A. González-Galán, E. Kuulkers, P. Kretschmar, S. Larsson, K. Postnov, A. Kochetkova, M. H. Finger
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.
View original:
http://arxiv.org/abs/1111.6791
No comments:
Post a Comment