The resolved jet of 3C 273 at 150 MHz

TL;DR

This study presents the first sub-arcsecond low-frequency images of quasar 3C 273 at 150 MHz, revealing jet structures, absorption effects, and constraining jet power, speed, and inclination with high-resolution LOFAR observations.

Contribution

It provides the first high-resolution low-frequency images of 3C 273, demonstrating LOFAR's capability to image complex sources and analyzing jet properties at MHz frequencies.

Findings

Jet kinetic power estimated between 3.5×10^43 and 1.5×10^44 erg/s.

Absorption effects (FFA and SSA) are present in the emission.

Counter-jet remains undetected, setting brightness limits.

Abstract

Since its discovery in 1963, 3C273 has become one of the most widely studied quasars with investigations spanning the electromagnetic spectrum. While much has been discovered about this historically notable source, its low-frequency emission is far less well understood. Observations in the MHz regime have traditionally lacked the resolution required to explore small-scale structures that are key to understanding the processes that result in the observed emission. In this paper we use the first sub-arcsecond images of 3C273 at MHz frequencies to investigate the morphology of the compact jet structures and the processes that result in the observed spectrum. Using the full complement of LOFAR's international stations, we produce $0.31 \times 0.21$ arcsec images of 3C273 at 150 MHz to determine the jet's kinetic power, place constraints on the bulk speed and inclination angle of the jets, and look for evidence of the elusive counter-jet at 150 MHz. Using ancillary data at GHz frequencies, we fit free-free absorption (FFA) and synchrotron self-absorption (SSA) models to determine their validity in explaining the observed spectra. The images presented display for the first time that robust, high-fidelity imaging of low-declination complex sources is now possible with the LOFAR international baselines. We show that the main small-scale structures of 3C273 match those seen at higher frequencies and that absorption is present in the observed emission. We determine the kinetic power of the jet to be in the range of $3.5 \times 10^{43}$ - $1.5 \times 10^{44}$ erg s$^{-1}$ which agrees with estimates made using higher frequency observations. We derive lower limits for the bulk speed and Lorentz factor of $\beta \gtrsim 0.55$ and $\Gamma \geq 1.2$ respectively. The counter-jet remains undetected at $150$ MHz, placing a limit on the peak brightness of $S_\mathrm{cj\_150} < 40$ mJy beam$^{-1}$.