PG1004+130: Hybrid Morphology Source or a Restarted FRII? A uGMRT Polarimetric Investigation

TL;DR

This study uses uGMRT polarimetric imaging to analyze PG1004+130, revealing it as a restarted FRII-type quasar with complex magnetic fields, spectral properties, and evidence of plasma mixing and turbulence in its lobes.

Contribution

First detailed polarimetric and spectral analysis of PG1004+130 confirming its restarted FRII morphology and magnetic field structure, with insights into plasma turbulence and activity history.

Findings

Detected polarization in core, jets, and lobes.

Identified spectral index variations indicating multiple activity episodes.

Estimated plasma mass and turbulence in lobes.

Abstract

We present here the polarization image of the hybrid morphology (HYMOR) and broad-absorption line (BAL) quasar PG1004+130 at 694~MHz obtained with the upgraded Giant Metrewave Radio Telescope (uGMRT). We detect linear polarization in this source's core, jets, and lobes. The visible discontinuity in total intensity between the inner jets and the kpc-scale lobes suggests that the source is restarted. The inferred poloidal magnetic (B-) field structure in the inner jet is consistent with that observed in Fanaroff-Riley (FR) type II sources, as are the B-fields aligned with the lobe edges. Moreover, archival Chandra and XMM-Newton data indicate that PG1004+130 displays several FRII-jet-like properties in X-rays. We conclude that PG1004+130 is a restarted quasar, with both episodes of activity being FRII type. The spectral index images show the presence of an inverted spectrum core ($\alpha=+0.30\pm0.01$), a steep spectrum inner jet ($\alpha=-0.62\pm0.06$) surrounded by much steeper lobe emission ($\alpha\approx-1.2\pm0.1$), consistent with the suggestion that the lobes are from a previous activity episode. The spectral age difference between the two activity episodes is likely to be small ($<1.2 \times 10^7$ years), in comparison to the lobe ages ($\sim 3.3\times 10^7$ years). The inferred B-fields in the lobes are suggestive of turbulence and the mixing of plasma. This may account for the absence of X-ray cavities around this source, similar to what is observed in M87's radio halo region. The depolarization models reveal that thermal gas of mass $\sim (2.4\pm0.9)\times 10^9$ M$_\odot$ is mixed with the non-thermal plasma in the lobes of PG1004+130.