Continuum reverberation mapping in a z = 1.41 radio-loud quasar

Q0957+561 was the first discovered gravitationally lensed quasar. The mirage shows two images of a radio-loud quasar at redshift z = 1.41. The time lag between these two images is well established around one year. We detected a very prominent variation in the optical brightness of Q0957+561A at the beginning of 2009, which allowed us to predict the presence of significant intrinsic variations in multi-wavelength light curves of Q0957+561B over the first semester of 2010. To study the predicted brightness fluctuations of Q0957+561B, we conducted an X-ray, NUV, optical and NIR monitoring campaign using both ground-based and space-based facilities. The continuum NUV-optical light curves revealed evidence of a centrally irradiated, standard accretion disk. In this paper, we focus on the radial structure of the standard accretion disk and the nature of the central irradiating source in the distant radio-loud active galactic nucleus (AGN).The authors thank Harvey Tananbaum and Neil Gehrels for granting Director’s Discretionary Time for the Chandra and Swift observations, respectively. We also thank the operations group of the Liverpool Telescope (Robert Smith and Jon Marchant) for their kind interaction and support during our ground-based monitoring projects. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canarias with financial support from the UK Science and Technology Facilities Council. This research has been supported by the Spanish Department of Science and Innovation grants ESP2006-13608-C02-01 and AYA2010- 21741-C03-03 (Gravitational LENses and DArk MAtter - GLENDAMA project), and University of Cantabria funds