Context. LS I+61 303 is one of the most interesting high-mass X-ray binaries owing to its spatially resolved radio emission and its TeV emission, generally attributed to non-thermal particles in an accretion-powered relativistic jet or in the termination shock of the relativistic wind of a young pulsar. Also, the nature of the compact object is still debated. Only LS 5039 and PSR B1259−63 (whic...

We have carried out a new study of the diffuse Galactic γ-ray continuum radiation using a cosmic-ray propagation model which includes nucleons, antiprotons, electrons, positrons, and synchrotron radiation. We show that models based on locally measured electron and nucleon spectra and synchrotron constraints are consistent with γ-ray measurements in the 30 MeV – 500 MeV range, but outside this r...

An analysis of a 29 ksec Chandra ACIS-S observations of the young, Cas-siopeia Alike supernova remnant in the irregular galaxy NGC 4449 is presented. The observed 0.5 − 2.1 keV spectrum reveals the likely presence of several emission lines including O VIII at 0.65 and 0.77 keV, Ne X at 1.05 keV, Mg XI at 1.5 keV, and Si XIII at 1.85 keV. From the observed spectrum, we derive an N H = 1 × 10 21 ...

We reanalyse archival GINGA and ASCA X–ray data from SS Cyg in both quiescence and outburst, using multi–temperature plasma models for the continuum and line emission, together with their reflection from the X–ray illuminated white dwarf and accretion disk. Reflection is clearly detected in all the spectra, but its contribution is larger in the softer X–ray spectra seen in outburst than in quie...

We present a study of the compatibility of some current models of the diffuse Galactic continuum γrays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the “conventional mo...

Clusters of galaxies have not yet been detected at gamma-ray frequencies; however, the recently launched Fermi Gamma-ray Space Telescope, formerly known as GLAST, could provide the first detections in the near future. Clusters are expected to emit gamma rays as a result of (1) a population of high-energy cosmic rays fueled by accretion, merger shocks, active galactic nuclei and supernovae, and ...

We present results of our study of correlated radio and X-ray emission in two black hole candidates and Galactic microquasars GRS 1915+105 and Cyg X-1 in their steady long term hard states, along with Cyg X-3 (using data obtained from Rossi X-Ray Timing Explorer all-sky monitor [RXTE-ASM], Compton Gamma Ray Observatory Burst and Transient Source Experiment [CGRO-BATSE], and Green Bank Interefer...

Context. The Sun has recently been predicted to be an extended source of gamma-ray emission, produced by inverse-Compton (IC) scattering of cosmic-ray (CR) electrons on the solar radiation field. The emission was predicted to be extended and a confusing foreground for the diffuse extragalactic background even at large angular distances from the Sun. The solar disk is also expected to be a stead...

We present results on the Seyfert 2 galaxy NGC4388 in the Virgo cluster observed with ASCA during its performance verification (PV) phase. The 0.5–10 keV X-ray spectrum consists of multiple components; (1) a continuum component heavily absorbed by a column density NH ≈ 4×10 cm above 3 keV; (2) a strong 6.4 keV line (equivalent width EW ∼ 500 eV); (3) a weak flat continuum between 1 and 3 keV; a...

We present here the rst images of impulsive millimeter emission of a are. The are on 1994 August 18 was simultaneously observed at millimeter (86 GHz), microwave (1-18 GHz), and soft and hard X{ray wavelengths. Images of millimeter, soft and hard X{ray emission show the same compact (< 8 00) source. Both the impulsive and the gradual phases are studied in order to determine the emission mechani...