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Register a new userGamma-ray heartbeat powered by the microquasar SS 433
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Microquasars, the local siblings of extragalactic quasars, are binary systems comprising a compact object and a companion star. By accreting matter from their companions, microquasars launch powerful winds and jets, influencing the interstellar environment around them. Steady gamma-ray emission is expected to rise from their central objects, or from interactions between their outflows and the surrounding medium. The latter prediction was recently confirmed with the detection of SS 433 at high (TeV) energies. In this report, we analyze more than ten years of GeV gamma-ray data from the Fermi Gamma-ray Space Telescope on this source. Detailed scrutiny of the data reveal emission in the SS 433 vicinity, co-spatial with a gas enhancement, and hints for emission possibly associated with a terminal lobe of one of the jets. Both gamma-ray excesses are relatively far from the central binary, and the former shows evidence for a periodic variation at the precessional period of SS 433, linking it with the microquasar. This result challenges obvious interpretations and is unexpected from any previously published theoretical models. It provides us with a chance to unveil the particle transport from SS 433 and to probe the structure of the local magnetic field in its vicinity.
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SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star). Two jets of ionized matter with a bulk velocity of $sim0.26c$ extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets. SS 433 differs from other microquasars in that the accretion is believed to be super-Eddington, and the luminosity of the system is $sim10^{40}$ erg s$^{-1}$. The lobes of W50 in which the jets terminate, about 40 pc from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed. At higher energies (>100 GeV), the particle fluxes of $gamma$ rays from X-ray hotspots around SS 433 have been reported as flux upper limits. In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons interacting with the ambient gas. Here we report TeV $gamma$-ray observations of the SS 433/W50 system where the lobes are spatially resolved. The TeV emission is localized to structures in the lobes, far from the center of the system where the jets are formed. We have measured photon energies of at least 25 TeV, and these are certainly not Doppler boosted, because of the viewing geometry. We conclude that the emission from radio to TeV energies is consistent with a single population of electrons with energies extending to at least hundreds of TeV in a magnetic field of $sim16$~micro-Gauss.
The detection of two sources of gamma rays towards the microquasar SS 433 has been recently reported. The first source can be associated with SS 433s eastern jet lobe, whereas the second source is variable and displays significant periodicity compatible with the precession period of the binary system, of about 160 days. The location of this variable component is not compatible with the location of SS 433 jets. To explain the observed phenomenology, a scenario based on the illumination of dense gas clouds by relativistic protons accelerated at the interface of the accretion disk envelope has been proposed. Energetic arguments strongly constrain this scenario, however, as it requires an unknown mechanism capable to periodically channel a large fraction of SS 433s kinetic energy towards an emitter located 36 parsec away from the central binary system.
We investigate hadronic and leptonic scenarios for the GeV--TeV gamma-ray emission from jets of the microquasar SS 433. The emission region of the TeV photons coincides with the X-ray knots, where electrons are efficiently accelerated. On the other hand, the optical high-density filaments are also located close to the X-ray knots, which may support a hadronic scenario. We calculate multi-wavelength photon spectra of the extended jet region by solving the transport equations for the electrons and protons. We find that both hadronic and leptonic models can account for the observational data, including the latest {it Fermi} LAT result. The hadronic scenarios predict higher-energy photons than the leptonic scenarios, and future observations such as with the Cherenkov Telescope Array (CTA), the Large High-Altitude Air Shower Observatory (LHAASO), and the Southern Wide-field Gamma-ray Observatory (SWGO) may distinguish between these scenarios and unravel the emission mechanism of GeV--TeV gamma-rays. Based on our hadronic scenario, the analogy between microquasars and radio galaxies implies that the X-ray knot region of the radio-galaxy jets may accelerate heavy nuclei up to ultrahigh energies.
We present a study of the mass transfer and wind outflows of SS433, focusing on the so-called stationary lines based on archival high and low resolution optical spectra, and new optical multifilter polarimetry and low resolution optical spectra spanning an interval of a decade and a broad range of precessional and orbital phases. We derive $text{E(B-V)}=0.86pm0.10$ and revised UV and U band polarizations and polarization angles that yield the same position angle as the optical. The polarization wavelength dependence is consistent with optical-dominating electron scattering with a Rayleigh component in U and the UV filters; no polarization changes were observed during a flare event. Using profile orbital and precessional modulation of multiple lines we derive properties for the accretion disk, present evidence for a strong disk wind, determine its velocity structure, and demonstrate its variability on timescales unrelated to the orbit. We derive a mass ratio $q=0.37pm0.04$, and masses $text{M}_X=4.2pm0.4 text{M}_odot$, $text{M}_A=11.3pm 0.6 text{M}_odot$, and show that the A star fills its Roche surface. The O I 7772 r{A} and 8446 r{A} lines show different but related orbital modulation and no evidence for a circumbinary disk component. Instead, the spectral line profile variability can be understood with an ionization stratified outflow predicted by thermal wind modeling, which also accounts for an extended equatorial structure detected at long wavelength.
Microquasars occasionally exhibit massive jet ejections which are distinct from the continuous or quasi-continuous weak jet ejections. Because those massive jet ejections are rare and short events, they have hardly been observed in X-ray so far. In this paper, the first X-ray observation of a massive jet ejection from the microquasar SS 433 with the Rossi X-ray Timing Explorer (RXTE) is reported. SS 433 undergoing a massive ejection event shows a variety of new phenomena including a QPO-like feature near 0.1 Hz, rapid time variability, and shot-like activities. The shot-like activity may be caused by the formation of a small plasma bullet. A massive jet may be consist of thousands of those plasma bullets ejected from the binary system. The size, mass, internal energy, and kinetic energy of the bullets and the massive jet are estimated.
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