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arXiv · 1111.6791

Spin period evolution of GX 1+4

A. González-Galán·E. Kuulkers·P. Kretschmar·S. Larsson·K. Postnov·A. Kochetkova·M. H. Finger
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Abstract

We aim both to complement the existing data on the spin history of the peculiar accreting X-ray pulsar GX 1+4 with more past and current data from BeppoSAX, INTEGRAL, and Fermi and to interpret the evolution in the framework of accretion theory. We used source light curves obtained from BeppoSAX/WFC and INTEGRAL/ISGRI to derive pulse periods using an epoch-folding analysis. Fermi/GBM data were analyzed by fitting a constant plus a Fourier expansion to background-subtracted rates, and maximizing the Y2 statistic. We completed the sample with hard X-ray light curves from Swift/BAT. The data were checked for correlations between flux and changes of the pulsar spin on different timescales. The spin-down of the pulsar continues with a constant change in frequency, i.e., an apparently accelerating change in the period. Over the past three decades, the pulse period has increased by about ~50%. Short-term fluctuations on top of this long-term trend do show anti-correlation with the source flux. Possible explanations of the observed long-term frequency and its dependence on flux are discussed.

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A. González-Galán, E. Kuulkers, P. Kretschmar, S. Larsson, K. Postnov, A. Kochetkova, M. H. Finger. 2012-01-11. Spin period evolution of GX 1+4. https://doi.org/10.1051/0004-6361%2F201117893

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