Magnetic Field Strengths in the Hot Spots and Lobes of Three Powerful Fanaroff‐Riley Type II Radio Sources

Abstract

We have made deep Chandra observations of three powerful FRII radio sources: two quasars (3C 263 and 3C 351) and one radio galaxy (3C 330). X-ray emission from hotspots and lobes, as well as from the active nucleus, is detected in each source.We model the hotspots' synchrotron spectra using VLA, BIMA and Hubble Space Telescope data. In 3C 263 and 3C 330, the hotspots' X-ray emission is at a level consistent with being synchrotron self-Compton (SSC) emission, with a hotspot magnetic field close to the equipartition value. In the two hotspots of 3C 351, however, an SSC origin for the X-rays would require the magnetic field strength to be an order of magnitude below the equipartition value in our models: in addition, there are offsets between the radio, optical and X-ray emission from the secondary hotspot which are hard to explain in a simple SSC model. We discuss the emission mechanisms that may be responsible for these observations. On our preferred model, the X-ray emission from the radio lobes of the three sources is due to inverse-Compton scattering of the microwave background radiation. If this is the case, the magnetic field strengths in the lobes are typically about a factor -2 -2 below the equipartition values, assuming uniform lobe electron and magnetic field distributions.We detect extended X-ray emission, which we attribute to a cluster/group environment, around 3C 263 and 3C 330. This detection allows us to show that the lobes are close to pressure balance with their surroundings, as long as no non-radiating particles contribute to the internal pressure of the lobes.Subject headings: galaxies: active -X-rays: galaxies -X-rays: quasars -radiation mechanisms: non-thermal ROSAT observations of the archetypal FRII object Cygnus A (Harris, Carilli & Perley 1994) showed that the X-ray emission from its hotspots was consistent with the SSC process if the magnetic field strength was close to the equipartition or minimum-energy values (Burbidge 1956). This result is often taken as evidence for equipartition between magnetic fields and synchrotronemitting electrons in radio sources in general. Other ROSAT observations, however (e.g., Harris, Leighly & Leahy 1998), showed that some hotspots had X-ray emission too bright to be produced by the SSC mechanism with equipartition field strengths, suggesting that a different emission process was responsible. At the time of writing, after a number of new Chandra hotspot detections, this dichotomy remains, as shown in Table 1. Three interesting facts about this division are immediately apparent. Firstly, the number of objects whose emission processes are not from SSC near equipartition (hereafter 'non-SSCE' objects) is still a significant fraction of the total. Secondly, the non-SSCE objects all display broad emission lines, which may, after all, indicate some role for beaming in the hotspots. And, thirdly, the non-SSCE objects all have optical synchrotron hotspots.The major remaining questions in this area are therefore:1. Are magnetic field strengths close to equipartit...

RAiSE III: 3C radio AGN energetics and composition

“…Hardcastle et al 2002;Croston et al 2004Croston et al , 2005Ineson et al 2017). In this technique the X-ray emission upscattered from the synchrotronemitting electrons is compared to that expected if their energy densities are in equipartition with the magnetic field.…”

A Multiwavelength Study of the High Surface Brightness Hot Spot in PKS 1421–490

“…The simple one-zone model with a near equipartition magnetic field strength provides a good description of the available data. Hardcastle et al (2002) used more complicated spectral and spatial models for three sources, and found that this did not have a significant effect on the derived plasma parameters. We are therefore confident in our parameter estimates using this "first-order" one-zone model.…”

Synthetic Observations of Simulated Radio Galaxies. I. Radio and X‐Ray Analysis

“…Brunetti et al (1999) and reported the detection of X-ray emission in the lobes of 3C 219 and in 3C 215 and 3C 334, respectively, that possibly arises from inverse Compton scattering of IR photons from the quasar nucleus. IC/3K lobe emission has been reported in several radio galaxies, including Fornax A (Kaneda et al 1995;Feigelson et al 1995), Centaurus B (Tashiro et al 1998), A0038À096 (Bagchi, Pislar, & Neto 1998), 3C 295 (Brunetti et al 2001), 3C 330 (Hardcastle et al 2002), and 3C 263 (Crawford & Fabian 2003). Synchrotron self-Compton (SSC) emission was reported in the hot spots of several powerful galaxies, including Cygnus A (Harris, Carilli, & Perley 1994), 3C 295 (Harris et al 2000), 3C 273 (Röser et al 2000), 3C 123 (Hardcastle, Birkinshaw, & Worrall 2001), 3C 207 , and 3C 263 and 3C 330 (Hardcastle et al 2002).…”