We have detected a transient X-ray source in the M31 bulge through a continuing monitoring campaign with the Chandra ACIS-I camera. The source was detected at R.A.=00:42:33.428± 0.11, Dec.=+41:17:03.37 ± 0.11 in only a single observation taken 2004-May-23. Fortuitous optical HST/ACS imaging of the transient location prior to the X-ray outburst, along with follow-up HST/ACS imaging during and af...

Using the 9 years of continuous data now available from the Burst And Transient Source Experiment (BATSE) aboard CGRO, we have measured orbital periods and produced folded lightcurves for 8 High Mass X-ray Binaries (HMXB). Given the length of the datasets, our determinations are based on many more binary orbits than previous investigations. Thus our source detections have high statistical signi...

We present an analytical method for studying the changes of the orbital characteristics of binary systems with circular orbits due to a kick velocity imparted to the newborn neutron star during a supernova explosion (SN). Assuming a Maxwellian distribution of kick velocities we derive analytical expressions for the distribution functions of orbital separations and eccentricities immediately aft...

We report on the implications of the peak in the cosmic star-formation rate (SFR) at redshift z ≈ 1.5 for the resulting population of low-mass X-ray binaries(LMXB) and for that of their descendants, the millisecond radio pulsars (MRP). Since the evolutionary timescales of LMXBs, their progenitors, and their descendants are thought be significant fractions of the time-interval between the SFR pe...

Fifteen Be/X-ray binaries and candidates in the SMC were observed serendipitously with the EPIC instruments of XMM-Newton during two observations of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those sources are detected. For eleven of them an accurate position and in part detection of X-ray pulsations support the proposed identification as Be/X-ray binaries. In one cas...

In a high-mass X-ray binary (HMXB) a massive star interacts with a neutron-star or black-hole companion in various ways. The gravitational interaction enables the measurement of fundamental parameters such as the mass of both binary components, providing important constraints on the evolutionary history of the system, the equation of state of matter at supra-nuclear density, and the supernova m...

We report on Rossi X-ray Timing Explorer observations of four type I X-ray bursters; namely 1E1724– 3045, GS1826–238, SLX1735–269 and KS1731-260. The first three were in a low state, with 1-200 keV Xray luminosities in the range ∼ 0.05−0.1 LEdd (LEdd: Eddington luminosity for a neutron star = 2.5×10 38 ergs s), whereas KS1731-260 was in a high state with a luminosity ∼ 0.35 LEdd. The low state ...

It has long been known that X-ray and optical/UV variability in active X-ray binaries is sometimes correlated. The expectation has been that this arises from rapid reprocessing of X-rays into longer wavelength photons, and hence that the lags between the bandpasses can be used to reconstruct an echomap of the binary, revealing the geometry and spatial scale of reprocessing sites. I will review ...

Kilohertz quasi-periodic oscillations (kHz QPOs) has been regarded as representing the Keplerian frequency at the inner disk edge in the neutron star X-ray binaries. The so-called “parallel tracks” on the plot of the kHz QPO frequency vs. X-ray flux in neutron star Xray binaries, on the other hand, show the correlation between the kHz QPO frequency and the X-ray flux on time scales from hours t...