Dimensional Supernova Spectra, Lightcurves, and Polarization
• From Shock Breakout to Peak and Beyond: Extensive Panchromatic Observations of the Type Ib Supernova 2008D associated with Swift X-ray Transient 080109
• SOUSA: the Swift Optical/Ultraviolet Supernova Archive
• The Broad-lined Type Ic SN 2003jd
• Analysis of Late--time Light Curves of Type IIb, Ib and Ic Supernovae
• Binospec: A Wide-field Imaging Spectrograph for the MMT
• Mass transfer in white dwarf-neutron star binaries
• Illuminating Massive Black Holes With White Dwarfs: Orbital Dynamics and High Energy Transients from Tidal Interactions
• Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs
• Two New Calcium-Rich Gap Transients in Group and Cluster Environments
• Evolution of Close White Dwarf Binaries
• Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve
• Connecting the progenitors, pre-explosion variability, and giant outbursts of luminous blue variables with Gaia16cfr
• ZTF 18aaqeasu (SN 2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar Mass White Dwarf
• Fe emission and ionized excess absorption in the luminous quasar 3C109 with XMM-Newton
• The progenitors of calcium-rich transients are not formed in situ
• Calcium-Rich Gap Transients: Tidal Detonations of White Dwarfs?
• Nuclear Dominated Accretion Flows in Two Dimensions. II. Ejecta dynamics and nucleosynthesis for CO and ONe white dwarfs
• iPTF15eqv: Multi-wavelength Exposé of a Peculiar Calcium-rich Transient
• A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds. II. A Second Year of Discoveries

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