Probing AGN with spectropolarimetry: accretion disk and SMBH parameters

The interaction of a supermassive black hole with the matter of an accretion disk in the presence of a magnetic field is the key mechanism of energy release in active galactic nuclei. However, determining the physical parameters of this system, such as the spin and mass of the black hole, the shape and parameters of the rotation of the accretion disk, and the geometry of the magnetic field in the accretion disk is a complex and not completely solved problem. We have previously shown, based on our numerical models, that these estimates can be obtained from just three parameters: the black hole mass, bolometric luminosity, and optical polarization. In this paper, we estimate the accretion disk and black hole parameters for a sample of 14 type 1 Seyfert galaxies. Using the spectropolarimetric data obtained by us, we selected only those objects in which the polarization of optical radiation is generated mainly by the mechanism in the accretion disk. Despite the small statistics, our results for such a sample are consistent with our previous conclusions and show a discrepancy between the disk magnetic field parameters and the classical Shakura-Sunyaev disk model.Comment: 9 pages, 5 figure

Spectroscopy and polarimetry of the gravitationally lensed quasar Q0957+561

We present new spectroscopic and polarimetric observations of the first discovered gravitational lens Q0957+561 obtained with the 6m telescope of the Special Astrophysical Observatory (SAO, Russia). We explore spectropolarimetric parameters of Q0957+561 A,B components to investigate the innermost structure of the quasar, and explore the nature of polarization in lensed quasars. Additionally, we compare their present-day spectral characteristics with previous observations in order to study long-term spectral changes. We analyze spectral characteristics of lensed quasar comparing spectra of A and B images, as well as comparing previously observed image spectra with present-day ones. The polarization parameters of A-B images are compared. We also model the macro-lens influence on the polarization of the images representing the gravitational lens with a singular isothermal elliptical potential. We find that the brightness and SED ratio of components A and B changed during a long period. Polarization in broad lines of components A and B showed that the equatorial scattering cannot be detected in this quasar. We find wavelength-dependent polarization that may be explained as a combination of the polarization from the disc and outflowing material. There is a significant difference between polarization parameters of the A and B images: the B component shows a higher polarization degree and polarization angle. However, both polarization vectors are nearly perpendicular to the observed radio jet projection. It indicates that the polarization in the continuum is coming from the accretion disc. Our simple lensing model of a polarized source showed that macro-lens can cause the observed differences in polarization parameters of Q0957+561 A,B images. Using Mg II broad line and luminosity of component A we estimated that the Q0957+561 black hole mass is M~(4.8-6.1) $10^8$ M$\odot$Comment: accepted in A

Small telescopes being effective: MAGIC or not?

The paper describes the MAGIC multi-mode focal reducer (Monitoring of Active Galaxies by Investigation of their Cores), commissioned on the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in September 2020. Three observational modes are currently realised: photometry, polarimetry, and long-slit spectroscopy. Reducing the focal length makes it possible to obtain a sufficiently large field of view for photometry and a large slit height for spectroscopy of $\sim$12$'$, as well as a large field of view for polarimetry with a quadrupole Wollaston prism of $\sim$6$'$.4. This feature makes the complex study of extended nebulae and galaxies efficient. The MAGIC capabilities are presented in examples of observations of various astronomical objects. The spectral mode in the range of 4000-7200 AA provides the spectral resolution $R \sim$ 1000; for a starlike target up to 14 mag in medium-band filters with a seeing of 1$''$ for 20 minutes of total exposure, the photometry accuracy is better than 0.01 mag and the polarization accuracy is better than 0.6%. Especially for the new focal reducer, an offset guide and a position angle rotation system were implemented. The results of the modernization of the baffle system in the optical scheme of the telescope for the suppression of scattered light are also described

Spectroscopy and polarimetry of the gravitationally lensed quasar Q0957+561

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⊙

Optical counterparts of two candidate ultraluminous x-ray sources in NGC 4536

Archival XMM-Newton, Chandra, and Hubble Space Telescope(HST) data have been used to study the X-ray and optical properties of two candidate ultraluminous X-ray sources in NGC 4536. In order to search for potential optical counterparts, relative astrometry between Chandra and HST was improved, and as a result, optical counterparts were detected for both X-ray sources. To complement our findings (based on the archival data), ground-based optical spectra of the counterparts were obtained with the 6-m BTA (Big Telescope Alt-azimuth) Telescope located at the Special Astrophysical Observatory. The calculated redshift (z = 0.4391 ± 0.0010) for one of the sources (X-3) indicates that the source is, in fact, a background active galactic nucleus. Two possible optical counterparts (s1 and s2) were found for X-2. Whether s1 is point-like or an extended source is unclear: If it is point-like and the emission is dominated by the donor, its spectral type indicates O-B star. The second source (s2) is point-like and is consistent with the colours and absolute magnitudes of a red supergiant