Derivation of the physical parameters of the jet in S5 0836+710 from stability analysis

Abstract

Context. A number of extragalactic jets show periodic structures at different scales that can be associated with growing instabilities. The wavelengths of the developing instability modes and their ratios depend on the flow parameters, so the study of those structures can shed light on jet physics at the scales involved. Aims. In this work, we use the fits to the jet ridgeline obtained from different observations of S5 B0836+710 and apply stability analysis of relativistic, sheared flows to derive an estimate of the physical parameters of the jet. Methods. Based on the assumption that the observed structures are generated by growing Kelvin-Helmholtz (KH) instability modes, we have run numerical calculations of stability of a relativistic, sheared jet over a range of different jet parameters. We have spanned several orders of magnitude in jet-to-ambient medium density ratio, and jet internal energy, and checked different values of the Lorentz factor and shear layer width. This represents an independent method to obtain estimates of the physical parameters of a jet. Results. By comparing the fastest growing wavelengths of each relevant mode given by the calculations with the observed wavelengths reported in the literature, we have derived independent estimates of the jet Lorentz factor, specific internal energy, jet-toambient medium density ratio and Mach number. We obtain a jet Lorentz factor γ 12, specific internal energy of ε 10 −2 c 2 , jet-to-ambient medium density ratio of η ≈ 10 −3 , and an internal (classical) jet Mach number of M j ≈ 12. We also find that the wavelength ratios are better recovered by a transversal structure with a width of 10 % of the jet radius. Conclusions. This method represents a powerful tool to derive the jet parameters in all jets showing helical patterns with different wavelengths.

RadioAstron reveals a spine-sheath jet structure in 3C 273

“…The author reported an oscillation velocity of 0.5c, and a pattern speed of (0.070 ± 0.016)c. These velocities, clearly smaller than the flow speed revealed by, e.g., the strong brightness asymmetry, show that the observed structures are caused by waves that propagate through the jet (i.e. helical patters, see Perucho et al 2012;Cohen et al 2015;Vega-García et al 2019). The wavelengths that can be derived from the RA observations reported there coincide with those given in Lobanov & Zensus (2001), plus a further, longer wavelength of 50 mas, due to the sensitivity achieved at larger scales.…”

Inverse Compton Scattering of Radiation from a Central Source as a Possible Mechanism for the Formation of X-Ray Radiation from Kiloparsec Jets of Core-Dominated Quasars

“…The possibility of such a deviation from equipartition for kpc-scale jets was noted by Mehta et al (2009). An extremely high brightness temperature, exceeding the maximum permissible value under the equipartition condition excluding the Compton catastrophe, was detected by the ground-space radio interferometer RadioAstron for several active nuclei (Gómez et al 2016;Kutkin et al 2018;Pilipenko et al 2018;Vega-García et al 2019;Kravchenko et al 2020), including 3C 273 (Kovalev et al 2016). This result can be explained either by the large (∼ 100) Doppler factor of the pc-scale jets, or by the fact that the energy density of the emitting particles is higher than the energy density of the magnetic field even in the pc-scale.…”

Jet collimation in NGC 315 and other nearby AGN

“…In this final section we discuss the possible impact that a more or less prominent disk-launched jet may have on the long-term jet stability and evolution. A surrounding jet sheath 7 , characterized by a smaller sound speed with respect to the central hot spine, provides further stability to relativistic outflows due to the increase in the jet inertia and the drop in instability growth rates (Hardee & Rosen 2002;Hardee & Hughes 2003;Perucho et al 2005Perucho et al , 2019Hardee 2007;Perucho & Lobanov 2007;Mizuno et al 2007;Vega-García et al 2019). Furthermore, its presence mitigates the impact of surface perturbations that can be induced by the penetration of stars (which has been recently appointed as a possible triggering mechanism for jet deceleration of FRI jets, see Perucho 2020), since its smaller sound speed implies a slower propagation of the turbulent layer toward the jet axis.…”