1 research outputs found
A classification of the X-ray and radio states of Cyg X-3 and their long-term correlations
We present a detailed classification of the X-ray states of Cyg X-3 based on
the spectral shape and a new classification of the radio states based on the
long-term correlated behaviour of the radio and soft X-ray light curves. We
find a sequence of correlations, starting with a positive correlation between
the radio and soft X-ray fluxes in the hard spectral state, changing to a
negative one at the transition to soft spectral states. The temporal evolution
can be in either direction on that sequence, unless the source goes into a very
weak radio state, from which it can return only following a major radio flare.
The flare decline is via relatively bright radio states, which results in a
hysteresis loop on the flux-flux diagram. We also study the hard X-ray light
curve, and find its overall anticorrelation with the soft X-rays. During major
radio flares, the radio flux responds exponentially to the level of a hard
X-ray high-energy tail. We also specify the detailed correspondence between the
radio states and the X-ray spectral states. We compare our results to those of
black-hole and neutron-star binaries. Except for the effect of strong
absorption and the energy of the high-energy break in the hard state, the X-ray
spectral states of Cyg X-3 closely correspond to the canonical X-ray states of
black-hole binaries. Also, the radio/X-ray correlation closely corresponds to
that found in black-hole binaries, but it significantly differs from that in
neutron-star binaries. Overall, our results strongly support the presence of a
black hole in Cyg X-3.Comment: MNRAS, in pres