Optical Detection and Analysis of Pictor A's Jet

TL;DR

This study reports the first optical detection of knots in Pictor A's jet, supporting the existence of a second high-energy electron population and providing new insights into jet emission mechanisms.

Contribution

It presents the first optical imaging of Pictor A's jet knots, revealing evidence for a second electron population responsible for high-energy emissions.

Findings

Optical knots detected at 1600nm, 814nm, and 475nm wavelengths.

Localized particle re-acceleration likely causes the knots.

Electrons responsible for optical emission cannot account for X-ray flux.

Abstract

New images from the Hubble Space Telescope of the FRII radio galaxy Pictor A reveal a number of jet knot candidates which coincide with previously detected radio and x-ray knots. Previous observations in x-ray and radio bands show the entire jet to be 1.9' long, with interesting variability, but an optical component was previously unknown. The discovered optical component is faint, and knot candidates must be teased out from a bright host galaxy. Using three broadband filters, we extract knot fluxes and upper-bounds on the flux for multiple knot candidates at wavelengths of 1600nm, 814nm and 475nm. We find that the data suggest that localized particle re-accleration events followed by synchrotron emission could explain the observed knot candidates, but those electrons could not supply enough x-ray flux to match prior observations. Our data provide key evidence suggesting a second, higher energy electron population which was previously hypothesized, but could not be confirmed.