A Comprehensive Study on RXTE & INTEGRAL Observations of the X-ray   Pulsar 4U 1907+09
  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. 
S. Sahiner (1), S.C. Inam (2), A. Baykal (1) ((1) METU, Ankara,   Turkey, (2) Baskent University, Ankara, Turkey)
astro-ph.HE