Altan Baykal (Middle East Technical University, Turkey)

A Comprehensive Study on RXTE and INTEGRAL Observations of the X-ray Pulsar 4U 1907+09

We analyse INTEGRAL IBIS-ISGRI (between 2005 October and 2007 November) and RXTE-PCA (between
2007 June and 2011 March) observations of the accretion powered pulsar 4U 1907+09. From INTEGRAL
and 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
random walk model with a noise strength of 1.27\ x10^{-21} Hz sec^{-2}. From the X-ray spectral analysis of
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 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 during when the source is near apastron during which the
accretion from clumpy wind might dominate so that occasional transitions to temporary propeller state might
occur.