Spin period evolution of the X-ray pulsar GX 1+4

TL;DR

This paper analyzes the long-term spin period evolution of the X-ray pulsar GX 1+4 over four decades, showing a continued spin-down trend consistent with a quasi-spherical accretion model.

Contribution

It provides new long-term observational data and interprets the spin evolution within a quasi-spherical accretion framework, extending understanding of pulsar spin dynamics.

Findings

GX 1+4's spin period increased from ~110 s to ~160 s over 30 years.

The pulsar's spin-down trend is ongoing and stronger than before.

Observations align with a quasi-spherical accretion model from the companion's stellar wind.

Abstract

We report on the long-term evolution of the spin period of the symbiotic X-ray pulsar GX 1+4 and a possible interpretation within a model of quasi-spherical accretion. New period measurements from BeppoSAX, INTEGRAL and Fermi observations have been combined with previously published data from four decades of observations. During the 1970s GX 1+4 was spinning up with the fastest rate among the known X-ray pulsars at the time. In the mid 1980s it underwent a change during a period of low X-ray ux and started to spin down with a rate similar in magnitude to the previous spin up rate. The spin period has changed from ~110 s to ~160 s within the last three decades. Our results demonstrate that the overall spin down trend continues and is stronger than ever. We compare the observations with predictions from a model assuming quasi-spherical accretion from the slow wind of the M giant companion.