Relativistic Scattering in the Funnel of Cygnus X-3

Abstract

Cygnus X-3 presents significant challenges to standard accretion models. Recent polarimetric observations by IXPE reveal high polarization degrees (PD) in the hard state ($\sim 23\%$) and unexpectedly significant polarization in the soft state ($\sim 12\%$), which are difficult to reconcile with static scattering models at low inclination ($i\approx 30^{\circ }$). We present a relativistic scattering model within a funnel-shaped geometry that resolves this discrepancy. We show that a single funnel-outflow configuration with variable bulk velocity $\beta$ can reproduce both polarization states, with lower velocities ($\beta \approx 0$) yielding $\sim 12\%$ polarization (soft state) and mildly relativistic velocities ($\beta \lesssim 0.4$) producing $\sim 23\%$ polarization (hard state) at $i\approx 30^{\circ }$ for half funnel opening angles of $\sim 13^{\circ }$-$16^{\circ }$. Relativistic aberration modifies the effective scattering angle in the comoving frame, enhancing polarization in the hard state while recovering the static limit in the soft state. The model also yields a consistent estimate of the intrinsic luminosity, of order $\sim 10^{40}$ erg s${}^{-1}$, supporting a super-Eddington interpretation. This framework provides a unified explanation of the observed polarization properties of Cygnus X-3.

Accepted for publication in The Astrophysical Journal

References in corpus (6)

• Polarized X-rays from windy accretion in Cygnus X-1
• Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE
• A classification of the X-ray and radio states of Cyg X-3 and their long-term correlations
• Near-IR and X-ray Variability of Cyg X-3: Evidence for a Compact IR Source and Complex Wind Structures
• Ultrasoft state of microquasar Cygnus X-3: X-ray polarimetry reveals the geometry of astronomical puzzle
• Spectral Analysis of Cyg X-3 using simultaneous AstroSat and Insight-HXMT Observations