A. González-Galán, E. Kuulkers, P. Kretschmar, S. Larsson, K. Postnov, A. Kochetkova, M. H. Finger
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/WFC,
INTEGRAL/ISGRI and Fermi/GBM observations have been combined with previously
published data from four decades of observations. During the 1970's GX 1+4 was
spinning up with the fastest rate among the known X-ray pulsars at the time. In
the mid 1980's it underwent a change during a period of low X-ray flux 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.
View original:
http://arxiv.org/abs/1105.1907
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