Quasi-simultaneous observations of radio and X-ray variability in three radio-quiet Seyfert galaxies. Issue 2 (12th July 2022)

• Record Type: Journal Article
• Authors: Chen, Sina; Laor, Ari; Behar, Ehud
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 515:Issue 2(2022)
• Page Start: 1723
• Page End: 1735
• Publication Date: 2022-07-12
• Subjects: galaxies: active -- galaxies: nuclei -- galaxies: Seyfert -- radio continuum: galaxies -- X-rays: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1891
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Radio variability in some radio-quiet (RQ) active galactic nuclei suggests emission from regions close to the central engine, possibly the outer accretion disc corona. If the origins of the radio and the X-ray emission are physically related, their emission may be temporarily correlated, possibly with some time delays. We present the results of quasi-simultaneous radio and X-ray monitoring of three RQ Seyfert galaxies, Mrk 110, Mrk 766, and NGC 4593, carried out with the Very Large Array at 8.5 GHz over a period of about 300 d, and with the Rossi X-ray Timing Explorer at 2–10 keV over a period of about 2000 d. The radio core variability is likely detected in the highest resolution (A configuration) observations of Mrk 110 and NGC 4593, with a fractional variability amplitude of 6.3 per cent and 9.5 per cent, respectively. A cross-correlation analysis suggests an apparently strong (Pearson r = −0.89) and highly significant correlation ( p = 1 × 10 −6 ) in Mrk 110, with the radio lagging the X-ray by 56 d. However, a further analysis of the r values distribution for physically unrelated long time delays reveals that this correlation is not significant. This occurs since the Pearson correlation assumes white noise, while both the X-ray and the radio light curves follow red noise, which dramatically increases the chance, by a factor of ∼10 3, to get extremely high r values in uncorrelated data sets. A significantly longer radio monitoring with a higher sampling rate, preferably with a high-resolution fixed radio array, is required in order to reliably detect a delay.