%0 Journal Article
%T Spin period evolution of the X-ray pulsar GX 1+4
%A A. Gonz¨˘lez-Gal¨˘n
%A E. Kuulkers
%A P. Kretschmar
%A S. Larsson
%A K. Postnov
%A A. Kochetkova
%A M. H. Finger
%J Physics
%D 2012
%I arXiv
%X 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.
%U http://arxiv.org/abs/1201.1744v1