We model Galactic populations of accreting and cooling isolated neutron stars in the attempt to explore their link with a new class of dim soft X-ray sources revealed by ROSAT. For accretors we follow the magnetorotational and dynamical evolution in the Galactic potential and a realistic large scale distribution of the interstellar medium is used. Under standard assumptions old neutron stars en...

The frequencies of the highest-frequency kilohertz QPOs recently discovered in some sixteen neutron stars in low-mass X-ray binary systems are most likely the orbital frequencies of gas in Keplerian orbit around these neutron stars. If so, these QPOs provide tight upper bounds on the masses and radii of these neutron stars and important new constraints on the equation of state of neutron star m...

There are several supernova remnants which contain unresolved X-ray sources close to their centers, presumably radio-quiet neutron stars. To prove that these objects are indeed neutron stars, to understand the origin of their X-ray radiation, and to explain why they are radio-quiet, one should know their periods and period derivatives. We searched for pulsations of the X-ray flux from the radio...

Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, rotating neutron stars provides a direct method for measuring neutron-star properties. This technique constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this paper, we determine the number of distinct observables that can be derived from pulse profile model...

The energetics, spectrum, and composition of cosmic rays with energies below D1015 eV are fairly well explained by models involving supernova shocks. In contrast, no widely accepted theory exists for the origin of ultraÈhigh-energy cosmic rays (UHECRs), which have energies above 1015 eV. Instead of proposing a speciÐc model, here we place strong constraints on any model of UHECRs involving isol...

The recent discovery of high frequency oscillations in giant flares from SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. Using timing data from RHESSI, we have confirmed the detect...

It is usually proposed that hyperaccretion disks surrounding stellar-mass black holes at an accretion rate of a fraction of one solar mass per second, which are produced during the mergers of double compact stars or the collapses of massive stars, are central engines of gamma-ray bursts (GRBs). In some origin/afterglow models, however, newborn compact objects are invoked to be neutron stars rat...

We investigate the statistical evolution of magnetic neutron stars recycled in Low Mass Binary (LMB) systems, simulating synthetic populations. Irrespective to the details of the physical models, we find to be significant the fraction of neutron stars spinning close to their mass shedding limit relative to the millisecond pulsar population. The simulated neutron stars show a tail in their perio...

Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations demonstrate that the earliest generations of stars in the Galaxy, responsible for neutron-capture synthesis and the progenitors of the halo stars, were rapidly evolving. Abundance comparisons among several halo stars show that the h...

A newly discovered instability in rotating neutron stars, driven by gravitational radiation reaction acting on the starsÏ r-modes, is shown here to set an upper limit on the spin rate of young neutron stars. We calculate the timescales for the growth of linear perturbations due to gravitational radiation reaction, and for dissipation by shear and bulk viscosity, working to second order in a slo...