Magnetars: fact or fiction?

TL;DR

This paper critically examines the magnetar model for AXPs and SGRs, discussing observational challenges and considering alternative explanations like quark stars or fallback disks.

Contribution

It provides a comprehensive review of evidence for and against the magnetar model and explores alternative theories for these enigmatic objects.

Findings

Magnetar model faces significant observational challenges.

Alternative models include quark stars and fallback disk systems.

The nature of AXPs and SGRs remains uncertain.

Abstract

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are enigmatic pulsar-like objects. The energy budget is the fundamental problem in their studies. In the magnetar model, they are supposed to be powered by the extremely strong magnetic fields (>~ 10^14 G) of neutron stars. Observations for and against the magnetar model are both summarized. Considering the difficulties encountered by the magnetar model to comfortably understand more and more observations, one may doubt that AXPs and SGRs are really magnetars. If they are not magnetar candidates (including magnetar-based models), then they must be "quark star/fallback disk" systems.