Multiwavelength power-spectrum analysis of NGC 5548. Issue 2 (28th September 2020)

• Record Type: Journal Article
• Authors: Panagiotou, C; Papadakis, I E; Kammoun, E S; Dovčiak, M
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 499:Issue 2(2020)
• Page Start: 1998
• Page End: 2006
• Publication Date: 2020-09-28
• Subjects: galaxies: active -- galaxies: individual: NGC 5548 -- galaxies: nuclei -- galaxies: Seyfert; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2920
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: NGC 5548 was recently monitored intensively from NIR to X-rays as part of the STORM campaign. Its disc emission was found to lag behind the observed X-rays, while the measured time lag was increasing with wavelength. These results are consistent with the assumption that short-term variability in AGN emission is driven by the X-ray illumination of the accretion disc. In this work, we studied the power spectrum of UV/optical and X-ray emission of NGC 5548, using the data of the STORM campaign as well as previous Swift data, in order to investigate the relation between the UV/optical and X-ray variability and to examine its consistency with the above picture. We demonstrate that even the power spectrum results are compatible with a standard disc being illuminated by X-rays, with low accretion rates, but the details are not entirely consistent with the results from the modelling of the 'τ versus λ' relation. The differences indicate that the inner disc might be covered by a 'warm corona' which does not allow the detection of UV/optical emission from the inner disc. Finally, we found strong evidence that the UV emission of NGC 5548 is not stationary.