A comprehensive long term study of the radio and X-ray Variability of NGC 4051 Paper II

TL;DR

This study re-analyzes radio and X-ray data of NGC 4051, finding no evidence of radio variability despite X-ray fluctuations, challenging previous claims and suggesting the radio structures are remnants of past activity.

Contribution

The paper provides a careful re-analysis of radio and X-ray variability in NGC 4051, emphasizing the importance of beam effects and offering a more accurate assessment of core radio flux.

Findings

No significant radio variability detected in NGC 4051.

Radio structures likely remnants of past activity, not current jets.

Contradicts previous claims of radio-X-ray anti-correlation.

Abstract

The origin of the low luminosity radio emission in radio-quiet AGN, is unknown. The detection of a positive correlation between the radio and X-ray emission would imply a jet-like origin, similar to that seen in `hard state' X-ray binary systems. In our previous work, we found no believable radio variability in the well known X-ray bright Seyfert 1 galaxy NGC 4051, despite large amplitude X-ray variability. In this study we have carefully re-analysed radio and X-ray observations using the same methods as our previous work, we again find no evidence for core radio variability. In direct contrast to our findings, another study claim significant radio variability and a distinctive anti-correlation between radio and X-ray data for the same source. The other study report only integral flux values and do not consider the effect of the changing array on the synthesised beam. In both our studies of NGC 4051 we have taken great care to account for the effect that the changing beam size has on the measured radio flux and as a result we are confident that our method gives more accurate values for the intrinsic core radio flux. However, the lack of radio variability we find is hard to reconcile because radio images of NGC 4051 do show jet-like structure. We suggest that the radio structures observed are likely the result of a previous period of higher radio activity and that the current level of radio emission from a compact nuclear jet is low.