SAX J2103.5+4545 has been continuously monitored for ∼900 d by the Rossi X‐ray Timing Explorer (RXTE) since its outburst in 2002 July. Using these observations and previous archival RXTE observations of SAX J2103.5+4545, we refined the binary orbital parameters and find the new orbital period as P= (12.665 36 ± 0.000 88) d and the eccentricity as 0.4055 ± 0.0032. With these new orbital parameters, we constructed the pulse frequency and pulse frequency derivative histories of the pulsar and confirmed the correlation between X‐ray flux and pulse frequency derivative presented by Baykal, Stark & Swank. We constructed the power spectra for the fluctuations of pulse frequency derivatives and found that the power‐law index of the noise spectra is 2.13 ± 0.6. The power‐law index is consistent with random walk in pulse frequency derivative and is the steepest among the HMXRBs. X‐ray spectra analysis confirmed the inverse correlation trend between power‐law index and X‐ray flux found by Baykal et al.

XMM-Newton observed SAX J2103.5+4545 on 2003 January 6, while the Rossi X-Ray Timing Explorer (RXTE ) was also monitoring the source. Using the RXTE Proportional Counter Array data set between 2002 December 3 and 2003 January 29, the spin period and average spin-up rate during the XMM-Newton observations were found to be 354:7940 AE 0:0008 s and (7:4 AE 0:9) ; 10 À13 Hz s À1 , respectively. In the power spectrum of the 0.9-11 keV EPIC PN light curve, we found quasi-periodic oscillations (QPOs) around 0.044 Hz (22.7 s) with an rms fractional amplitude of $6.6%. We interpreted this QPO feature as the Keplerian motion of inhomogeneities through the inner disk. In the X-ray spectrum, in addition to the power-law component with high-energy cutoff and the $6.4 keV fluorescent iron emission line, we discovered a soft component consistent with blackbody emission with kT $ 1:9 keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius of $0.3 km, suggesting the polar cap on the neutron star surface as the source of the blackbody emission. The flux of the iron emission line at $6.42 keV was shown to peak at the off-pulse phase, supporting the idea that this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap.

We present timing and spectral analysis of RXTE‐PCA (Proportional Counter Array) observations of the accretion powered pulsar 4U 1907+09 between 2007 June and 2008 August. 4U 1907+09 had been in a spin‐down episode with a spin‐down rate of −3.54 × 10−14 Hz s−1 before 1999. From RXTE observations after 2001 March, the source showed a ∼60 per cent decrease in spin‐down magnitude, and INTEGRAL observations after 2003 March showed that source started to spin‐up. We found that the source recently entered into a new spin‐down episode with a spin‐down rate of −3.59 × 10−14 Hz s−1. This spin‐down rate is pretty close to the previous long‐term spin‐down rate of the source measured before 1999. From the spectral analysis, we showed that hydrogen column density varies with the orbital phase.

We analysed RXTE archival observations of 4U 1907+09 between 1996 February 17 and 2002 March 6. The pulse timing analysis showed that the source stayed at almost constant period around 1998 August and then started to spin-down at a rate of (−1.887 ∓ 0.042) × 10 −14 Hz s −1 which is ∼0.60 times lower than the long-term (∼15 yr) spin-down rate. Our pulsefrequency measurements for the first time resolved significant spin-down rate variations since the discovery of the source. We also presented orbital phase resolved X-ray spectra during two stable spin-down episodes during March. The source has been known to have two orbitally locked flares. We found that X-ray flux and spectral parameters except hydrogen column density agreed with each other during the flares. We interpreted the similar values of X-ray fluxes as an indication of the fact that the source accretes not only via transient retrograde accretion disc but also via the stellar wind of the companion, so that the variation of the accretion rate from the disc does not cause significant variation in the observed X-ray flux. Lack of significant change in spectral parameters except hydrogen column density was interpreted as a sign of the fact that the change in the spin-down rate of the source was not accompanied by a significant variation in the accretion geometry.

We present analysis of RXTE-PCA observations of GX 1+4 between March 3, 2001 and January 31, 2003 together with the CGRO-BATSE Xray flux and frequency derivative time series between 1991 and 1999. From the timing analysis of RXTE-PCA observations, we are able to phase connect pulse arrival times of the source within two different time intervals and obtain corresponding timing solutions. Using these pulse arrival times, we contribute to long term pulse frequency history of the source. We look for episodic correlations and anti-correlations between torque and X-ray luminosity using CGRO-BATSE X-ray flux and frequency derivative time series and find that correlation state of GX 1+4 seems to change on ∼ 100-200 days long intervals. We estimate torque noise of the source and observe flickering noise ( f −1 ). We achieve to measure the longest observed timescale for a noise process among accretion powered X-ray pulsars by extending the noise estimate for a time scale ranging from 31 days to 44 years. Spectral analysis of individual RXTE-PCA observations indicates a significant correlation between iron line flux and unabsorbed X-ray flux. Pulse phase resolved spectra of the source indicate a broadening of iron line complex at the bin corresponding to the pulse minimum.

The high mass X-ray binary pulsar 4U 1538-52 was observed between July 31 and August 7, 2003. Using these observations, we determined new orbital epochs for both circular and elliptical orbit models. The orbital epochs for both orbit solutions agreed with each other and yielded an orbital period derivativeṖ/P = (0.4 ± 1.8) × 10 −6 yr −1 . This value is consistent with the earlier measurement ofṖ/P = (2.9 ± 2.1) × 10 −6 yr −1 at the 1σ level and gives only an upper limit to the orbital period decay. Our determination of the pulse frequency showed that the source spun up at an average rate of 2.76 × 10 −14 Hz s −1 between 1991 and 2003.

We present the discovery of the orbital period of Swift J1626.6−5156. Since its discovery in 2005, the source has been monitored with Rossi X-Ray Timing Explorer, especially during the early stage of the outburst and into the X-ray modulating episode. Using a data span of ∼700 days, we obtain the orbital period of the system as 132.9 days. We find that the orbit is close to a circular shape with an eccentricity 0.08, that is one of the smallest among Be/X-ray binary systems. Moreover, we find that the timescale of the X-ray modulations varied, which led to earlier suggestions of orbital periods at about a third and half of the orbital period of Swift J1626.6−5156.

We present timing analysis of the accretion powered pulsar SXP 1062, based on the observations of Swift, XMM-Newton and Chandra satellites covering a time span of about 2 years. We obtain a phase coherent timing solution which shows that SXP 1062 has been steadily spinning down with a rate − 4.29(7) × 10 −14 Hz s −1 leading to a surface magnetic field estimate of about 1.5 × 10 14 G. We also resolve the binary orbital motion of the system from X-ray data which confirms an orbital period of 656(2) days. On MJD 56834.5, a sudden change in pulse frequency occurs with ∆ν = 1.28(5) × 10 −6 Hz, which indicates a glitch event. The fractional size of the glitch is ∆ν/ν ∼ 1.37(6) ×10 −3 and SXP 1062 continues to spin-down with a steady rate after the glitch. A short X-ray outburst 25 days prior to the glitch does not alter the spin-down of the source; therefore the glitch should be associated with the internal structure of the neutron star. While glitch events are common for isolated pulsars, the glitch of SXP 1062 is the first confirmation of the observability of this type of events among accretion powered pulsars. Furthermore, the value of the fractional change of pulse frequency ensures that we discover the largest glitch reported up to now.