AXPs & SGRs: Magnetar or Quarctar?

TL;DR

This paper challenges the magnetar model for AXPs and SGRs, proposing a new 'quarctar' model involving crusted quark stars in accretion disks to better explain observations and address previous inconsistencies.

Contribution

It introduces the 'quarctar' model as an alternative to magnetars, accounting for X-ray luminosity and radio emissions without requiring super strong magnetic fields.

Findings

Magnetic field estimates via the normal method are likely incorrect due to wind braking.

The quarctar model naturally explains X-ray emissions, burst luminosity, and spectra.

Radio-emitting AXPs are also consistent with the quarctar hypothesis.

Abstract

The concept of a "magnetar" was proposed mainly because of two factors. First, the X-ray luminosity of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters (SGRs) is larger than the rotational energy loss rate, and second, the magnetic field strength calculated from "normal method" is super strong. It is proposed that the radiation energy of magnetar comes from its magnetic fields. Here it is argued that the magnetic field strength calculated through the normal method is incorrect when X-ray luminosity is larger than rotational energy loss rate, because the wind braking is not taken into account. Besides, the "anti-magnetar" and some other X-ray and radio observations are difficult to understand with a magnetar model. Instead of the magnetar, we propose a "quarctar", which is a crusted quark star in an accretion disk, to explain the observations. In this model, the persistent X-ray emission, burst luminosity, spectrum of AXPs and SGRs can be understood naturally. The radio-emitting AXPs, which are challenging the magnetar, can also be explained by the quarctar model.