Accretion onto the supermassive black hole in the high-redshift radio-loud AGN0957+561

Abstract

We present the results of our X-ray, UV, and optical monitoring campaign of the first gravitationally lensed active galactic nucleus (AGN) from late 2009 to mid-2010. The trailing (B) image of the AGN 0957+561 showsthe 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 1σ measurements are consistent with a scenario in which flares originated in the immediate vicinityof the supermassive black hole are thermally reprocessed in a standard accretion disk at ~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 theU gr bands by ~ 32 days. Hence, the central driving source cannotbe 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 ~ 200 Schwarzschild radii. A central EUV source would drive the variability of 0957+561.