High–resolution hydrodynamics simulations of the Lyα forest in cold dark matter dominated cosmologies appear to predict line widths that are substantially narrower than those observed. Here we point out that Compton heating of the intergalactic gas by the hard X–ray background (XRB), an effect neglected in all previous investigations, may help to resolve this discrepancy. The rate of gain in th...

High–resolution hydrodynamics simulations of the Lyα forest in cold dark matter dominated cosmologies appear to predict line–widths that are substantially narrower than those observed. Here we point out that Compton heating of the intergalactic gas by the hard X–ray background (XRB), an effect neglected in all previous investigations, may help to resolve this discrepancy. The rate of gain in th...

Context. The inverse Compton catastrophe is the dramatic rise in the luminosity of inverse-Compton scattered photons predicted to occur when the synchrotron brightness temperature exceeds a threshold value, usually estimated to be 1012 K. However, this effect appears to be in contradiction with observation because: (i) the threshold is substantially exceeded by several intra-day variable radio ...

High-resolution hydrodynamics simulations of the Lyα forest in cold dark matter dominated cosmologies appear to predict line widths that are substantially narrower than those observed. Here we point out that Compton heating of the intergalactic gas by the hard X–ray background (XRB), an effect neglected in all previous investigations, may resolve this discrepancy. The rate of gain in thermal en...

We use deep archival Chandra and XMM-Newton observations of three of the brightest cluster-centre radio galaxies in the sky, Cygnus A, Hercules A and Hydra A, to search for inverse-Compton emission from the population of electrons responsible for the low-frequency radio emission. Using simulated observations, we derive robust estimates for the uncertainties on the normalization of an inverse-Co...

PSR B1259−63 is a 47ms radio pulsar with a high spin-down luminosity which is in a close, highly eccentric 3.5-year orbit about a bright stellar companion. The binary system may be a detectable source of hard γ-rays produced by inverse Compton scattering of photons from the B2e star SS2883 by electrons and positrons in the pulsar wind. The star provides an enormous density of optical photons in...

Spectral analysis of ROSAT PSPC and ASCA archive data and a recent ROSAT HRI observation of the powerful FRII radio galaxy 3C 219 reveal an absorbed point–like source, coincident with the nucleus, and a non–thermal extended component aligned with the radio structure. The point– like source can be readily interpreted as a hidden quasar in the nucleus, giving further support to the unification sc...

Context. The inverse Compton catastrophe is the dramatic rise in the luminosity of inverse-Compton scattered photons predicted to occur when the synchrotron brightness temperature exceeds a threshold value, usually estimated to be 10 12 K. However, this effect appears to be in contradiction with observation because: (i) the threshold is substantially exceeded by several intra-day variable radio...

Using information on the cosmic X-ray background and the cumulative light of active galactic nuclei (AGN) at infrared wavelengths, published AGN composite spectra in the optical, UV and X-ray, and the estimated local mass density of galactic massive black holes (MBHs), we compute the characteristic angular-integrated, broad-band spectrum of the average quasar in the universe. We demonstrate tha...

The supranova model of gamma-ray bursts (GRBs), in which the GRB event is preceded by a supernova (SN) explosion by a few months to years, has recently gained support from Fe line detections in the Xray afterglows of some GRBs. A crucial ingredient of this model yet to be studied is the fast-rotating pulsar that should be active during the time interval between the SN and the GRB, driving a pow...