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

• Published in: The Astrophysical journal Vol. 858; no. 1; pp. 27 - 43
• Main Authors: Zhang, Jin, Du, Shen-shi, Guo, Sheng-Chu, Zhang, Hai-Ming, Chen, Liang, Liang, En-Wei, Zhang, Shuang-Nan
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.05.2018; IOP Publishing
• Subjects: Active galactic nuclei; Astrophysics; Cosmic microwave background; Energy; galaxies: active; galaxies: jets; High energy astronomy; Knots; Luminosity; Radiation; radiation mechanisms: non-thermal; Radio emission; Synchrotron radiation; X ray spectra; X-ray emissions; X-rays: galaxies
• DOI: 10.3847/1538-4357/aab9b2
• ISSN: 0004-637X

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 1 hotspot and 22 knots is well explained as synchrotron radiation 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 process, but the derived jet powers (Pjet) are not correlated with Lk and most of them are larger than Lk, with more than three orders of magnitude, where Lk 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 for the cosmic microwave background photons (IC/CMB). In this scenario, the derived Pjet of knots and hotspots are correlated with and comparable to Lk. These results suggest that the IC/CMB model may be a promising interpretation of the X-ray emission. In addition, a tentative knot-hotspot sequence in the synchrotron peak-energy-peak-luminosity plane is observed, similar to the blazar sequence, which may be attributed to the different cooling mechanisms of electrons.