We investigate the γ-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) 4C 50.11 at redshift z = 1.517. The Fermi Large Area Telescope (LAT) data indicate that this source was in an active state since 2013 July. During the active period, the γ-ray flux increased by more than a factor of three and two distinct flares were detected with the variability timescale as short as several...

The preliminary detection of the Galactic Center black hole Sgr A* in X-rays by the Chandra mission, as well as recent mm-VLBI measurements, impose strict constraints on this source. Using a relativistic jet model for Sgr A*, we calculate the synchrotron and synchrotron self-Compton emission. The predicted spectrum provides an excellent fit to the radio spectrum and the X-ray observations. Limi...

We present X-ray observations of the interacting pair of galaxies NGC 4410a/b with the ROSAT HRI and PSPC. The ROSAT HRI images reveal a point-like source corresponding to NGC 4410a and an X-ray halo, extending 10 from the nucleus toward the southeast. The halo emission accounts for ∼1/3 (LX = 1.3×10 erg s in the 0.1 2.4 keV ROSAT band) of the total X-ray emission detected from NGC 4410a. The s...

We have spatially and spectrally resolved the sources of X-ray emission from the X-ray faint S0 galaxy NGC 1553 using an observation from the Chandra X-ray Observatory. The majority (70%) of the emission in the 0.3−10.0 keV band is diffuse, and the remaining 30% is resolved into 49 discrete sources. Most of the discrete sources associated with the galaxy appear to be low mass X-ray binaries (LM...

The Perseus galaxy cluster was observed by the MAGIC Cherenkov telescope for a total effective time of 24.4 hours during November and December 2008. No significant γ-ray excess was detected. The resulting upper limits on the γ-ray emission above 100 GeV are 4.63 and 6.55 × 10−12cm−2 s−1 for spectral indices of −1.5 and −2.2, respectively. The obtained limits constrain the emission produced by c...

Sub-arcsecond resolution Chandra observations of η Car reveal a 40 × 70 ring or partial shell of X-ray emission surrounding an unresolved, bright, central source. The spectrum of the central source is strongly absorbed and can be fit with a high-temperature thermal continuum and emission lines. The surrounding shell is well outside the optical/IR bipolar nebula and is coincident with the Outer ...

GRB 990123 was the Ðrst burst from which simultaneous optical, X-ray, and gamma-ray emission was detected ; its afterglow has been followed by an extensive set of radio, optical, and X-ray observations. We have studied the gamma-ray burst itself as observed by the Compton Gamma Ray Observatory detectors. We Ðnd that gamma-ray Ñuxes are not correlated with the simultaneous optical observations a...

We report here X-ray imaging spectroscopy observations of the northeastern shell of the supernova remnant RCW 86 with Chandra and XMM-Newton. Along this part of the shell the dominant X-ray radiation mechanism changes from thermal to synchrotron emission. We argue that both the presence of X-ray synchrotron radiation and the width of the synchrotron emitting region suggest a locally higher shoc...

We present a high-quality X-ray spectrum in the 3–53 keV rest-frame band of the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z > 4. A simple power-law model with an absorption column density equal to the Galactic value in the direction of the source provides an excellent and fully adequate fit to the data; the measured power-law photon index Γ = 1.42 −0.10. Upper limi...

It is believed that the observed diffuse gamma ray emission from the galactic plane is the result of interactions between cosmic rays and the interstellar gas. Such emission can be amplified if cosmic rays penetrate into dense molecular clouds. The propagation of cosmic rays inside a molecular cloud has been studied assuming an arbitrary energy and space dependent diffusion coefficient. If the ...