X-ray Study on Propagation of Non-thermal Particles in Microquasar SS 433/W 50 Extended Jets

TL;DR

This study uses X-ray observations to analyze particle acceleration and spectral evolution in the eastern jets of SS 433, revealing differences from the western jets and suggesting additional physical processes like re-acceleration.

Contribution

It extends previous X-ray studies to the eastern jet of SS 433, providing new insights into spectral variations and physical processes involved in jet emission.

Findings

No detectable synchrotron emission between SS 433 and the eastern knot.

X-ray spectrum steepens with distance from SS 433 in the eastern jet.

Differences in spectral evolution between eastern and western jets imply additional physical processes.

Abstract

SS 433, located at the center of the W 50 radio nebula, is a binary system that ejects jets oriented east-west with precessional motion. X-ray lobes, containing compact "knots" labeled as head (e1), lenticular (e2), and ring (e3) in the east, as well as w1, w1.5, and w2 in the west, have been detected along the jets directions. Very-high-energy {\gamma}-ray emission has also been detected from regions containing these X-ray knots, suggesting highly efficient particle acceleration in the jets. In our previous study, we performed X-ray imaging spectroscopy of the western lobe of W 50 to investigate spectral variations. In this work, we extend our study to the eastern region using XMM-Newton observations to provide a more comprehensive picture of the X-ray emission from the SS 433 jets. Our results show no detectable synchrotron emission between SS 433 and the innermost knot (head). We also found that the X-ray spectrum of the eastern jet gradually steepens as one moves away from SS 433. While a similar spectral evolution is observed in the western jet, there are also noticeable differences. In the western lobe, the spectrum initially gradually steepens and then undergoes an abrupt softening outside the knot w2. However, in the eastern jet, no such rapid steepening is observed at the lenticular knot, which corresponds to w2 in the west. Furthermore, the observed brightening and spectral variations in the eastern jet cannot be explained by simply adjusting the parameters of the model used for the western side, suggesting the involvement of additional physical processes such as particle re-acceleration.