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 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...

Combining archival data taken at radio and infrared wavelengths with state-of-the-art measurements at X-ray and gamma-ray energies, we assembled a broadband spectral energy distribution (SED) of Cas A, a young supernova remnant. Except for strong thermal emission at infrared and X-ray wavelengths, the SED is dominated by nonthermal radiation. We attempted to model the non-thermal SED with a two...

Prompt optical emission from the γ-ray burst of GRB 041219A has been reported by Vestrand et al. There was a fast rise of optical emission simultaneous with the dominant γ-ray pulse, and a tight correlation with the prompt γ-ray emission has been displayed. These indicate that the prompt optical emission and γ-ray emission would naturally have a common origin. We propose that this optical compo...

The Galactic plane is a strong emitter of hard x-rays (2 to 10 kiloelectron volts), and the emission forms a narrow continuous ridge. The currently known hard x-ray sources are far too few to explain the ridge x-ray emission, and the fundamental question of whether the ridge emission is ultimately resolved into numerous dimmer discrete sources or truly diffuse emission has not yet been settled....

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...

The all-sky survey in high-energy gamma rays (E>30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation as well an ...

The evolution of X-ray emission from young massive star clusters is modeled, taking into account the emission from the stars as well as from the cluster wind. It is shown that the level and character of the soft (0.2-10 keV) X-ray emission change drastically with cluster age and are tightly linked with stellar evolution. Using the modern X-ray observations of massive stars we show that the corr...

The rapidly varying non-thermal X-ray emission observed from Sgr A⋆ points to particle acceleration taking place close to the supermassive black hole. The TeV γ-ray source HESS J1745−290 is coincident with Sgr A⋆ and may be closely related to the X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these two objects. Here we report on joint ...