A NuSTAR view of SS433

Abstract

Context. SS433 is a Galactic microquasar with powerful outflows (double jet, accretion disk and winds) with a well-known orbital, precessional, and nutational period. Aims. In this work we characterise different outflow parameters throughout the precessional cycle of the system. Methods. We analysed ten NuSTAR (3–70 keV) observations of ∼30 ks that span ∼1.5 precessional cycles. We extracted averaged spectra and modelled them using a combination of a double thermal jet model (bjet) and pure neutral and relativistic reflection (xillverCp and relxilllpCp) over an accretion disk. Results. We find an average jet bulk velocity of β = v/c ∼ 0.29 with an opening angle of ≲6 deg. Eastern jet kinetic power ranges from 1 to 1039 erg s−1, with base ‘coronal’ temperatures To ranging from between 14 and 18 keV. Nickel-to-iron abundances remain constant at ∼9 (within 1σ). The western to eastern jet-flux ratio becomes ∼1 on intermediate phases, which is about 35% of the total precessional orbit. The 3–70 keV total unabsorbed luminosity of the jet and disk ranges from 2 to 20 × 1037 erg s−1, with the disk reflection component mainly contributing to the hard 20–30 keV excess and the stationary 6.7 keV ionised Fe line complex. Conclusions. At low opening angles Θ, we find that the jet expands sideways following an adiabatic expansion of a gas with temperature To. Finally, the central source and lower parts of the jet could be hidden by an optically thick region of τ > 0.1 and size R ∼ NH/ne0 ∼ 1.5 × 109 cm ∼ 1700 rg for MBH = 3 M⊙.