We have discovered a Narrow-Line Seyfert 1 (NLS1) galaxy and identified it with an ultrasoft X-ray source (RX 215319-1514) detected with ROSAT . We present its X-ray and optical spectral characteristics. Its redshift is found to be 0.0778±0.0002. Its optical spectrum shows fairly strong Fe II emission lines, and its X-ray spectrum has an extremely steep power-law index of Γ ≥4, making it an ext...

We present new XM M − N ewton X-ray observations of the z = 1.246 narrow-line radioquasar RX J1011.2+5545 serendipitously discovered by ROSAT. The flat X-ray spectrum previously measured by ROSAT and ASCA is shown to be the result of a steep Γ ∼ 1.8 power law spectrum seen through a moderate intrinsic absorbing column (N H ∼ 4 × 10 21 cm −2). The position of the X-ray source is entirely coincid...

We perform Monte Carlo simulations of cosmic-ray induced hard X-ray emission in the Earth’s atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range ∼25–300 keV is determined by Compton scattering and photoabsorption and is virtually independent of the incident cosmic ray spectrum. We provide a fitting formula for the spectral intensity as a function o...

We present hard X-ray observations of the nearby radio galaxy M87 and the core of the Virgo cluster using the Rossi X-ray Timing Explorer. These are the first hard X-ray observations of M87 not affected by contamination from the nearby Seyfert 2 galaxy NGC 4388. Thermal emission from Virgo’s intracluster medium is clearly detected and has a spectrum indicative of kT ≈ 2.5 keV plasma with approx...

We present hard X-ray observations of the nearby radio galaxy M87 and the core of the Virgo cluster using the Rossi X-ray Timing Explorer. These are the first hard X-ray observations of M87 not affected by contamination from the nearby Seyfert 2 galaxy NGC 4388. Thermal emission from Virgo’s intracluster medium is clearly detected and has a spectrum that is well described by a kT ≈ 2.7 keV ther...

We examine the possibility that Ultraluminous X-ray sources (ULXs) represent the extreme end of the black hole X-ray binary (XRB) population. Based on their X-ray properties, we suggest that ULXs are persistently in a high/hard spectral state and we propose a new disk–jet model that can accomodate both a high accretion rate and a hard X-ray spectrum. Our model predicts that the modified disk em...

We present hard X-ray observations of the nearby radio galaxy M87 and the core of the Virgo cluster using the Rossi X-ray Timing Explorer. These are the first hard X-ray observations of M87 not affected by contamination from the nearby Seyfert 2 galaxy NGC 4388. Thermal emission from Virgo’s intracluster medium is clearly detected and has a spectrum that is well described by a kT 2:5 keV therma...

During a systematic search for periodic signals in a sample of ROSAT PSPC light curves, we discovered ∼ 8.9 s X–ray pulsations in 2E0050.1–7247, a variable X–ray source in the Small Magellanic Cloud. The source was detected several times between 1979 and 1993 at luminosity levels ranging from ∼ 5 × 10 erg s up to 1.4 × 10 erg s with both the Einstein IPC and ROSAT PSPC. The X–ray energy spectru...

Chandra observations of the type 1.8, low-redshift (z 1⁄4 0:115), red (J KS 2) quasar 2MASSJ 104943+583750 (2M1049+5837) indicated an unusually hardX-ray spectrum (HR 0:6), suggesting obscuration ofNH 4 ; 10 cm 2 and a flat 0:4 power-law slope. A higher signal-to-noise ratio XMM-Newton observation reported here reveals a more complex spectrum, being extremely hard above 2 keV, 0:6, with a well-...