I briefly outline the state-paradigm that has emerged from the study of black-hole binaries with RossiXTE. This is the starting point of a number of studies that address the connection between accretion and jet ejection and the physical nature of the hard spectral components in these systems.
Deep Dive into Spectral/timing evolution of black-hole binaries.
I briefly outline the state-paradigm that has emerged from the study of black-hole binaries with RossiXTE. This is the starting point of a number of studies that address the connection between accretion and jet ejection and the physical nature of the hard spectral components in these systems.
State transitions are sharp: although obviously the 3-20 keV energy spectrum cannot be much different when crossing the vertical lines, detailed analysis of the properties of fast aperiodic variability shows that indeed marked changes take place there (see Belloni 2009). Therefore, the position of the transition lines is not at all arbitrary, but is
In the past few years, thanks to an increased observational radio/X-ray activity, a picture of the connection between accretion and ejection is also emerging (see Fender 2009;Gallo 2009). In particular, it is now clear that while the LHS is associated to compact radio jets and the HSS to quenched radio emission, the major jet ejections take place during intermediate states. Fender, Belloni & Gallo (2004) identified the QPO-line with the position corresponding to the ejection of fast jets (the “Jet-line”). However, recently Fender, Homan & Belloni (2009) found that this association is not perfect nor causal: the two lines are crossed within a couple of weeks from each other, in either sequence.
Although across transitions the energy spectrum does not change appreciably, once energies above 20 keV are considered the picture changes. In particular, recent results on GX 339-4 have shown that the high-energy cutoff of the hard spectral component changes in non-monotonic way across the transition (Motta et al. 2009). Figure 2 shows the evolution of this parameter as a function of hardness, over the path sketched in black in Fig. 1. in the LHS, the high-energy cutoff decreases from 120 to 60 keV as the sources brightens (and softens), then the trend is reversed and in the HIMS there is a marked increase back to ∼100 keV. After the QPO-line, the cutoff energy is high, possibly not detected significantly (see also Motta et al., this volume). This evolution is rather complex. Although the LHS behaviour is simple to understand, as the simultaneous increased soft emission cools the electrons responsible for the Comptonization. However, the trend reversal is still puzzling.
We now have a clear phenomenological picture of the evolution of black-hole transients, which can be compared to that of neutron-star binaries and active galactic nuclei (see Belloni 2009). It is clear that state-transitions hold the key to a deeper understanding.
Although they are transient and difficult to observe, the data already existing show that the spectral evolution is complex and still needs to be understood.
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