SS 433 is a unique Galactic microquasar that exhibits persistent supercritical accretion and relativistic baryonic jets.
Its X-ray spectrum shows Doppler-shifted emission lines from bipolar jets, as well as a neutral Fe Ka line likely originating from the accretion disk.
We observed SS 433 with XRISM in April 2024 over a five-day period, covering both eclipse and non-eclipse phases of the compact object by the companion star.
Using Resolve, the X-ray microcalorimeter that delivers unprecedented energy resolution (~5 eV at 6 keV) with high sensitivity, we obtained a high-quality X-ray spectrum of SS 433.
The Resolve spectrum clearly resolved Doppler-shifted, ionized Fe and Ni K emission lines, along with lower-energy features such as Si and S K lines.
Time-resolved spectroscopy revealed that the Fe and Ni K line widths were ~20 eV (corresponding to a 1-sigma velocity dispersion of ~1000 km/s) during eclipse, increasing gradually during egress, and reaching ~35 eV (~1800 km/s) outside the eclipse.
Furthermore, the time-averaged spectrum outside eclipse showed that Fe and Ni K lines are significantly broader than the Si and S lines, consistent with previous Chandra/HETGS results Namiki et al. (2003).
This suggests that the velocity dispersion of the jets decreases with distance from the compact object, likely due to progressive collimation or reduced turbulence in the outer regions.
We also analyzed the neutral Fe Ka line at ~6.4 keV.
Modeling it with a disk emission line model, we found that it is likely originating from the outermost part of the disk.
In this article, we report these results and discuss the spatial structure of the accretion disk and jets inferred from the observed emission lines.