X-rays observations of a super-Chandrasekhar object reveal an ONeMg and a CO white dwarf merger product embedded in a putative SN Iax remnant

TL;DR

This study presents the first X-ray observations of a white dwarf merger product, IRAS 00500+6713, revealing its composition, merger history, and potential link to a supernova Iax, indicating a super-Chandrasekhar mass origin.

Contribution

It provides new X-ray spectroscopic data on a WD merger product, supporting its origin from an ONe and CO white dwarf merger and suggesting a connection to supernova Iax events.

Findings

Detection of X-ray emission from the merger product and nebula.

Evidence of neon, magnesium, silicon, and sulfur enrichment.

Indications of a super-Chandrasekhar mass and possible SN Iax association.

Abstract

The merger of two white dwarfs (WD) is a natural outcome from the evolution of many binary stars. Recently, a WD merger product, IRAS 00500+6713, was identified. IRAS 00500+6713 consists of a central star embedded in a circular nebula. The analysis of the optical spectrum of the central star revealed that it is hot, hydrogen and helium free, and drives an extremely fast wind with a record breaking speed. The nebula is visible in infrared and in the [O III] line images. No nebula spectroscopy was obtained prior to our observations. Here we report the first deep X-ray imaging spectroscopic observations of IRAS 00500+6713. Both the central star and the nebula are detected in X-rays, heralding the WD merger products as a new distinct type of strong X-ray sources. Low-resolution X-ray spectra reveal large neon, magnesium, silicon, and sulfur enrichment of the central star and the nebula. We conclude that IRAS 00500+6713 resulted from a merger of an ONe and a CO WD, which supports earlier suggestion for a super-Chandrasekhar mass of this object. X-ray analysis indicates that the merger was associated with an episode of carbon burning and possibly accompanied by a SN Iax. In X-rays, we observe the point source associated with the merger product while the surrounding diffuse nebula is a supernova remnant. IRAS 00500+6713 will likely terminate its evolution with another peculiar Type I supernova, where the final core collapse to a neutron star might be induced by electron captures.