The Square Kilometre Array (SKA)

Abstract:

Abstract We present soft X-ray spectroscopy of the black-hole X-ray binary V4641 Sgr with the XMM-Newton Reflection Grating Spectrometer (RGS). The RGS spectrum shows narrow emission features from N vi–vii and O vii–viii superimposed on a partially covered disk blackbody continuum. A blind Gaussian search confirms the presence of significant lines at the expected rest wavelengths. He-like triplet ratios (high G, low R) and full photoionization modelling both indicate a dense, photoionized plasma. Small redshifted velocities of ~540–720 km s−1 are suggested, which are consistent with quasi-static or slowly flowing gas away from the observer after accounting for systematics. Photoionization modelling requires two xstar components with an intermediate ionization parameter (log ξ ≃ 3.1) and a low ionization parameter (log ξ ≃ 0.36), respectively. The simultaneous EPIC-pn spectrum suggests highly ionized Fe emission structures, hinting at an additional, more highly ionized component. These results imply the existence of a radially extended, multiphase, and dense disk atmosphere in the source. We compare the source with other X-ray binaries showing similar emission lines. V4641 Sgr shares a similarly high inclination with other sources; however, the presence of low ionization emission lines distinguishes it from the rest.

Abstract:

Abstract We have recently shown evidence that the most relativistic jets (with Lorentz factor >2) from stellar-mass black holes in X-ray binary systems may be locked to a fixed axis, likely the spin axis of the black hole. Slower, mildly relativistic jets (with velocities typically ~0.3c) are often seen to precess and can be associated with both neutron stars and black holes. In this paper we demonstrate an additional clear link between highly obscured systems and these lower-velocity, precessing jets. We speculate that this link may be due to mass-loading of the jets close to their launch sites, since these obscured systems are likely to be examples of (sometimes persistent, other times transient) super-Eddington accretion. The fastest relativistic jets are now seen to be both locked to a fixed direction, likely the black hole spin axis, and to be launched in low-density environments, while jets launched in dense environments are generally slower and very likely to precess.