Examining the High-energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets

Abstract

We compile the radio-optical-X-ray spectral energy distributions (SEDs) of 65 knots and 29 hotspots in 41 active galactic nucleus jets to examine their high energy radiation mechanisms. Their SEDs can be fitted with the single-zone leptonic models, except for the hotspot of Pictor A and six knots of 3C 273. The X-ray emission of one hotspot and 22 knots is well explained as synchrotron radiations under the equipartition condition; they usually have lower X-ray and radio luminosities than the others, which may be due to a lower beaming factor. An inverse Compton (IC) process is involved for explaining the X-ray emission of the other SEDs. Without considering the equipartition condition, their X-ray emission can be attributed to the synchrotron-self-Compton (SSC) process, but the derived jet power (P jet ) are not correlated with L k and most of them are larger than L k with more than three orders of magnitude, where L k is the jet kinetic power estimated with their radio emission. Under the equipartition condition, the X-ray emission is well interpreted with the IC process to the cosmic microwave background photons (IC/CMB). In this scenario, the derived P jet of knots and hotspots are correlated with and comparable to L k . These results suggest that the IC/CMB model may be the promising interpretation of their X-ray emission. In addition, a tentative knot-hotspot sequence in the synchrotron peak-energypeak-luminosity plane is observed, similar to the blazar sequence, which may be attributed to their different cooling mechanisms of electrons.

Jet Properties of Compact Steep-Spectrum Sources and an Eddington-Ratio-Driven Unification Scheme of Jet Radiation in Active Galactic Nuclei

“…For the extended regions, the derived values of γ b , B, and p 1 are consistent with the values of substructures in large-scale jets, as displayed in Figure 5, where the data of these large-scale jet knots and hotspots are taken from Zhang et al (2018b). The derived γ b values of the large-scale extended regions in CSSs cluster at the lower end of the γ b distribution.…”

“…The radio emission in ∼0.01-10 GHz in the SEDs should not be dominated by the emission of the compact core because of a significant synchrotron-self-absorption effect on the radio emission from the core region. It would be attributed to the emission from the large-scale extended regions, similar to large-scale hotspots and knots (e.g., Zhang et al 2010Zhang et al , 2018b. Therefore, we employ a two-zone leptonic radiation model to fit the constructed SEDs.…”

Deciphering the Origin of the GeV--TeV Gamma-ray Emission from SS 433

“…M87 and 3C 273 are very bright radio galaxies, and the broadband spectra and velocities of their knots are observed. For M87, the knots in the 10-100 pc scale have soft X-ray spectra without a cutoff feature (Zhang et al 2018). Their intrinsic velocity is estimated to be Γβ ∼ 0.3−10 with a possible velocity stratification (Park et al 2019).…”

“…According to Zhang et al (2018), the peak frequency of the synchrotron spectrum and the magnetic field strength in X-ray knots and hotspots in radio galaxies are estimated to be ν pk ∼ 10 9 − 10 17 Hz and B ∼ 10 − 300 µG, respectively. The radio, optical, and X-ray spectra for some knots are inconsistent with a single component synchrotron emission.…”

Discovery of Candidate X-ray Jets in High-Redshift Quasars

“…The Galactic column density was fixed equal to values from Dickey & Lockman (1990). We also fixed the photon index to Γ = 1.9, which we in- ferred to be a standard slope for X-ray jet and knot spectra (e.g., Marshall et al 2002;Siemiginowska et al 2002;Schwartz et al 2006a,b;Goodger et al 2010;Zhang et al 2018). The observed 0.5-7.0 keV X-ray jet fluxes are shown in Table 5.…”