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Register a new userEnergy estimation of high energy particles associated with the SS433/W50 system through radio observation at 1.4 GHz
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The radio nebula W50 is a unique object interacting with the jets of the microquasar SS433. The SS433/W50 system is a good target for investigating the energy of cosmic-ray particles accelerated by galactic jets. We report observations of radio nebula W50 conducted with the NSFs Karl G. Jansky Very Large Array (VLA) in the L band (1.0 -- 2.0 GHz). We investigate the secular change of W50 on the basis of the observations in 1984, 1996, and 2017, and find that most of its structures were stable for 33 years. 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 the observational data of the Arecibo Observatory 305-m telescope and identify the HI cavity around W50 in the velocity range 33.77 km s$^{-1}$ -- 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 10$^{15.5}$ 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 $times$ 10$^{48}$ erg.
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A new class of low-power compact radio sources with limited jet structures, named FR0, is emerging from recent radio-optical surveys. This abundant population of radio galaxies, five times more numerous than FRIs in the local Universe (z$<$0.05), represent a potentially interesting target at high and very-high energies (greater than 100 GeV), as demonstrated by a single case of Fermi detection. Furthermore, these radio galaxies have been recently claimed to contribute non-negligibly to the extra-galactic $gamma$-ray background and to be possible cosmic neutrino emitters. Here, we review the radio through X-ray properties of FR0s to predict their high-energy emission (from MeV to TeV), in light of the near-future facilities operating in this band.
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The microquasar SS433 features the most energetic jets known in our Galaxy. A large fraction of the jet kinetic power is delivered to the surrounding W50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. Here we report on the detection of a persistent gamma-ray signal from the direction of SS433/W50 with the Fermi Large Area Telescope. The steady flux and a narrow spectral energy distribution with a maximum around 250 MeV suggest that gamma-rays are rendered by the bulk jet kinetic power through proton-proton collisions at the SS433/W50 interaction regions. If the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution may represent a significant fraction of the total galactic cosmic-ray flux at GeV energies.
The W50/SS433 system is an unusual Galactic outflow-driven object of debatable origin. We have used the Australia Telescope Compact Array (ATCA) to observe a new 198 pointing mosaic, covering $3^circ times 2^circ$, and present the highest-sensitivity full-Stokes data of W50 to date using wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We also present a complementary H$alpha$ mosaic created using the Isaac Newton Telescope Photometric H$alpha$ Survey of the Northern Galactic Plane (IPHAS). The magnetic structure of W50 is found to be consistent with the prevailing hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR), that has been re-energised by the jets from SS433. We observe strong depolarization effects that correlate with diffuse H$alpha$ emission, likely due to spatially-varying Faraday rotation measure (RM) fluctuations of $ge48$ to 61 rad m$^{-2}$ on scales $le4.5$ to 6 pc. We also report the discovery of numerous, faint, H$alpha$ filaments that are unambiguously associated with the central region of W50. These thin filaments are suggestive of a SNRs shock emission, and almost all have a radio counterpart. Furthermore, an RM-gradient is detected across the central region of W50, which we interpret as a loop magnetic field with a symmetry axis offset by $approx90^{circ}$ to the east-west jet-alignment axis, and implying that the evolutionary processes of both the jets and the SNR must be coupled. A separate RM-gradient is associated with the termination shock in the Eastern ear, which we interpret as a ring-like field located where the shock of the jet interacts with the circumstellar medium. Future optical observations will be able to use the new H$alpha$ filaments to probe the kinematics of the shell of W50, potentially allowing for a definitive experiment on W50s formation history.
Galactic sites of acceleration of cosmic rays to energies of order 10^15 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In November 2020, the IceCube neutrino observatory reported an ~150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1-sigma (post trial) excess of atmospheric air showers from the same direction, observed by the Carpet-2 experiment and consistent with a few-months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma rays in a Galactic source.
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