Related papers: Enigmatic sub-luminous accreting neutron stars in …
We present X-ray spectra of four ultraluminous infrared galaxies (ULIRGs) with detectable broad near-infrared emission lines produced by active galactic nuclei (AGNs): Mrk 463, PKS 1345+12, IRAS 05189-2524, and IRAS 07598+6508. With the…
Both neutron stars and strange stars are capable of supporting fast rotations observed in pulsars. On the basis of this it has been argued that some of the pulsars could be strange stars. We investigate whether strange stars can sustain…
We present a new model for low-luminosity X-ray sources in globular clusters, with L_x < 10^34 erg/s. The model we propose is that of a single neutron star accreting from cluster gas that has accumulated as a natural product of stellar…
We investigate the equations of state for pure neutron matter and strange hadronic matter in $\beta$-equilibrium, including $\Lambda$, $\Sigma$ and $\Xi$ hyperons. The masses and radii of pure neutron stars and strange hadronic stars are…
The unknown state of matter at ultra-high density, large proton/neutron number asymmetry, and low temperature is a major long-standing problem in modern physics. Neutron stars provide the only known setting in the Universe where matter in…
Galactic accretion driven stellar X-ray sources can be divided into groups in different ways. An important division, which covers almost all known X-ray binaries, can be made according to the mass of the donor star: high-mass X-ray binaries…
We report on unusually very hard spectral states in three confirmed neutron-star low-mass X-ray binaries (1RXS J180408.9-342058, EXO 1745-248, and IGR J18245-2452) at a luminosity between ~ 10^{36-37} erg s^{-1}. When fitting the Swift…
Based on our long (~ 300 ks) 2007 XMM-Newton observation of the Seyfert galaxy NGC 1365, we report here on the spectral and timing behaviour of two ultraluminous X-ray sources, which had previously reached isotropic X-ray luminosities L_X ~…
We show that if the sources of ultra-high energy cosmic rays (UHECRs) with energies E>10^{19}eV are associated with galaxies, then the production of UHECRs must occur in transient events. Our galaxy is currently at a dim state in between…
Nearby galactic nuclei are observed to be very much dimmer than active galactic nuclei in distant galaxies. The Chandra X-ray Observatory has provided a definitive explanation for why this is so. With its excellent angular resolution,…
The study of the hard (E>10 keV) energy spectra of X-ray binary pulsars can give a wealth of information on the physical processes that occur close to the neutron star surface. Extreme matter regimes are probed, and precious information on…
The fluctuating brightness of cosmic X-ray sources, particularly accreting black holes and neutron star systems, has enabled enormous progress in understanding the physics of turbulent accretion flows, the behaviour of matter on the…
We fit hydrogen atmosphere models to the X-ray data for four neutron stars (three from a previous paper, plus 4U 2129+47) and six black hole candidates (A0620-00, GS 2000+25, GS 1124-68, GS 2023+33, GRO J1655-40, and GRO J0422+32). While…
We highlight recent theoretical and observational progress in several areas of neutron star astrophysics, and discuss the prospect for advances in the next decade.
We present recent work on using astronomical observations of neutron stars to reveal unique insights into nuclear matter that cannot be obtained from laboratories on Earth. First, we discuss our measurement of the rapid cooling of the…
We find constraints on minimum and maximum mass of ordinary neutron stars imposed by their early evolution (protoneutron star stage). We calculate models of protoneutron stars using a realistic standard equation of state of hot, dense…
Possible manifestations of accreting magnetars are discussed. It is shown that the four ultra-luminous X-ray pulsars can be understood in the accreting low magnetic field magnetar scenario. The NGC300 ULX1 pulsar may have a higher dipole…
Transiently accreting neutron stars in quiescence (Lx<10^34 erg/s) have been observed to vary in intensity by factors of few, over timescales of days to years. If the quiescent luminosity is powered by a hot NS core, the core cooling…
We have observed the nucleus of the nearby luminous infrared galaxy NGC 4418 with subarcsec resolution at 860 and 450 micron for the first time to characterize its hidden power source. A ~20 pc (0.1") hot dusty core was found inside a 100…
We report here on the results of the analysis of Chandra, XMM-Newton and NuSTAR recent observations of the Supergiant Fast X-ray Transient XTEJ1739-302. The source was caught in a low X-ray luminosity state, from a few $10^{31}$ to…