SN2019dge: A Helium-rich Ultra-stripped Envelope Supernova

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 e) 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 e 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-Gpc yr 3 1 (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.

A Diversity of Wave-driven Presupernova Outbursts

“…In hydrogen-free progenitors, the ejected mass would form a dense wind (Fuller & Ro 2018) of circumstellar He, perhaps similar to that observed via flash ionization in the heavily stripped Type Ib/c SNe iPTF 14gqr (De et al 2019) and SN 2019dge (Yao et al 2020). However, SNe with even larger inferred CSM radii (R CSM 10 17 cm, such as SN 2004dk (Mauerhan et al 2018;Pooley et al 2019), most likely arise from a different mechanism that can operate at longer timescales (100 yr) before core collapse.…”

“…Recent examples of SNe with evidence for early interaction include Type II SNe such as SN 2016bkv (Nakaoka et al 2018), SN 2018zd (Zhang et al 2020), and many others (Khazov et al 2016;Förster et al 2018), and Type I SNe such as LSQ 13abf (Stritzinger et al 2020), LSQ 13ddu (Clark et al 2020), SN 2018bgv and SN 2018don (Lunnan et al 2020), SN 2018gep (Ho et al 2019), SN 2019dge (Yao et al 2020), and SN 2019uo (Gangopadhyay et al 2020). These SNe extend across virtually all spectroscopic classes of SNe (including Type II-P, II-L, IIn, Ib, Ic, Ibn, Ic-BL, superluminous Ic, etc.).…”

A WC/WO star exploding within an expanding carbon–oxygen–neon nebula

“…We compare our X-ray data to similar observations of other RETs. We use a recently presented sample 82 and augment it with observations of CSS161010 83 , iPTF14gqr 84 , SN 2019dge 137 , SN 2018gep 85 and AT2020xnd (ZTF20acigmel) 86 . All Swift XRT data are analyzed as detailed above, while Chandra observations of CSS161010 are converted to the same scale assuming a power law spectrum with index 2.…”

Shock Cooling Emission from Extended Material Revisited

“…SN 2019dge was a helium-rich SN with a fast-evolving light curve indicating a low ejecta mass (Yao et al 2020). Its early rise was too rapid to be explained as radioactively powered diffusion and was thus interpreted as being due to SCE from extended material.…”

“…More recently, similar structures involving extended material have been invoked to explain a wide variety of transient events (e.g., De et al 2018a;Taddia et al 2018;Fremling et al 2019;Ho et al 2020;Jacobson-Galán et al 2020;Yao et al 2020). Constraining the mass and radius of extended material usually involves comparing the observations to rough analytic scalings or fitting semianalytic models (Nakar & Piro 2014;Piro 2015;Nagy & Vinkó 2016;Sapir & Waxman 2017).…”