We present a unified semi-quantitative model for the disc-jet coupling in black hole X-ray binary systems. We argue that during the rising phase of a black hole transient outburst the steady jet known to be associated with the canonical 'low/hard' state persists while the X-ray spectrum initially softens. Subsequently, the jet becomes unstable and an optically thin radio outburst is always associated with the soft X-ray peak at the end of this phase of softening. This peak corresponds to a 'soft very high state' or 'steep power law' state. Softer X-ray states are not associated with 'core' radio emission. We further demonstrate quantitatively that the transient jets associated with these optically thin events are considerably more relativistic than those in the 'low/hard' X-ray state. This in turn implies that as the disc makes its collapse inwards the jet Lorentz factor rapidly increases, resulting in an internal shock in the outflow, which is the cause of the observed optically thin radio emission. In addition, we estimate the jet power for a number of such transient events as a function of X-ray luminosity, and find them to be comparable to an extrapolation of the functions estimated for the 'low/hard' state jets. Finally, we attempt to fit these results together into a coherent semi-quantitative model for the disc-jet coupling in all black hole X-ray binary systems (abridged).Comment: Accepted for publication in MNRA

Several independent lines of evidence now point to a connection between the physical processes that govern radio (i.e. jet) and X‐ray emission from accreting X‐ray binaries. We present a comprehensive study of (quasi‐)simultaneous radio–X‐ray observations of stellar black hole binaries during the spectrally hard X‐ray state, finding evidence for a strong correlation between these two bands over more than three orders of magnitude in X‐ray luminosity. The correlation extends from the quiescent regime up to close to the soft state transition, where radio emission starts to decline, sometimes below detectable levels, probably corresponding to the physical disappearance of the jet. The X‐ray transient V404 Cygni is found to display the same functional relationship already reported for GX 339−4 between radio and X‐ray flux, namely Sradio∝S+0.7X. In fact, the data for all low/hard state black holes is consistent with a universal relation between the radio and X‐ray luminosity of the form Lradio∝L+0.7X. Under the hypothesis of common physics driving the disc–jet coupling in different sources, the observed spread to the best‐fitting relation can be interpreted in terms of a distribution in Doppler factors and hence used to constrain the bulk Lorentz factors of both the radio‐ and X‐ray‐emitting regions. Monte Carlo simulations show that, assuming little or no X‐ray beaming, the measured scatter in radio power is consistent with Lorentz factors ≲ 2 for the outflows in the low/hard state, significantly less relativistic than the jets associated with X‐ray transients. When combined radio and X‐ray beaming is considered, the range of possible jet bulk velocities significantly broadens, allowing highly relativistic outflows, but therefore implying severe X‐ray selection effects. If the radio luminosity scales as the total jet power raised to x > 0.7, then there exists an X‐ray luminosity below which most of the accretion power will be channelled into the jet, rather than into X‐rays. For x= 1.4, as in several optically thick jet models, the power output of ‘quiescent’ black holes may be jet‐dominated below LX≃ 4 × 10−5LEdd.

Accreting black holes are thought to emit the bulk of their power in the X-ray band by releasing the gravitational potential energy of the infalling matter 1 . At the same time, they are capable of producing highly collimated jets of energy and particles flowing out of the system with relativistic velocities 2 . Here we show that the 10 solar mass black hole in the Xray binary Cygnus X-1 3,4,5 is surrounded by a large-scale (about 5 pc in diameter) ring-like structure that appears to be inflated by the inner radio jet 6 . We estimate that in order to sustain the observed emission of the ring, the jet of Cygnus X-1 has to carry a kinetic power that can be as high as the bolometric X-ray luminosity of the binary system. This result may imply that low-luminosity stellar mass black holes as a whole dissipate the bulk of the liberated accretion power in the form of 'dark', radiatively inefficient relativistic outflows, rather than locally in the X-ray emitting inflow.

Loeys-Dietz syndrome (LDS) associates with a tissue signature for high transforming growth factor (TGF)-β signaling but is often caused by heterozygous mutations in genes encoding positive effectors of TGF-β signaling, including either subunit of the TGF-β receptor or SMAD3, thereby engendering controversy regarding the mechanism of disease. Here, we report heterozygous mutations or deletions in the gene encoding the TGF-β2 ligand for a phenotype within the LDS spectrum and show upregulation of TGF-β signaling in aortic tissue from affected individuals. Furthermore, haploinsufficient Tgfb2+/− mice have aortic root aneurysm and biochemical evidence of increased canonical and noncanonical TGF-b signaling. Mice that harbor both a mutant Marfan syndrome (MFS) allele (Fbn1C1039G/+) and Tgfb2 haploinsufficiency show increased TGF-β signaling and phenotypic worsening in association with normalization of TGF-β2 expression and high expression of TGF-β1. Taken together, these data support the hypothesis that compensatory autocrine and/or paracrine events contribute to the pathogenesis of TGF-β–mediated vasculopathies.

Deep observations with the Very Large Array of A0620–00, performed in 2005 August, resulted in the first detection of radio emission from a black hole binary at X‐ray luminosities as low as 10−8.5 times the Eddington limit. The measured radio flux density, of 51 ± 7 μJy at 8.5 GHz, is the lowest reported for an X‐ray binary system so far, and is interpreted in terms of partially self‐absorbed synchrotron emission from outflowing plasma. Making use of the estimated outer accretion rate of A0620−00 in quiescence, we demonstrate that the outflow kinetic power must be energetically comparable to the total accretion power associated with such rate, if it was to reach the black hole with the standard radiative efficiency of 10 per cent. This favours a model for quiescence in which a radiatively inefficient outflow accounts for a sizable fraction of the missing energy, and, in turn, substantially affects the overall dynamics of the accretion flow. Simultaneous observations in the X‐ray band, with Chandra, confirm the validity of a non‐linear radio/X‐ray correlation for hard state black hole binaries down to low quiescent luminosities, thereby contradicting some theoretical expectations. Taking the mass term into account, the A0620−00 data lie on the extrapolation of the so‐called Fundamental Plane of black hole activity, which has thus been extended by more than two orders of magnitude in radio and X‐ray luminosity. With the addition of the A0620−00 point, the plane relation provides an empirical proof for the scale invariance of the jet‐accretion coupling in accreting black holes over the entire parameter space observable with current instrumentation.

We demonstrate that at relatively low mass accretion rates, black hole candidate (BHC) X-ray binaries (XRBs) should enter 'jet-dominated' states, in which the majority of the liberated accretion power is in the form of a (radiatively inefficient) jet and not dissipated as X-rays in the accretion flow. This result follows from the empirically established non-linear relation between radio and X-ray power from low/hard state BHC XRBs, which we assume also to hold for neutron star (NS) XRBs. Conservative estimates of the jet power indicate that all BHC XRBs in 'quiescence' should be in this jet-dominated regime. In combination with an additional empirical result, namely that BHC XRBs are more 'radio-loud' than NS XRBs, we find that in quiescence NS XRBs should be up to two orders of magnitude more luminous in X-rays than BHC XRBs, without requiring any significant advection of energy into a black hole. This ratio is as observed, and such observations should therefore no longer be considered as direct evidence for the existence of black hole event horizons. Furthermore, even if BHCs do contain black holes with event horizons, this work demonstrates that there is no requirement for the advection of significant amounts of accretion energy across the horizon.

Development and repair of the vertebrate skeleton requires the precise coordination of bone-forming osteoblasts and bone-resorbing osteoclasts. In diseases such as osteoporosis, bone resorption dominates over bone formation, suggesting a failure to harmonize osteoclast and osteoblast function. Here, we show that mice expressing a constitutively nuclear NFATc1 variant (NFATc1(nuc)) in osteoblasts develop high bone mass. NFATc1(nuc) mice have massive osteoblast overgrowth, enhanced osteoblast proliferation, and coordinated changes in the expression of Wnt signaling components. In contrast, viable NFATc1-deficient mice have defects in skull bone formation in addition to impaired osteoclast development. NFATc1(nuc) mice have increased osteoclastogenesis despite normal levels of RANKL and OPG, indicating that an additional NFAT-regulated mechanism influences osteoclastogenesis in vivo. Calcineurin/NFATc signaling in osteoblasts controls the expression of chemoattractants that attract monocytic osteoclast precursors, thereby coupling bone formation and bone resorption. Our results indicate that NFATc1 regulates bone mass by functioning in both osteoblasts and osteoclasts.

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