Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

Figure 15.1: A standard accretion disk (SAD) fed with ˙ Ma = 0.01LEdd/c 2 is established down to a radius rJ
which marks the transition towards a jet emitting disk (JED), settled down to the last stable orbit. The JED
is driving a mildly relativistic self-collimated electron-proton jet (MAES) which, when suitable conditions are
met, is confining and inner ultra-relativistic electron-positron beam. Field lines are drawn in red solid lines and
the number density is shown in greyscale (log 10 n/m −3 ).
However, observations require a rather large ejection to accretion ratio which can only be attained when there
is some heat deposition at the disk surface layers. This was again confirmed by near-IR modeling of the jet
emission (Pesenti et al. 2003). Finally, when taking into account observational biases in the detection of jet
rotation, disk-driven models with heat deposition are the best candidates (Pesenti et al. 2004, Ferreira et al.
2005, submitted). This work has been done in collaboration with members of the FOST team. Such heat
deposition has to come from local dissipation of the accretion energy, even in the presence of illumination by
stellar UV and X-ray fluxes (Garcia et al. 2005, submitted).
X-ray Binaries.
Microquasars are X-ray binaries where the primary is a black hole, displaying jets with an intriguing time
variability. Indeed, they change their spectral state from a ”High/Soft” (dominated by a soft disk component)
to a ”Low/Hard” (dominated by a hard power-law emission) state on time scales of hours. Jets are only seen
during the Low/Hard state. Moreover, it has been recently shown that this evolution is following an hysteresis
cycle. Therefore, these objects provide valuable clues on the secular evolution of the accretion-ejection process
(their dynamical time scale is the millisecond). Such transitions between spectral states would be unobservable
for AGNs.
Within our framework, a MAES is settled in the innermost disk regions surrounded by a standard accretion
disk as illustrated in Fig. 15.1 (Ferreira et al. 2005). This picture allows to explain several aspects of the
microquasar phenomenology: jet production in the Low/Hard state, jet quenching in the High/Soft state,
superluminal flares (pair plasma) under certain circumstances. Although each spectral state can be explained
by varying the relative importance of each component, several crucial questions remain to be investigated. This
requires a coupling between MHD and high energy physics and is therefore a central theme of our group.
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