The disk/jet connection in the enigmatic microquasar Cygnus X-3

Abstract

Abstract. Simultaneous multi-wavelength observations are crucial for understanding the physics of microquasars, especially the accretion disk/jet connection. The enigmatic microquasar Cygnus X-3 exhibits strong, relativistic jet ejection events producing radio flares up to 20 Jy. These events are preceded by a very soft X-ray state with quenched emission in the radio and hard X-ray bands. Recently, GeV flux was observed by the AGILE and Fermi γ-ray observatories during the newly-identified hypersoft state. By using an extensive database of simultaneous multi-wavelength observations gathered from Cygnus X-3 we can form a more unified picture of the nature of the source and show how the recent γ-ray observations fit into it.

The remarkable timing properties of a ‘hypersoft’ state in GRO J1655-40

“…A similar spectral state has been noted and classified as the 'hypersoft state' by Koljonen et al (2010) in the high mass X-ray binary Cyg X-3. In Fig.…”

“…In its hypersoft state, Cyg X-3 shows bolometric luminosities of up to 4 × 10 38 erg s −1 (Koljonen et al 2010), several times larger than seen in GRO J1655-40. The system parameters of this Wolf-Rayet (WR) X-ray binary system are difficult to constrain and hence the nature of the compact object is unknown.…”

“…During the outburst the source showed a distinct type of soft state, lasting for ∼ 40 days and characterised by a very steep or absent power-law tail in its energy spectrum. We call this state the 'hypersoft' state, due to the strong similarity of its spectrum with that of the hypersoft state first classified in the HMXB Cyg X-3 by Koljonen et al (2010). A Chandra HETG observation obtained early in the hypersoft state of GRO J1655-40 showed evidence for a powerful equatorial disc wind, which seems to be specifically linked to this state and manifests itself in the RXTE PCA spectra as a strong edge from highly ionised iron.…”

“…Above 10 keV the two spectra are remarkably similar in shape as well as flux. Below 10 keV, the main differences may be due to the larger neutral absorbing column (few×10 22 cm −2 versus 7.4 × 10 21 cm −2 ) that is required to fit the spectrum in Cyg X-3 (Koljonen et al 2010). Considering the close similarity between the spectra above 10 keV, we will classify the unusual soft state of GRO J1655-40 as 'hypersoft' for the remainder of this paper.…”

The re-occurrence of mHz quasi-periodic oscillations in Cygnus X−3

“…The discrepancies between the reported results clearly show that these transient features are short-lived and sporadic or time-sensitive events. Interestingly, the previously discovered QPOs appear to occur following major radio flaring episodes (Koljonen et al 2011).…”