Energy estimation of high-energy particles associated with the SS 433/W 50 system through radio observation at 1.4 GHz

Abstract

The radio nebula W 50 is a unique object interacting with the jets of the microquasar SS 433. The SS 433/W 50 system is a good target for investigating the energy of cosmic-ray particles accelerated by galactic jets. We report observations of the radio nebula W 50 conducted with the National Science Foundation’s Karl G. Jansky Very Large Array in the L band (1.0–2.0 GHz). We investigate the secular change of W 50 on the basis of the observations in 1984, 1996, and 2017, and find that most of its structures were stable for 33 yr. We revise the upper-limit velocity of the eastern terminal filament by half to 0.023 c, assuming a distance of 5.5 kpc. We also analyze observational data from the Arecibo Observatory 305 m telescope and identify the H i cavity around W 50 in the velocity range 33.77–55.85 km s−1. From this result, we estimate the maximum energy of the cosmic-ray protons accelerated by the jet terminal region to be above 1015.5 eV. We also use the luminosity of the gamma-rays in the range 0.5–10 GeV to estimate the total energy of accelerated protons below 5.2 × 1048 erg.

Molecular clouds at the eastern edge of radio nebula W50

“…The color is the integrated intensity of 12 CO(J=1-0) in the velocity range 30.1-42.3 km s −1 . These velocities correspond well to those of HI gas, suggesting a relation with W50 (Dubner et al 1998;Sakemi et al 2021). We refer to the newly identified prominent clouds as the chimney cloud and edge 0), the integrated intensity map of 13 CO(J=1-0) shows structures that are more clumpy.…”

“…A distance to the SS 433/W50 system of 3.0 kpc was determined from these results. Sakemi et al (2021) compared the spatial distributions of W50 and the surrounding HI using GALFA-HI survey datasets taken with the 305-m Arecibo Radio Telescope (Peek et al 2011) and confirmed that the HI cavity identified by Dubner et al (1998) has a clear spatial correlation with W50 in the velocity range from 33 to 55 km s −1 . Meanwhile, Lockman et al (2007) observed the absorption line of HI in the direction of SS 433 and concluded that the HI cloud at a velocity of 75 km s −1 is related to the SS 433/W50 system.…”

The high energy X-ray probe (HEX-P): Galactic PeVatrons, star clusters, superbubbles, microquasar jets, and gamma-ray binaries

“…In the western lobe, using the archival Chandra data (Moldowan et al, 2005;Kayama et al, 2022) recently extracted a detailed profile of spectral parameters along the western lobe (w1-w2), revealing that non-thermal X-ray emission begins at w1 (where the particle acceleration is initiated and most energetic) and becomes gradually softer toward w2 due to synchrotron cooling. In the radio band, an extensive VLA survey in the 1.4 GHz band was conducted over the entire W50 system, mapping synchrotron radiation emitted by lower-energy (GeV) electrons (Sakemi et al, 2021). As shown in Figure 8), the W50 "mini-AGN" system manifests all elements of astrophysical jets: acceleration sites (the inner lobes); particle propagation/cooling along the jet; and thermalization at the termination region.…”

“…Instead, broad-band X-ray spectroscopy and morphology studies with HEX-P, along with CTAO, will be critical in elucidating the origin of the TeV emission and constraining key model parameters such as magnetic field (B) and electron/proton spectral indices. The morphology data obtained by HEX-P, capturing non-thermal X-rays, will enable us to spatially correlate synchrotron X-ray emission with molecular clouds (Yamamoto et al, 2022) and radio features (Sakemi et al, 2021). Note that the molecular cloud and radio maps track the target material distribution for hadronic interactions and the magnetic field distribution, respectively.…”

Acceleration and transport of relativistic electrons in the jets of the microquasar SS 433

“…The morphology of W 50 indicates that the opening angle of the outer jets is considerably smaller than the 20° precession angle of the inner jets ( 19 ); the origin of this discrepancy is unknown ( 20 ). The lack of apparent change in the measured positions of radio filaments in the jet termination regions over a 33-year period provides an upper limit on their velocity of <0.023 c ( 21 , 22 ), although it is unclear whether the radio filaments trace the jets’ flow. Bright x-ray knots emitting synchrotron radiation have been observed in the outer jets, but the temporal baseline and angular resolution were insufficient to determine their velocity ( 23 ).…”