Synergism between results from multiwavelength simultaneous observations in microquasars and quasars is providing important insights into the connection between accretion disk instabilities and the genesis of jets. Since the characteristic times in the flow of matter onto a black hole are proportional to its mass, the accretion-ejection phenomena in quasars should last 105-107 longer than analogous phenomena in microquasars (Sams et al. 1996). Therefore, variations on scales of tens of minutes of duration in microquasars could be sampling phenomena that had been difficult to observe in quasars.
Simultaneous
multiwavelength observations of a microquasar revealed in an interval of
time of a few tens of minutes the connection between the sudden
disappearance of the inner ~ 200 km of the accretion disk
with the ejection of expanding clouds of relativistic plasma (see
Figure 2).
One possible interpretation of the observations shown in
Figure 2 is that the plasma
of the inner disk that radiates in the X-rays falls beyond the horizon
of the black hole in ~ 5min, and subsequently the inner accretion disk is
refilled in ~ 20 min. While the inner disk is being replenished,
we observe the ejection of a relativistic plasma cloud, first
at 2µm, and latter at radio wavelengths as the cloud expands
and becomes transparent for its proper radiation at longer wavelengths.
The delay between the maxima at radio and
infrared wavelengths is equal to the one computed with the model for
a spherically symmetric expanding clouds in relativistic AGN jets by
van der Laan (1966).
Although VLBA images of these transient ejecta by
Dhawan et al. (2000)
have shown that they are in fact connical jets, the model
first developed for AGN is a good first approximation, and allows
to demonstrate
that the infared flares that preceed the radio flares are synchrotron,
rather than thermal emission. This implies the presence in the jets of
electrons with Lorentz factors
103
(Fender & Pooley,
1998;
Mirabel et al. 1998).
 |
Figure 2. Radio, infrared, and X-ray light curves for GRS 1915+105 at the time of quasi-periodic oscillations with scales of time of ~ 20 min (Mirabel et al. 1998). The infrared flare starts during the recovery from the X-ray dip, when a sharp, isolated X-ray spike-like feature is observed. These observations show the connection between the rapid disappearance and follow-up replenishment of the inner accretion disk seen in the X-rays (Belloni et al. 1997), with the ejection of relativistic plasma clouds observed first as synchrotron emission at infrared wavelengths, later at radio wavelengths. A scheme of the relative positions where the different emissions originate is shown in the top part of the figure. The hardness ratio (13-60 keV) / (2-13 keV) is shown at the bottom of the figure. Analogous phenomena have now been obseved in the quasar 3C 120 but in time scales of years (Marscher et al. 2002). |
Analogous accretion disk-jet connections were observed in the quasar 3C 120 by Marscher et al. (2002). Jets were detected with VLBI after sudden X-ray dips observed with RXTE, but on scales of a few years. The scales of time of the phenomena are within a factor of 10 the black hole mass ratios between the quasar and microquasar, which is relativelly small when compared with the uncertainties in the data.