We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d≈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 Swift-XRT discovered X-ray emission (Lx ≈ 1041 erg s−1 at 3 days; Lx ∝ t−3), and a Shane/Kast spectral detection of narrow Hα and He ii emission lines (v ≈ 500 km s−1) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r < 1015 cm and the resulting cooling emission. We calculate a total CSM mass of ∼ 7 × 10−3 M☉ (MHe/MH ≈ 6) with particle density n ≈ 109 cm−3. Radio observations indicate a significantly lower density n < 104 cm−3 at larger radii r > (0.1 − 1) × 1017 cm. The photometric and spectroscopic properties during the second light curve peak are consistent with those of Ca-rich transients (rise-time of tr = 13.4 ± 0.210 days and a peak B-band magnitude of MB = −15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10−2 M☉ of 56Ni and ejected Mej = (0.72 ± 0.040) M total with a kinetic energy Ek = (1.8 ± 0.10) × 1050 erg. Finally, deep 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 M☉) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD + CO WD binaries.
|Original language||English (US)|
|State||Published - May 4 2020|
- Supernovae: individual (SN 2019ehk)
- White dwarfs
ASJC Scopus subject areas