Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism

TL;DR

This study uses Chandra X-ray observations to analyze the hotspot in radio galaxy 3C 445, exploring different emission mechanisms and challenging simple models by revealing spatial displacement and spectral features.

Contribution

It provides the first detailed X-ray imaging of 3C 445's hotspot and evaluates multiple emission models, highlighting the need for complex electron distributions and flow dynamics.

Findings

X-ray emission is displaced upstream and west of the radio-optical hotspot.

One zone models cannot reproduce the observed spectral energy distribution and displacement.

X-ray emission could be due to external Compton scattering or synchrotron from separate electron populations.

Abstract

We present new {\it Chandra} observations of the radio galaxy 3C 445, centered on its southern radio hotspot. Our observations detect X-ray emission displaced upstream and to the west of the radio-optical hotspot. Attempting to reproduce both the observed spectral energy distribution (SED) and the displacement, excludes all one zone models. Modeling of the radio-optical hotspot spectrum suggests that the electron distribution has a low energy cutoff or break approximately at the proton rest mass energy. The X-rays could be due to external Compton scattering of the cosmic microwave background (EC/CMB) coming from the fast (Lorentz factor $\Gamma\approx 4$) part of a decelerating flow, but this requires a small angle between the jet velocity and the observer's line of sight ($\theta\approx 14^{\circ}$). Alternatively, the X-ray emission can be synchrotron from a separate population of electrons. This last interpretation does not require the X-ray emission to be beamed.