We present here high resolution X-ray spectrum of the accreting binary X-ray pulsar GX 1+4 obtained with the High Energy Transmission Grating (HETG) instrument of the Chandra X-ray Observatory. This was supplemented by a simultaneous observation with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE). During this observation, the source was in a somewhat low intensit...

A two-dimensional electrodynamic model is used to study particle acceleration and non-thermal emission mechanisms in the pulsar magnetospheres. We solve distribution of the accelerating electric field with the emission process and the pair-creation process in meridional plane, which includes the rotational axis and the magnetic axis. By solving the evolutions of the Lorentz factor, and of the p...

Dark matter annihilation in Galactic substructure produces diffuse gamma-ray emission of remarkably constant intensity across the sky, and in general this signal dominates over the smooth halo signal at angles greater than a few tens of degrees from the Galactic Center. The large-scale isotropy of the emission from substructure suggests that it may be difficult to extract this Galactic dark mat...

With the ASCA X-ray satellite, we perform spatial and spectral studies of the shell-type supernova remnant (SNR) γ Cygni that is associated with the brightest EGRET unidentified source 3EG J2020+4017. At energies below 3 keV the bulk of the X-ray flux from the remnant is well described by the emission of thermal plasma with characteristic temperature kTe ≃ 0.5–0.9 keV. In addition to this therm...

We report on BeppoSAX simultaneous Xand γ-ray observations of the bright γ-ray burst (GRB) 990123. We present the broad-band spectrum of the prompt emission, including optical, Xand γ-rays, confirming the suggestion that the emission mechanisms at low and high frequencies must have different physical origins. In the framework of the standard fireball model, we discuss the X-ray afterglow observ...

We present photoionization models accounting for both photoelectric and resonant absorption. We demonstrate that resonance absorption lines are detectable even in moderate resolution X-ray spectra of type 1 AGN. The spectra transmitted by gas illuminated by the ionizing continua typical of flat X-ray spectrum, broad optical emission line type 1 AGN, and steep X-ray spectrum, narrow optical emis...

We present spatially resolved Chandra HETGS observations of the Seyfert 2 galaxy NGC 1068. Xray imaging and high resolution spectroscopy are used to test the Seyfert unification theory. Fe Kα emission is concentrated in the nuclear region, as are neutral and ionized continuum reflection. This is consistent with reprocessing of emission from a luminous, hidden X-ray source by the obscuring molec...

We report on an XMM-Newton observation of the X-ray afterglow of the Gamma Ray Burst GRB 011211, originally detected by Beppo-SAX on 11th December 2001. The early afterglow spectrum obtained by XMM-Newton, observed 11 hours after the initial burst, appeared to reveal decaying H-like Kα emission lines of Mg, Si, S, Ar and Ca, arising in enriched material with an outflow velocity of order 0.1c (R...

Two sources of X-ray emission are expected from planetary nebulae: the hot central stars with Teff > 10 5 K, and shocked fast stellar winds at temperatures of 10 − 10 K. The stellar emission and nebular emission differ in spatial distribution and spectral properties. Observations of Xray emission from PNe may provide essential information on formation mechanisms and physical conditions of PNe. ...