Thermal X-ray emission from massive, fast rotating, highly magnetized white dwarfs

TL;DR

This paper explores the potential of massive, fast-rotating, highly magnetized white dwarfs to act as pulsar-like objects emitting detectable X-ray radiation, expanding the understanding of high-energy emissions from such stars.

Contribution

It introduces the concept of WD pulsars with specific structure parameters and predicts their X-ray emission, linking observed phenomena like soft gamma-repeaters to white dwarf models.

Findings

White dwarfs above the death-line can emit soft X-ray blackbody radiation.

Magnetic polar cap heating by pair-created particles explains X-ray emissions.

The model connects WD properties to observed high-energy astrophysical phenomena.

Abstract

There is solid observational evidence on the existence of massive, $M\sim 1~M_\odot$, highly magnetized white dwarfs (WDs) with surface magnetic fields up to $B\sim 10^9$ G. We show that, if in addition to these features, the star is fast rotating, it can become a rotation-powered pulsar-like WD and emit detectable high-energy radiation. We infer the values of the structure parameters (mass, radius, moment of inertia), magnetic field, rotation period and spin-down rates of a WD pulsar death-line. We show that WDs above the death-line emit blackbody radiation in the soft X-ray band via the magnetic polar cap heating by back flowing pair-created particle bombardment and discuss as an example the X-ray emission of soft gamma-repeaters and anomalous X-ray pulsars within the WD model.