  Compact, steady jets are observed in the near infrared and radio bands in the
hard state of Galactic black hole transients as their luminosity decreases and
the source moves towards a quiescent state. Recent radio observations indicate
that the jets turn off completely in the soft state, therefore multiwavelength
monitoring of black hole transients are essential to probe the formation of
jets. In this work we conducted a systematic study of all black hole transients
with near infrared and radio coverage during their outburst decays. We
characterized the timescales of changes in X-ray spectral and temporal
properties and also in near infrared and/or in radio emission. We confirmed
that state transitions occur in black hole transients at a very similar
fraction of their respective Eddington luminosities. We also found that the
near infrared flux increase that could be due to the formation of a compact jet
is delayed by a time period of days with respect to the formation of a corona.
Finally, we found a threshold disk Eddington luminosity fraction for the
compact jets to form. We explain these results with a model such that the
increase in the near infrared flux corresponds to a transition from a patchy,
small scale height corona along with an optically thin out flow to a large
scale height corona that allows for collimation of a steady compact jet. We
discuss the timescale of jet formation in terms of transport of magnetic fields
from the outer parts of the disk, and also consider two alternative
explanations for the multiwavelength emission: hot inner accretion flows and
irradiation.
