Accretion Onto the Supermassive Black Hole in the High-redshift Radio-loud AGN 0957+561

TL;DR

This study uses multiwavelength monitoring of the gravitationally lensed AGN 0957+561 to investigate accretion processes and the origin of X-ray emission, revealing delays and reprocessing in the accretion disk and jet base.

Contribution

It provides the first reverberation mapping analysis of a high-redshift radio-loud AGN, identifying the X-ray source location and accretion disk structure.

Findings

UV/optical variability consistent with thermal reprocessing near the black hole

X-ray emission delayed by about 32 days, indicating a jet base origin

Absence of X-ray reflection features supports a jet-based X-ray source

Abstract

We present the results of our X-ray, UV and optical monitoring campaign of the first gravitationally lensed AGN from late 2009 to mid 2010. The trailing (B) image of the AGN 0957+561 shows the intrinsic continuum variations that were predicted in advance based on observations of the leading (A) image in the gr optical bands. This multiwavelength variability of the B image allows us to carry out a reverberation mapping analysis in the radio-loud AGN 0957+561 at redshift z = 1.41. We find that the U-band and r-band light curves are highly correlated with the g-band record, leading and trailing it by 3 +/- 1 days (U band) and 4 +/- 1 days (r band). These 1-sigma measurements are consistent with a scenario in which flares originated in the immediate vicinity of the supermassive black hole are thermally reprocessed in a standard accretion disk at about 10-20 Schwarzschild radii from the central dark object. We also report that the light curve for the X-ray emission with power-law spectrum is delayed with respect to those in the Ugr bands by about 32 days. Hence, the central driving source can not be a standard corona emitting the observed power-law X-rays. This result is also supported by X-ray reprocessing simulations and the absence of X-ray reflection features in the spectrum of 0957+561. We plausibly interpret the lack of reflection and the 32-day delay as evidence for a power-law X-ray source in the base of the jet at a typical height of about 200 Schwarzschild radii. A central EUV source would drive the variability of 0957+561.