We report the first X-ray detection of the radio pulsar PSR B1757−24 using the Chandra X-ray Observatory. We detect point-source emission at the pulsar position plus a faint tail extending nearly 20 east of the pulsar, in the same direction and with comparable morphology to the radio tail. Assuming the point-source X-ray emission is magnetospheric, the observed X-ray tail represents only ∼0.01%...

The AGILE satellite detected several episodes of transient γ-ray emission from Cygnus X-3. Cross-correlating the AGILE light curve with both X-ray and radio monitoring data, we found that the main events of γ-ray activity were detected while the system was in soft spectral X-ray states, that coincide with local and often sharp minima of the hard X-ray flux, a few days before intense radio outbu...

The last years have seen a revolution in ground-based g-ray detectors. We can now detect the spectra of nearby TeV blazars like Mrk 421 and Mrk 501 out to ∼20 TeV, and during the strongest flares, we can now follow fluctuations in these spectra on timescales close to the shortest ones likely in these objects. We point out that this represents a unique opportunity. Using these and future detecto...

In 1998 we made UV spectroscopic observations with HST/STIS of A0620-00 and Cen X-4, which are two X-ray novae (aka soft X-ray transients). These binary systems are similar in all respects except that the former contains a black hole and the latter contains a neutron star. A UV spectrum (1700-3100Å) is presented for the quiescent state of each system in the context of previously published UV/op...

We present the results from simultaneous observations of the Narrow-Line Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating Spectrometer and the HST Space Telescope Imaging Spectrograph. The X-ray grating spectrum reveals absorption and emission lines from hydrogen-like and helium-like ions of O, Ne, Mg and Si. We resolve two distinct X-ray absorption systems: a high-ve...

Evolution of adiabatic remnants of an aspherical supernova explosion in uniform medium are considered. Thermal X-ray emission of such remnants are investigated. It is shown that integral thermal X-ray characteristics (X-ray luminosity and spectrum) of the objects do not allow us to reveal the assymetry in the explosion because these characteristics are close to their Sedov counterparts. Surface...

Quasars selected in optical surveys by means of their blue or UV excess are known to be strong emitters in the X-rays, except for Broad Absorption Line (BAL) objects. In this paper we study the X-ray emission of quasars selected through their emission line spectrum rather than their blue excess. X-ray data are obtained by cross-correlating two optical samples (the Hamburg Survey Catalogue and t...

PSR 1706−44 has been observed at energies above several hundred GeV in 2000 and 2001 using the CANGAROO-II 10m telescope. Above 1TeV, the spectrum is a steep power-law, which is consistent with previous results. However, the spectral index seems to change around 1TeV and becomes much flatter at lower energies. In addition, we analyzed Chandra X-Ray Observatory (Chandra) archival data to derive ...

our aim in this work is the synthesis and study optical and structural properties of gold nanoparticles.gold (iii) chloride trihydratewas taken as metal precursor, ascorbic acid at the presence of an appropriate amount of naoh as reducing agent and polyvinylpyrrolidonek-30 (pvp k-30) as a stabilizing and capping agent. the reaction was performed in high-speed stirring rate at room temperature.s...

We present a multiwavelength study of the black hole X-ray binary V404 Cyg in quiescence, focusing upon the spectral energy distribution (SED). Radio, optical, UV, and X-ray coverage is simultaneous. We supplement the SED with additional non-simultaneous data in the optical through infrared where necessary. The compiled SED is the most complete available for this, the X-ray and radio brightest ...