Revisiting the continuum reverberation lags in the AGN PKS 0558-504
Abstract
We present a revised analysis of the photometric reverberation mapping campaign of the narrow-line Seyfert 1 galaxy PKS 0558 - 504 carried out with the Swift Observatory during 2008-2010. Previously, Gliozzi et al. (2013) found using the Discrete Correlation Function (DCF) method that the short-wavelength continuum variations lagged behind variations at longer wavelengths, the opposite of the trend expected for thermal reprocessing of X-rays by the accretion disc, and they interpreted their results as evidence against the reprocessing model. We carried out new DCF measurements that demonstrate that the inverted lag-wavelength relationship found by Gliozzi et al. resulted from their having interchanged the order of the driving and responding light curves when measuring the lags. To determine the inter-band lags and uncertainties more accurately, we carried out new measurements with four independent methods. These give consistent results showing time delays increasing as a function of wavelength, as expected for the disc reprocessing scenario. The slope of the re-analysed delay spectrum appears to be roughly compatible with the predicted τ ∝ λ4/3 relationship for reprocessing by an optically thick and geometrically thin accretion disc, although the data points exhibit a large scatter about the fitted power-law trend.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- September 2022
- DOI:
- 10.1093/mnras/stac1945
- arXiv:
- arXiv:2207.02474
- Bibcode:
- 2022MNRAS.515.2890G
- Keywords:
-
- accretion;
- accretion disc;
- galaxies: active;
- galaxies: individual: PKS 0558 - 504;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 7 figures, 2 tables