Observations of the C iv and Mg ii absorption lines in the Seyfert 1 galaxy NGC 4151 obtained with the GHRS in October 1994 are presented. The data from the STScI archive show multiple broad and narrow components in both species. In addition to Galactic absorption, four narrow and four broad systems associated with NGC 4151 are identified. Two broad systems dominate the total equivalent width, ...

We present the results of a two-year long optical monitoring program of the narrow-line Seyfert 1 galaxy Akn 564. The majority of this monitoring project was also covered by X-ray observations (RXTE) and for a period of ∼ 50 days, we observed the galaxy in UV (HST) and X-rays (RXTE & ASCA) simultaneously with the groundbased observations. Rapid and large-amplitude variations seen in the X-ray b...

We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray weak, far-infrared loud AGN, PG 1126−041 (Mrk 1298). The first UV spectra taken in June 1992, simultaneously with ROSAT, show strong absorption lines of NV, CIV and SiIV, extending over a velocity range from −1000 to −5000 km s with respect to the corresponding line centr...

We discuss the possible simultaneously UV/optical emission accompanying Gammaray bursts (GRBs). We show that as long as the intrinsic spectrum of GRB can extend to ∼10 GeV or higher, there is a large amount of relativistic e pairs generated due to the annihilation of the soft γ−rays with the very energetic photons, which dominates over the electrons/positrons associated with the fireball, no ma...

We use the observed optical-UV and X-ray emission spectrum of Cen X-4 during quiescence to constrain models for the accretion flow in this system. We argue that the optical-UV emission is not due to an optically-thick quiescent accretion disk, nor due to synchrotron emission from an Advection-Dominated Accretion Flow (ADAF). Emission from the bright spot could account for the observed optical-U...

in this paper, undopedzno and co-znonano structureswith different molar ratio of cobalt have been synthesized by the sonochemical method. structure have been characterized by fourier transform (ftir) and uv–vis spectroscopy,scanning electron microscopy (sem), energy dispersive analytical x-ray (edax), and x-ray diffraction (xrd) methods. moreover, the direct band gap has been calculated by tauc...

in this research zinc oxide (zno) nano-crystalline powders were prepared by sol-gel method using zinc acetate. the zno nanoparticles were characterized by x-ray diffraction (xrd), scanning electron microscopy (sem), ultraviolet-visible (uv-vis), fourier transform infra-red (ft-ir) and energy dispersive x-ray (edx) spectroscopy. the structure of nanoparticles was studied using xrd pattern. the c...

We consider the influence of microlensing on different spectral bands of lensed QSOs. We assumed that the emitting X-ray, UV and optical regions are different in size, but that the continuum emission in these spectral bands is originating from an accretion disc. Estimations of the time scales for microlensing and flux amplification in different bands are given. We found that the microlensing du...