Possible formation of lowly luminous highly magnetized white dwarfs by accretion leading to SGRs/AXPs

TL;DR

This paper proposes that highly magnetized, low-luminosity white dwarfs formed through accretion could explain phenomena like SGRs/AXPs and over-luminous supernovae, offering an alternative to neutron star models.

Contribution

It introduces a new evolutionary scenario for forming highly magnetized white dwarfs via accretion, potentially explaining several high-energy astrophysical phenomena.

Findings

Strong magnetic fields reduce white dwarf luminosity below detection limits.

Repeated accretion cycles can produce highly magnetized white dwarfs.

Spinning highly magnetized white dwarfs could emit gravitational waves and gamma-ray bursts.

Abstract

We sketch a possible evolutionary scenario by which a highly magnetized super-Chandrasekhar white dwarf could be formed by accretion on to a commonly observed magnetized white dwarf. This is an exploratory study, when the physics in cataclysmic variables (CVs) is very rich and complex. Based on this, we also explore the possibility that the white dwarf pulsar AR Sco acquired its high spin and magnetic field due to repeated episodes of accretion and spin-down. We show that strong magnetic field dramatically decreases luminosity of highly magnetized white dwarf (B-WD), letting them below the current detection limit. The repetition of this cycle can eventually lead to a B-WD, recently postulated to be the reason for over-luminous type Ia supernovae. A spinning B-WD could also be an ideal source for continuous gravitational radiation and soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs). SGRs/AXPs are generally believed to be highly magnetized, but observationally not confirmed yet, neutron stars. Invoking B-WDs does not require the magnetic field to be as high as for neutron star based model, however reproducing other observed properties intact.