S. Sahiner, S. C. Inam, A. Baykal
We analyse \emph{INTEGRAL} (between 2005 October and 2007 November) and
\emph{RXTE} (between 2007 June and 2011 March) observations of the accretion
powered pulsar 4U 1907+09. From \emph{INTEGRAL} IBIS-ISGRI and \emph{RXTE}-PCA
observations, we update pulse period history of the source. We construct power
spectrum density of pulse frequencies and find that fluctuations in the pulse
frequency derivatives are consistent with the random walk model with a noise
strength of $1.27\times10^{-21}$ Hz s$^{-2}$. From the X-ray spectral analysis
of \emph{RXTE}-PCA observations, we find that Hydrogen column density is
variable over the binary orbit, tending to increase just after the periastron
passage. We also show that the X-ray spectrum gets hardened with decreasing
X-ray flux. We discuss pulse-to-pulse variability of the source near dipping
ingress and egress. We find that the source more likely undergoes in dipping
states after apastron until periastron when the accretion from clumpy wind
might dominate so that occasional transitions to temporary propeller state
might occur.
View original:
http://arxiv.org/abs/1106.5957
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