Energetics of a black hole: constraints on the jet velocity and the nature of the X-ray emitting region in Cyg X-1

We investigate the energetics of the jet and X-ray corona of Cyg X-1. We show that the current estimates of the jet power obtained from Halpha and [O III] measurements of the optical nebula surrounding the X-ray source allow one to constrain the bulk velocity of the jet. It is definitely relativistic (v >0.1c) and most probably in the range (0.3-0.8)c. The exact value of the velocity depends on the accretion efficiency. These constraints are obtained independently of, and are consistent with, previous estimates of the jet bulk velocity based on radio measurements. We then show that the X-ray emission does not originate in the jet. Indeed, the energy budget does not allow the corona to be ejected to infinity at relativistic speed. Rather, either a small fraction of the corona escapes to infinity, or the ejection velocity of the corona is vanishingly low. Although the corona could constitute the jet launching region, it cannot be identified with the jet itself. We discuss the consequences for various X-ray emission models.Comment: 9 pages, 4 figures, to appear in MNRA

Does the X-ray emission of the luminous quasar RBS 1124 originate in a mildly relativistic outflowing corona?

We have observed the luminous (L_x ~ 6x10^44 erg/s) radio-quiet quasar RBS 1124 (z=0.208) with Suzaku. We report the detection of a moderately broad iron (Fe) line and of a weak soft X-ray excess. The X-ray data are very well described by a simple model comprising a power law X-ray continuum plus its reflection off the accretion disc. If the inner disc radius we measure (<=3.8 gravitational radii) is identified with the innermost stable circular orbit of the black hole spacetime, we infer that the black hole powering RBS 1124 is rotating rapidly with spin a>= 0.6. The soft excess contribution in the 0.5-2 keV band is ~15%, about half than that typically observed in unobscured Seyfert 1 galaxies and quasars, in line with the low disc reflection fraction we measure (R_disc ~0.4). The low reflection fraction cannot be driven by disc truncation which is at odds not only with the small inner disc radius we infer but, most importantly, with the radiatively efficient nature of the source (L_Bol / L_Edd ~1). A plausible explanation is that the X-ray corona is the base of a failed jet (RBS 1124 being radio-quiet) and actually outflowing at mildly relativistic speeds. Aberration reduces the irradiation of the disc, thus forcing a lower than standard reflection fraction, and halves the inferred source intrinsic luminosity, reducing the derived Eddington ratio from ~1to ~0.5. [abridged]Comment: MNRAS in pres

Optical emission from massive donors in ULX binary systems

We present evolutionary tracks of binary systems with high mass companion stars and stellar-through-intermediate mass BHs. Using Eggleton's stellar evolution code, we compute the luminosity produced by accretion from the donor during its entire evolution. We compute also the evolution of the optical spectrum of the binary system taking the disc contribution and irradiation effects into account. The calculations presented here can be used to constrain the properties of the donor stars in Ultraluminous X-ray Sources by comparing their position on the HR or color-magnitude diagrams with the evolutionary tracks of massive BH binaries. This approach may actually provide interesting clues also on the properties of the binary system itself, including the BH mass. We found that, on the basis of their position on the color-magnitude diagram, some of the candidate counterparts considered can be ruled out and more stringent constraints can be applied to the donor masses.Comment: 11 pages, 7 figures. Submitted to MNRA

Probing the behaviour of the X-ray binary Cygnus X-3 with very-long-baseline radio interferometry

In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cyg X-3, we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival VLBA data at 5 or 15 GHz and new e-EVN data at 5 GHz. We also present 5 GHz MERLIN observations of an outburst of Cyg X-3. In the X-ray regime we use quasi-simultaneous with radio, monitoring and pointed RXTE observations. We find that when the radio emission from both jet and core is globally considered, the behaviour of Cyg X-3 at milliarcsecond scales is consistent with that described at arcsecond scales. However, when the radio emission is disentangled in a core component and a jet component the situation changes. It becomes clear that in active states the radio emission from the jet is dominating that from the core. This shows that in these states the overall radio flux cannot be used as a direct tracer of the accretion state.Comment: Accepted for publication in MNRA