We have computed an extensive grid of binary evolution tracks to represent low-and intermediate mass X-ray binaries (LMXBs and IMXBs). The grid includes 42,000 models which covers 60 initial donor masses over the range of 1 − 4 M ⊙ and, for each of these, 700 initial orbital periods over the range of 10 − 250 hours. These results can be applied to understanding LMXBs and IMXBs: those that evolve analogously to CVs; that form ultracompact binaries with P orb in the range of 6 − 50 minutes; and that lead to wide orbits with giant donors. We also investigate the relic binary recycled radio pulsars into which these systems evolve. To evolve the donor stars in this study, we utilized a newly developed stellar evolution code called "MESA" that was designed, among other things, to be able to handle very low-mass and degenerate donors. This first application of the results is aimed at an understanding of the newly discovered pulsar PSR J1614-2230 which has a 1.97 M ⊙ neutron star, P orb = 8.7 days, and a companion star of 0.5 M ⊙ . We show that (i) this system is a cousin to the LMXB Cyg X-2; (ii) for neutron stars of canonical birth mass 1.4 M ⊙ , the initial donor stars which produce the closest relatives to PSR J1614-2230 have a mass between 3.4 − 3.8 M ⊙ ; (iii) neutron stars as massive as 1.97 M ⊙ are not easy to produce in spite of the initially high mass of the donor star, unless they were already born as relatively massive neutron stars; (iv) to successfully produce a system like PSR J1614-2230 requires a minimum initial neutron star mass of at least 1.6 ± 0.1 M ⊙ , as well as initial donor masses and P orb of ∼4.25 ± 0.10 M ⊙ and ∼49 ± 2 hrs, respectively; and (v) the current companion star is largely composed of CO, but should have a surface H abundance of ∼10 − 15%.

We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748−676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional amplitude was 15% (rms). The dynamic power density spectrum for each burst revealed an increase in frequency of ≈ 1-2 Hz while the oscillation was present. The frequency drift, the high significance of the detections and the almost identical signal frequencies measured in two bursts separated by 11 months, confirms this signal as a burst oscillation similar to those found in 13 other sources to date. We thus conclude that the spin frequency in EXO 0748−676 is within a few Hz of 552 Hz, rather than 45 Hz as was suggested from an earlier signal detection by Villarreal & Strohmayer (2004). Consequently, Doppler broadening must significantly affect spectral features arising from the neutron star surface, so that the narrow absorption features previously reported from an XMM-Newton spectrum could not have arisen there. The origin of both the previously reported 45 Hz oscillation and the X-ray absorption lines is now uncertain.

Glitches are common phenomena in pulsars. After each glitch, there is often a permanent increase in the pulsar's spin-down rate. Therefore, a pulsar's present spin-down rate may be much higher than its initial value and the characteristic age of a pulsar based on its present spin-down rate and period may be shorter than its true age. At the same time, the permanent increase of its spin-down rate implies that the pulsar's surface magnetic field is increased after each glitch. Consequently, after many glitches some radio pulsars may evolve into magnetars, i.e., strongly magnetized and slowly rotating neutron stars.

It is known that some observed gamma-ray bursts (GRBs) are produced at cosmological distances and that the GRB production rate may follow the star formation rate. We model the BATSE-detected intensity distribution of long GRBs in order to determine their space density distribution and opening angle distribution. Our main results are: the lower and upper distance limits to the GRB production are z % 0:24 and >10, respectively; the GRB opening angle follows an exponential distribution and the mean opening angle is about 0.03 radians; and the peak luminosity appears to be a better standard candle than the total energy of a GRB.

X-ray observations of EXO 0748−676 during thermonuclear bursts revealed a set of narrow (∆λ/λ = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron-star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.