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The X-ray spectra of some magnetized isolated neutron stars (NSs) show absorption features with equivalent widths (EWs) of 50 - 200 eV, whose nature is not yet well known. To explain the prominent absorption features in the soft X-ray spectra of the highly magnetized (B ~ 1014 G) X-ray dim isolated NSs (XDINSs), we theoretically investigate different NS local surface models, including naked condensed iron surfaces and partially ionized hydrogen model atmospheres, with semi-infinite and thin atmospheres above the condensed surface. We also developed a code for computing light curves and integral emergent spectra of magnetized neutron stars with various temperature and magnetic field distributions over the NS surface. We compare the general properties of the computed and observed light curves and integral spectra for XDINS RBS 1223 and conclude that the observations can be explained by a thin hydrogen atmosphere above the condensed iron surface, while the presence of a strong toroidal magnetic field component on the XDINS surface is unlikely. We suggest that the harmonically spaced absorption features in the soft X-ray spectrum of the central compact object (CCO) 1E 1207.4-5209 (hereafter 1E 1207) correspond to peaks in the energy dependence of the free-free opacity in a quantizing magnetic field, known as quantum oscillations. To explore observable properties of these quantum oscillations, we calculate models of hydrogen NS atmospheres with B ~ 1010-1011 G (i.e., electron cyclotron energy Ec,e ~ 0.1-1 keV) and Teff = 1-3 MK. Such conditions are thought to be typical for 1E 1207. We show that observable features at the electron cyclotron harmonics with EWs 100 - 200 eV can arise due to these quantum oscillations. [ABSTRACT FROM AUTHOR]

Pulsars are known to be efficient accelerators that produce copious amounts of relativistic particles and inject them into the Galactic medium. The radiation emitted by such a pulsar wind can be seen from radio through γ-rays as a pulsar-wind nebula (PWN). Here we overview and summarize recent progress in X-ray and TeV observations of PWNe. [ABSTRACT FROM AUTHOR]

Pulsar winds shocked in the ambient medium produce spectacular nebulae observable from the radio through γ-rays. The shape and the spectrum of a pulsar wind nebula (PWN) depend on the angular distribution, magnetization and energy spectrum of the wind streaming from the pulsar magnetosphere, as well as on the pulsar velocity and the properties of the ambient medium. The advent of Chandra, with its unprecedented angular resolution and high sensitivity, has allowed us not only to detect many new PWNe, but also study their spatial and spectral structure and dynamics, which has significantly advanced our understanding of these objects. Here we overview recent observational results on PWNe, with emphasis on Chandra observations. [ABSTRACT FROM AUTHOR]

The isolated neutron star (INS) RX J1308.6+2127 has been observed with Chandra and XMM-Newton several times between 2000 and 2007. The six most recent XMM-Newton observations are part of a monitoring campaign we initiated to study the long-term temporal and spectral properties of INSs. The primary goal of this investigation is to better quantify the similarities and differences between INSs and magnetar candidates (i.e. Anomalous X-ray Pulsars and Soft Gamma Repeaters) in terms of their spectral and temporal variability. Here, we present our analysis of the current data set and show that (i) the energy spectrum is well modeled by a blackbody with two absorption lines, (ii) the spectral parameters do not show significant time variability over the last seven years, (iii) the pulse profile is strongly energy dependent, but stationary, and (iv) the pulse frequency evolution is consistent with monotonic spin-down. Our spectral and temporal results are consistent with earlier analyses by Schwope et al. [8] and Kaplan and van Kerkwijk [5], respectively. The inclusion of the new monitoring data provides more precise constraints on both spectral and temporal parameters of this INS. For isolated neutron stars whose X-ray emission is not powered by spin-down (INSs, AXPs and SGRs), RX J1308.6+2127 is among the most stable members. [ABSTRACT FROM AUTHOR]