INTEGRAL observations of SS433: system's parameters and nutation of supercritical accretion disk

TL;DR

This study uses multiyear INTEGRAL and Swift/BAT data to analyze SS433's orbital and precessional X-ray variability, revealing disk nutation, a hot corona, and constraining the system's mass ratio, supporting a black hole presence.

Contribution

It provides the first detailed analysis of SS433's 18-60 keV orbital and precessional light curves, confirming disk nutation and constraining the binary mass ratio with new observational evidence.

Findings

Detection of nutation effects in the X-ray light curve.

Confirmation of a hot extended corona in SS433.

Constraints on the mass ratio indicating a black hole.

Abstract

Based on multiyear INTEGRAL observations of SS433 in 2003-2011, a composite IBIS/ISGRI 18-60 keV orbital light curve is constructed around zero precessional phases psi_{pr}= 0 at the maximim accretion disk opening angle. It shows a peculiar shape with significant excess near the orbital phase phi_orb= 0.25, which is not seen in the softer 2-10 keV energy band. The 40-60 keV orbital light curve demonstrates two almost equal humps at phases \sim 0.25 and \sim 0.75, most likely due to nutation effects of the accretion disk. The nutational variability of SS433 in 15-50 keV with a period of 6.290 days is independently found from timing analysis of Swift/BAT data. The change of the off-eclipse 18-60 keV X-ray flux with the precessional phase shows a double-wave form with strong primary maximum at psi_{pr}= 0 and weak but significant secondary maximum at psi_{pr}= 0.6. A weak variability of the 18-60 keV flux in the middle of the orbital eclipse correlated with the disk precessional phase is also observed. The joint analysis of the broadband 18-60 keV orbital and precessional light curves confirms the presence of a hot extended corona in the central parts of the supercritical accretion disk and constrains the binary mass ratio in SS433 in the range 0.5>q>0.3, suggesting the black hole nature of the compact object.