Instability in supernova fallback disks and its effect on the formation of ultra long period pulsars

TL;DR

This paper investigates how thermal viscous instability in supernova fallback disks influences the evolution and formation of ultra long period pulsars, revealing their magnetic alignment and potential to remain active.

Contribution

It introduces a simulation of magnetar evolution considering disk instability, highlighting its role in ULPP formation and magnetic alignment patterns.

Findings

Disk instability impacts ULPP formation

ULPPs tend to be aligned or orthogonal rotators

Some ULPPs may remain above the pulsar death line

Abstract

Several pulsars with unusually long periods were discovered recently, comprising a potential population of ultra long period pulsars (ULPPs). The origin of their long periodicity is not well understood, but may be related to magnatars spun down by surrounding fallback disks. While there are few systematic investigations on the fallback disk-assisted evolution of magnetars, the instability in the disk has received little attention, which determines the lifetime of the disk. In this work we simulate the evolution of the magnetic field, spin period, and magnetic inclination angle of magnetars with a supernova fallback disk. We find that thermal viscous instability in the disk could significantly affect the formation of ULPPs. Our simulation results also reveal that a large fraction of ULPPs seem to be nearly aligned and orthogonal rotators. This might help place ULPPs above the death line in the pulse period - period derivative plane. However, some extra mechanisms seem to be required to account for radio emission of ULPPs.