Soft gamma-ray repeaters and anomalous X-ray pulsars as highly magnetized white dwarfs

TL;DR

This paper proposes that soft gamma-ray repeaters and anomalous X-ray pulsars can be explained as highly magnetized white dwarfs, offering an alternative to magnetar models with specific observational and theoretical advantages.

Contribution

It introduces the B-WD model for SGRs/AXPs, detailing their parameter space and explaining their energies without extreme magnetic fields or additional energy sources.

Findings

B-WDs can account for SGRs/AXPs energies as rotationally powered.

B-WDs explain radio transient GCRT J1745-3009 as a white dwarf pulsar.

B-WDs follow Chandrasekhar's mass-radius relation, avoiding extreme magnetic fields.

Abstract

We explore the possibility that soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are powered by highly magnetized white dwarfs (B-WDs). We take a sample of SGRs and AXPs and provide the possible parameter space in mass, radius, and surface magnetic field based on their observed properties (period and its derivative) and the assumption that these sources obey the mass-radius relation derived for the B-WDs. The radius and magnetic field of B-WDs are adequate to explain energies in SGRs/AXPs as the rotationally powered energy. In addition, B-WDs also adequately explain the perplexing radio transient GCRT J1745-3009 as a white dwarf pulsar. Note that the radius and magnetic fields of B-WDs are neither extreme (unlike of highly magnetized neutron stars) nor ordinary (unlike of magnetized white dwarfs, yet following the Chandrasekhar's mass-radius relation (C-WDs)). In order to explain SGRs/AXPs, while the highly magnetized neutron stars require an extra, observationally not well established yet, source of energy, the C-WDs predict large ultra-violet luminosity which is observationally constrained from a strict upper limit. Finally, we provide a set of basic differences between the magnetar and B-WD hypotheses for SGRs/AXPs.