A NuSTAR view of SS433

Precessional evolution of the jet–disk system

¹ Instituto Argentino de Radioastronomía (CONICET; CICPBA), C.C. No 5, 1894 Villa Elisa, Argentina
e-mail: fafogantini@iar.unlp.edu.ar
² Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, B1900FWA La Plata, Argentina
³ Departamento de Ingeniería Mecánica y Minera (EPSJ), Universidad de Jaén, Campus Las Lagunillas s/n Ed. A3, 23071 Jaén, Spain
⁴ Université Paris Cité, CNRS, AstroParticule et Cosmologie, 75013 Paris, France
⁵ Departamento de Física (EPSJ), Universidad de Jaén, Campus Las Lagunillas s/n, A3, 23071 Jaén, Spain

Received: 2 May 2022
Accepted: 13 October 2022

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 T_o 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 T_o. 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 ∼ N_H/n_e0 ∼ 1.5 × 10⁹ cm ∼ 1700 r_g for M_BH = 3 M_⊙.