SN2019dge: A Helium-rich Ultra-stripped Envelope Supernova
Yuhan Yao, Kishalay De, Mansi M. Kasliwal, Anna Y. Q. Ho, Steve Schulze, Zhihui Li, S. R. Kulkarni, Andrew Fruchter, David Rubin, Daniel A. Perley, Jim Fuller, Anthony L. Piro, C. Fremling, Eric C. Bellm, Rick Burruss, Dmitry A. Duev, Michael Feeney, Avishay Gal-Yam, V. Zach Golkhou, Matthew J. Graham, George Helou, Thomas Kupfer, Russ R. Laher, Frank J. Masci, Adam A. Miller, Ben Rusholme, David L. Shupe, Roger Smith, Jesper Sollerman, Maayane T. Soumagnac, Jeffry Zolkower
Abstract
Abstract We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.33 M ⊙ ) and low kinetic energy (≈1.3 × 10 50 erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ∼0.1 M ⊙ located ∼1.2 × 10 13 cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from ≳5 × 10 13 cm to ≳2 × 10 16 cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400–8200 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>Gpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> (i.e., 2%–12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.