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

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.

The origin of radio emission from radio-quiet active galactic nuclei

“…RQ AGN have shown cm/mm-band variability on daymonth-year timescales (e.g., Wrobel 2000; Chatterjee et al 2009;Mundell et al 2009;Baldi et al 2015), which, at face value, appears to be similar to the behaviour of binaries in their hard states. Nevertheless, simultaneous radio/X-ray monitorings are rare and have so far yielded only weak or no correlations, with ambiguous results (see Figure 6, Bell et al 2011;King et al 2011King et al , 2013Jones et al 2011Jones et al , 2017.…”

Simultaneous Millimetre-wave and X-ray monitoring of the Seyfert galaxy NGC 7469

“…However, in order to truly test the connection between the mm-wave and X-ray sources of RQ AGN, simultaneous monitoring is essential. Diligent attempts at 5 and 8.5 GHz, either focus on more RL objects (Bell et al 2011), or meet limited success in RQ ones (Jones et al 2017). No such campaign, as far as we know, exists for higher frequencies.…”

Unravelling the origin of extended radio emission in narrow-line Seyfert 1 galaxies with the JVLA

“…They argue that in most cases the jet loses most of its power within the innermost kiloparsec. Jones et al (2017) study the radio variability of J1203+4431 but find no significant signs of it. They hypothesise that the jet-like structure results from an earlier period of higher activity, and that at the moment the source is at a low-activity state.…”

“…Very high-resolution observations with the VLBA at 1.7 GHz (Doi et al 2013) and with the JVN at 22 GHz (Doi et al 2015) do not detect the source. Several studies have suggested that the origin of the inner structure is the AGN activity (e.g., Gallimore et al 2006;Maitra et al 2011;Jones et al 2017). Based on broadband SED modelling Maitra et al (2011) conclude that the source hosts a mildly relativistic jet/outflow.…”