SGR 0418+5729: a small inclination angle resulting in a not so low dipole magnetic field?

TL;DR

This paper investigates the spin-down behavior of SGR 0418+5729, suggesting it may have a strong magnetic field and be a normal magnetar with a small inclination angle, challenging previous assumptions about its magnetic field strength.

Contribution

It applies the pulsar spin-down model to SGR 0418+5729, proposing a high magnetic field possibility due to a small inclination angle, which redefines its classification.

Findings

SGR 0418+5729 lies below the pulsar death line.

Its magnetospheric activity may have ceased.

It could have a magnetic field much higher than previously estimated.

Abstract

The spin down behaviors of SGR 0418+5729 are investigated. The pulsar spin down model of Contopoulos & Spitkovsky (2006) is applied to SGR 0418+5729. It is shown that SGR 0418+5729 lies below the pulsar death line and its rotation-powered magnetospheric activities may therefore have stopped. The compact star is now spun down by the magnetic dipole moment perpendicular to its rotation axis. Our calculations show that under these assumption there is the possibility of SGR 0418+5729 having a strong dipole magnetic field, if there is a small magnetic inclination angle. Its dipole magnetic field may be much higher than the characteristic magnetic field. Therefore, SGR 0418+5729 may be a normal magnetar instead of a low magnetic field magnetar.