arXiv subjects

Đorđe Savić

Publications and source records attributed to Đorđe Savić.

9 recordsLinked to original sources

arXiv2026

A Meta-Learning Framework for Multitask Reverberation Mapping in Active Galactic Nuclei

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) is expected to observe active galactic nuclei (AGN) at sky densities of approximately 1000-4000 per sq. deg, enabling photometric reverberation mapping on an unprecedented scale. We present a meta-learning framework for AGN photometric reverberation mapping based on Attentive Latent Neural Processes (ALNP), developed by the SER-SAG-S1 directable software in-kind team for LSST. The framework clusters AGN light curves with similar topologies using Self-Organizing Maps and combines ALNPs with Mixture Density Models to learn light-curve structure, supermassive black hole (SMBH) properties, and accretion-disk transfer functions in an unsupervised manner. We evaluate the framework on simulated AGN light curves spanning a range of cadences and transfer functions, as well as on real data from the Zwicky Transient Facility. The learned latent representations encode information on both transfer functions and SMBH parameters. Relative to ensemble-trained baseline regressors, including Gaussian-process models, the framework improves light-curve reconstruction by 60-70%. The transfer function recovery improves by approximately 35% relative to the training prior in a low-variability cluster, while recovery of intrinsic SMBH and red-noise parameters improves by approximately 34%. We further demonstrate that models trained on simulated data can be applied to real AGN light curves. These results indicate that ALNP-based representations provide a flexible and scalable approach to photometric reverberation mapping and are well suited to the diverse AGN population expected from LSST and future time-domain surveys.

astro-ph.GA↗

arXiv2024

Size and kinematics of the low-ionization broad emission line region from microlensing-induced line profile distortions in gravitationally lensed quasars

MgII or H$α$ line profile distortions observed in five gravitationally lensed quasars have been compared with simulated ones. The simulations are based on three BLR models, a Keplerian disk (KD), an equatorial wind (EW), and a polar wind (PW). We find that the wide variety of observed line profile distortions can be reproduced with microlensing-induced distortions of line profiles generated by our BLR models. For three quasars, the most likely model is either KD or EW, depending on the orientation of the magnification map with respect to the BLR axis. This shows that the line profile distortions depend on the position and orientation of the BLR with respect to the caustic network, and not only on their different effective sizes. In the other quasars, the EW model is preferred. For all objects, the PW model has a lower probability. We conclude that disk geometries with kinematics dominated by either Keplerian rotation or equatorial outflow best reproduce the microlensing effects on the MgII and H$α$ emission lines. The half-light radii of the MgII and H$α$ BLRs are measured in the range of 3 to 25 light-days. The size of the region emitting the low-ionization lines is larger than the region emitting the high-ionization lines, with a factor of four measured between the sizes of the MgII and CIV emitting regions. The microlensing radii of the BLRs are found to be systematically below the radius-luminosity ($R -L$) relations derived from reverberation mapping, confirming that the intrinsic dispersion of the BLR radii with respect to the $R-L$ relations is large, but also revealing a selection bias that affects microlensing-based BLR size measurements.

astro-ph.GA↗

arXiv2024

Size and kinematics of the CIV broad emission line region from microlensing-induced line profile distortions in two gravitationally lensed quasars

We analyzed the CIV line profile distortions due to microlensing in two quasars, J1339 and J1138. J1339 shows a strong, asymmetric line profile deformation, while J1138 shows a more modest, symmetric deformation. To probe the CIV broad line region (BLR), we compared the observed line profile deformations to simulated ones. The simulations are based on three simple BLR models, a Keplerian disk (KD), an equatorial wind (EW), and a polar wind (PW), of various sizes, inclinations, and emissivities. We find that the line profile deformations can be reproduced with the simple BLR models under consideration, with no need for more complex geometries or kinematics. The models with disk geometries (KD and EW) are preferred, while the PW model is definitely less likely. For J1339, we find the CIV BLR half-light radii to be $r_{1/2} =$ 5.1 $^{+4.6}_{-2.9}$ light-days and $r_{1/2} =$ 6.7 $^{+6.0}_{-3.8}$ light-days from spectra obtained in 2014 and 2017, respectively. They do agree within uncertainties. For J1138, the amplitude of microlensing is smaller and more dependent on the macro-magnification factor. From spectra obtained in 2005 (single epoch), we find $r_{1/2} =$ 4.9 $^{+4.9}_{-2.7}$ light-days and $r_{1/2}= $ 12 $^{+13}_{-8}$ light-days for two extreme values of the macro-magnification factor. Combining these new measurements with those previously obtained for the quasars Q2237$+$0305 and J1004$+$4112, we show that the BLR radii estimated from microlensing do follow the CIV radius--luminosity relation obtained from reverberation mapping, although the microlensing radii seem to be systematically smaller, which could indicate either a selection bias or a real offset (abridged).

astro-ph.GA↗

arXiv2023

Microlensing of the broad emission line region in the lensed quasar J1004+4112

J1004+4112 is a lensed quasar for which the first broad emission line profile deformations due to microlensing were identified. Detailed interpretations of these features have nevertheless remained controversial. Based on 15 spectra obtained from 2003 to 2018, we revisit the microlensing effect that distorts the CIV broad emission line profile. We show that the microlensing-induced line profile distortions in image A, although variable, are remarkably similar over a period of 15 years. They are characterized by a strong magnification of the blue part of the line profile, a strong demagnification of the red part of the line profile, and a small-to-negligible demagnification of the line core. We used the microlensing effect to constrain the broad emission-line region (BLR) size, geometry, and kinematics. For this purpose, we modeled the deformation of the emission lines considering three simple, representative BLR models: a Keplerian disk, an equatorial wind, and a biconical polar wind, with various inclinations with respect to the line of sight. We find that the observed magnification profile of the CIV emission line can be reproduced with the simple BLR models we considered, without the need for more complex BLR features. The magnification appears dominated by the position of the BLR with respect to the caustic network -- and not by the velocity-dependent size of the BLR. The favored models for the CIV BLR are either the Keplerian disk or the equatorial wind, depending on the orientation of the BLR axis with respect to the caustic network. We also find that the polar wind model can be discarded. We measured the CIV BLR half-light radius as $r_{1/2} = 2.8^{+2.0}_{-1.7}$ light-days. This value is smaller than the BLR radius expected from the radius-luminosity relation derived from reverberation mapping, but it is still in reasonable agreement given the large uncertainties.

astro-ph.GA↗

arXiv2022

Dissecting the active galactic nucleus in Circinus -- III. VLT/FORS2 polarimetry confirms dusty cone illuminated by a tilted accretion disc

We present polarimetric maps of the Circinus galaxy nucleus in the $BVRI$ bands, obtained with VLT/FORS2. Circinus is the closest Seyfert 2 galaxy and harbours an archetypal obscured active galactic nucleus (AGN). Recent high angular resolution imaging revealed that a major fraction of its mid-infrared (MIR) emission is coming from the polar region. Previously, we demonstrated that these observations are consistent with a model of a compact dusty disc and a hyperboloid shell, resembling a hollow cone on larger scales. Here we focus on the AGN core, up to 40 pc from the central engine, and compare the observations to the radiative transfer models. Polarization maps reveal a conical structure, coinciding with the ionization cone. The wavelength-dependence of the polarization degree indicates that scattering on dust grains is producing polarization. The observed polarization degree ($\approx1-3\%$) is lower than predicted by the models; however, this is only a lower limit, since stellar emission dominates the total flux in the optical. The observed polarization angle ($\approx30$ degrees) is reproduced by the model of a dusty disc with a hollow cone that is illuminated by a tilted anisotropic central source. An accretion disc aligned with the ionization cone axis, and alternative dust geometries, such as a paraboloid shell, or a torus enveloped by ambient dust, are inconsistent with the data. We conclude that the optical polarimetric imaging supports earlier evidence for the presence of dust in the polar region, tentatively associated with dusty outflows.

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arXiv2021

The first supermassive black hole mass measurement in active galactic nuclei using the polarization of broad emission line Mg II

Spectropolarimetric efforts in the last few years have provided an efficient method that is based on the profiles of the polarization plane position angle of broad emission lines in active galactic nuclei (AGNs). Here we present black hole measurements of SBS 1419+538 using spectropolarimetric observations in the Mg II spectral band. The observations are performed by 6m telescope of SAO RAS using SCORPIO-2. We found a good agreement for the estimated supermassive black hole (SMBH) mass for this object using spectropolarimetry when compared with the mass obtained using other methods.

astro-ph.GA↗

arXiv2021

Linear Spectropolarimetric Analysis of Fairall 9 with VLT/FORS2

The quasar Main Sequence (MS) appears to be an incredibly powerful tool to organize the diversity in large samples of type-1 quasars but the most important physical parameters governing it are still unclear. Here we investigate the origin of the broadening and of a defining feature of Population B sources: a strong redward asymmetry of the Balmer emission lines. We focus on a prototypical source, Fairall 9. Spectropolarimetric data of the Fairall 9 broad H$β$ and H$α$ profiles allowed for a view of the geometric and dynamical complexity of the line emitting regions. Measurements (1) provided evidence of rotational motion; (2) were helpful to test the presence of polar and equatorial scatterers, and their association with non-virial motions.

astro-ph.GA↗

arXiv2020

Estimating supermassive black hole masses in AGNs using polarization of broad MgII, H$α$ and H$β$ lines

For type-1 active galactic nuclei (AGNs) for which the equatorial scattering is the dominant broad line polarization mechanism, it is possible to measure the supermassive black hole mass by tracing the Keplerian motion across the polarization plane positionangle. So far this method has been used for 30 objects but only for H$α$ emission line. We explore the possibilities this method for determining SMBH masses using polarization in broad emission lines by applying it for the first time to Mg II$λ$2798AA spectral line. We use 3D Monte Carlo radiative transfer code stokes for simultaneous modeling of equatorial scattering of H$α$, H$β$ and Mg II lines. We included vertical inflows and outflows in the MgII broad line region (BLR). We find that polarization states of H$α$ and H$β$ lines are almost identical and SMBH mass estimates differ by 7%. For Mg II line, we find that polarization angle $φ$ exhibits an additional "plateau" with a constant $φ$, which deviates than the profiles expected for pure Keplerian motion. SMBH mass estimates using Mg II line are higher by up to 35% than those obtained from H$α$ and H$β$ lines. Our model shows that for vertical inflows and outflows in the BLR that is higher or comparable to Keplerian velocity, this method can be applied as a first approximation for obtaining SMBH mass.

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arXiv2019

Comparison between the influence of outflows and supermassive binary black holes in active galactic nuclei on the polarization angle profiles

Optical polarization signal coming from the innermost part of active galactic nuclei (AGNs) is highly sensitive on the geometry and kinematics of the central engine. Due to the compact size of the AGN central region, which is spatially unresolved with current observing facilities, we rely on spectropolarimetry which can provide us insight in their hidden physics. We model equatorial scattering for various broad line region (BLR) configurations using radiative transfer code STOKES. We analyze the polarization position angle () profiles for four supermassive binary black holes (SMBBHs) models and compare them with the profiles found for a unified model in AGNs with a single supermassive black hole (SMBH) and with notable outflowing velocity component of the BLR.. We find that the profiles for SMBBHs are axis-symmetric, while the profiles for a single SMBHs are point-symmetric and that there is a clear distinction between the two cases. Our conclussion is that spectropolarimetry might play a key role in the search for the SMBBHs by inspecting the polarization angle profiles.

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