Testing thermal reprocessing in AGN accretion discs

TL;DR

This paper tests the thermal reprocessing hypothesis in AGN accretion discs by analyzing wavelength-dependent time delays and spectral data, estimating key parameters, and discussing implications for the model and cosmology.

Contribution

It provides observational evidence and modeling of wavelength-dependent delays in AGN, estimating physical parameters and challenging current cosmological distance measures.

Findings

Time delays increase with wavelength as predicted by reprocessing.

Estimated H_0 from the model is lower than accepted values.

Model fits suggest nuclear reddening and black hole accretion parameters.

Abstract

The thermal reprocessing hypothesis in AGN, where EUV/X-ray photons are reprocessed by the accretion disc into optical/UV photons, predicts wavelength-dependent time delays between the optical continuum at different wavelengths. Recent photometric monitoring by Sergeev et al. has shown that the time-delay is observed in 14 AGN, and generally seen to increase with increasing wavelength, as predicted in the reprocessing scenario. We fit the observed time delays and optical spectral energy distribution using a disc reprocessing model. The model delivers estimates for the nuclear reddening, the product of black hole mass times accretion rate, and the distance to each object. However, the distances at face value give H_0 = 44 +/- 5 km/s/Mpc - a factor of 1.6 smaller than generally accepted. We discuss the implications of this on the reprocessing model.