RESUMO
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging X-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray-emitting region. The polarization degree is 4.01 ± 0.20% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. These observations reveal that hot x-ray-emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis.
RESUMO
Most active galactic nuclei (AGN) are 'obscured', i.e. the nucleus is hiding behind a screen of absorbing material. The advantage of having the nucleus obscured is to make easier the observations of those emission components which originate in circumnuclear matter outside the absorbing regions, because in this case they are not outshone by the nuclear emission. This is particularly important in X-rays, where spatial resolution is (with the notable exception of Chandra) poorer than in the optical, and the study of circumnuclear regions is often based on spectral analysis only. The properties of circumnuclear matter, in the light of recent high spectral and/or angular resolution Chandra and XMM-Newton observations, are reviewed and discussed in the framework of the unification model. Recent discoveries of X-ray obscured Seyfert 1, and of X-ray loud but optically normal galaxies, are calling for a revision of the unification model. Obscured AGN have also a cosmological relevance. Not only are they a fundamental ingredient of synthesis models of the cosmic X-ray background (XRB), but provide a link between the XRB and the cosmic infrared background.
