Hard X-ray emission from the eastern jet of SS 433 powering the W50 `Manatee' nebula: Evidence for particle re-acceleration

Samar Safi-Harb, Brydyn Mac Intyre, Shuo Zhang, Isaac Pope, Shuhan Zhang, Nathan Saffold, Kaya Mori, Eric V. Gotthelf, Felix Aharonian, Matthew Band, Chelsea Braun, Ke Fang, Charles Hailey, Melania Nynka, Chang D. Rho

Submitted on 1 July 2022


We present a broadband X-ray study of W50 (`the Manatee nebula'), the complex region powered by the microquasar SS 433, that provides a test-bed for several important astrophysical processes. The W50 nebula, a Galactic PeVatron candidate, is classified as a supernova remnant but has an unusual double-lobed morphology likely associated with the jets from SS 433. Using NuSTAR, XMM-Newton, and Chandra observations of the inner eastern lobe of W50, we have detected hard non-thermal X-ray emission up to 30 keV, originating from a few-arcminute size knotty region (`Head') located 18 (29 pc for a distance of 5.5 kpc) east of SS 433, and constrain its photon index to 1.58±0.05 (0.5-30 keV band). The index gradually steepens eastward out to the radio `ear' where thermal soft X-ray emission with a temperature kT0.2 keV dominates. The hard X-ray knots mark the location of acceleration sites within the jet and require an equipartition magnetic field of the order of 12μG. The unusually hard spectral index from the `Head' region challenges classical particle acceleration processes and points to particle injection and re-acceleration in the sub-relativistic SS 433 jet, as seen in blazars and pulsar wind nebulae.


Comment: 19 pages, 9 figures, 2 tables, accepted for publication in the Astrophysical Journal

Subject: Astrophysics - High Energy Astrophysical Phenomena