Gravitational lensing: strong; Polarization; Quasars: emission lines; Quasars: individual: Q957+561; Quasars: supermassive black holes; Astrophysical observatory; Polarization angle; Polarization observations; Polarization parameters; Polarization rates; Polarization vectors; Spectral characteristics; Spectral energy distribution; Astronomy and Astrophysics; Space and Planetary Science; astro-ph.GA
Abstract :
[en] Context. We present new spectroscopic and polarimetric observations of the first discovered gravitational lens, Q0957+561. The lensed quasar has been observed with the 6 m telescope of the Special Astrophysical Observatory (Russia) in polarimetric and spectroscopic modes. Aims. We explore the spectropolarimetric parameters of the A and B components of Q0957+561 to investigate the innermost structure of gravitationally lensed quasars and explore the nature of polarization in lensed quasars. Additionally, we aim to compare their present-day spectral characteristics with previous observations in order to study long-term spectral changes. Methods. We perform new spectral and polarization observations of the Q0957+561 A and B images. After observed data reduction, we analyse the spectral characteristics of the lensed quasar, comparing the spectra of the A and B images, as well as comparing previously observed image spectra with present-day ones. The polarization parameters of the two images are also compared. Furthermore, we model the macro-lens influence on the polarization of the images, representing the gravitational lens with a singular isothermal elliptical potential. Results. We find that the brightness and the spectral energy distribution ratio of components A and B have changed over a long period. Polarization in the broad lines of components A and B show that equatorial scattering cannot be detected in this lensed quasar. We find wavelength-dependent polarization that may be explained as a combination of the polarization from the disc and the outflowing material. There is a significant difference between the polarization parameters of the A and B images: The B component shows a higher polarization rate and polarization angle. However, both polarization vectors are nearly perpendicular to the observed radio jet projection. This indicates that the polarization in the continuum comes from the accretion disc. Our simple lensing model of a polarized source shows that, in principle, macro lenses can cause the observed differences in the polarization parameters of the Q0957+561A and B images. Using the Mg II broad line and luminosity of component A, we estimate the Q0957+561 black hole mass to be MSMBH ≈ (4.8-6.1) × 108 M·.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Popović, L.C.; Astronomical Observatory, Belgrade, Serbia ; Department of Astronomy, Faculty of Mathematics, University of Belgrade, Belgrade, Serbia
Afanasiev, V.L.; Special Astrophysical Observatory of the Russian As, Nizhnij Arkhyz, Karachaevo-Cherkesia, Russian Federation
Shablovinskaya, E.S. ; Special Astrophysical Observatory of the Russian As, Nizhnij Arkhyz, Karachaevo-Cherkesia, Russian Federation
Ardilanov, V.I.; Special Astrophysical Observatory of the Russian As, Nizhnij Arkhyz, Karachaevo-Cherkesia, Russian Federation
Savic, Djordje ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Space sciences, Technologies and Astrophysics Research (STAR) ; Astronomical Observatory, Belgrade, Serbia
Language :
English
Title :
Spectroscopy and polarimetry of the gravitationally lensed quasar Q0957+561
Acknowledgements. This work is supported by the Ministry of Education, Science and Technological Development of R. Serbia (the contract 451-03-68/2020-14/200002). VLA and ESS thank the grant of Russian Science Foundation project number 20-12-00030 “Investigation of geometry and kinematics of ionized gas in AGNs by polarimetry methods”, which supported the spectropo-larimetric and polarimetric observations and data analyze. Observations with the SAO RAS telescopes are supported by the Ministry of Science and Higher Education of the Russian Federation (including agreement No 05.619.21.0016, project ID RFMEFI61919X0016). We would like to thank the referee for giving very useful comments which helped improving the quality of the paper.