DeepChandraobservations of Pictor A

Abstract

We report on deep Chandra observations of the nearby broad-line radio galaxy Pictor A, which we combine with new Australia Telescope Compact Array (ATCA) observations. The new X-ray data have a factor 4 more exposure than observations previously presented and span a 15-year time baseline, allowing a detailed study of the spatial, temporal and spectral properties of the AGN, jet, hotspot and lobes. We present evidence for further time variation of the jet, though the flare that we reported in previous work remains the most significantly detected time-varying feature. We also confirm previous tentative evidence for a faint counterjet. Based on the radio through X-ray spectrum of the jet and its detailed spatial structure, and on the properties of the counterjet, we argue that inverse-Compton models can be conclusively rejected, and propose that the X-ray emission from the jet is synchrotron emission from particles accelerated in the boundary layer of a relativistic jet. For the first time, we find evidence that the bright western hotspot is also time-varying in X-rays, and we connect this to the small-scale structure in the hotspot seen in high-resolution radio observations. The new data allow us to confirm that the spectrum of the lobes is in good agreement with the predictions of an inverse-Compton model and we show that the data favour models in which the filaments seen in the radio images are predominantly the result of spatial variation of magnetic fields in the presence of a relatively uniform electron distribution.

RAiSE III: 3C radio AGN energetics and composition

“…w > 2) is inconsistent with our estimates at the 2σ level. The comparison of our dynamical model based jet power and equipartition factor estimates to independent measurements from Hardcastle et al (2016) and Ineson et al (2017) have yielded the same outcome: a proton-to-lepton ratio of w < 2 at the 2σ level. There is therefore strong evidence against an energetically dominant population of relativistic protons or thermal plasma (i.e.…”

ALMA polarization observations of the particle accelerators in the hotspot of the radio galaxy 3C 445

“…Tingay et al (2008) suggested that X-rays in Pictor A are produced by synchrotron emission from compact pc-scale transient regions of enhanced magnetic field. This is consistent also with the recent discovery of temporal variability of the X-ray emission in the hot spot of Pictor A (Hardcastle et al 2016). An important result obtained by our ALMA observations of the hot spot 3C 445 South is the lack of significant polarization between E and W and in the diffuse emission located to the north of the polarized emission and visible up to the optical I-, R-, and B-band (Orienti et al 2012).…”

A non cool-core 4.6-keV cluster around the bright nearby radio galaxy PKS B1416−493

“…Given the relatively small source size, predictions for X-ray inverse-Compton radiation are dominated by the synchrotron self-Compton process, but the field strength would need to be almost 100 times below the equipartition value of 14 nT to match observations, with an implausible increase in total energy. Instead it is more likely that the X-rays are synchrotron, as inferred to be common in jet knots of FR I radio galaxies , found not unusual in FR II radio galaxies (e.g., Kraft et al 2005;Kataoka et al 2008;Hardcastle et al 2016), and favoured for some quasar jets (e.g., Jester et al 2007;Cara et al 2013;Meyer et al 2015). The precise characteristics of the radio to X-ray spectrum cannot be determined in the absence of high-resolution observations at intermediate frequencies, but we can infer that the spectral break needs to be ∆α > 0.5 to accommodate the measured value of αr and the interpolated value of αrx, and ∆α = 0.7 is adopted in Figure 10.…”