The superslow pulsation X-ray pulsars in high mass X-ray binaries

TL;DR

This paper investigates a rare class of high mass X-ray binary pulsars with extremely slow spin periods, analyzing their temporal and spectral properties, and discussing their possible origins and evolution channels, including the magnetar hypothesis.

Contribution

It provides detailed long-term observational analysis of superslow pulsation X-ray pulsars and explores their potential as young systems or accreting magnetars, challenging standard binary evolution models.

Findings

Observed spin period evolution in two sources over 20 years.

Identified the need for strong magnetic fields (>10^{14} G) to explain superslow periods.

Discussed possible origins including young systems and accreting magnetars.

Abstract

There exists a special class of X-ray pulsars that exhibit very slow pulsation of $P_{\rm spin}>1000$ s in the high mass X-ray binaries (HMXBs). We have studied the temporal and spectral properties of these superslow pulsation neutron star binaries in hard X-ray bands with INTEGRAL observations. Long-term monitoring observations find spin period evolution of two sources: spin-down trend for 4U 2206+54 ($P_{\rm spin}\sim 5560$ s with $\dot{P}_{\rm spin}\sim 4.9\times 10^{-7}$ s s$^{-1}$) and long-term spin-up trend for 2S 0114+65 ($P_{\rm spin}\sim 9600$ s with $\dot{P}_{\rm spin}\sim -1\times 10^{-6}$ s s$^{-1}$) in the last 20 years. A Be X-ray transient, SXP 1062 ($P_{\rm spin}\sim 1062$ s), also showed a fast spin-down rate of $\dot{P}_{\rm spin}\sim 3\times 10^{-6}$ s s$^{-1}$ during an outburst. These superslow pulsation neutron stars cannot be produced in the standard X-ray binary evolution model unless the neutron star has a much stronger surface magnetic field ($B>10^{14}$ G). The physical origin of the superslow spin period is still unclear. The possible origin and evolution channels of the superslow pulsation X-ray pulsars are discussed. Superslow pulsation X-ray pulsars could be younger X-ray binary systems, still in the fast evolution phase preceding the final equilibrium state. Alternatively, they could be a new class of neutron star system $-$ accreting magnetars.