A NuSTAR view of SS433: precessional evolution of the jet-disk system

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/c0.29 with an opening angle of ²6 deg. Eastern jet kinetic power ranges from 1 to 1039 erg s 1, with base temperatures To ranging from between 14 and 18 keV. Nickel-to-iron abundances remain constant at 9 (within 1I). 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 Ã - 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 Î , 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 I >0.1 and size RNH/ne01.5 Ã - 109cm1700rg for MBH=3M-.