Autorzy: Khadka, Narayan ; Yu, Zhefu ; Zajaček, Michal ; Martinez-Aldama, Mary Loli ; Czerny, Bożena ; Ratra, Bharat

Czasopismo: Monthly Notices of the Royal Astronomical Society, 2021, 508, pp.4722

We use 78 reverberation-measured Mg II time-lag quasars (QSOs) in the redshift range 0.0033 ≤ z ≤ 1.89 to constrain cosmological parameters in six different cosmological models. The basis of our method is the use of the radius-luminosity or R-L relation to standardize these 78 Mg II QSOs. In each cosmological model, we simultaneously determine R-L relation and cosmological model parameters, thus avoiding the circularity problem. We find that the R-L relation parameter values are independent of the cosmological model used in the analysis, thus, establishing that current Mg II QSOs are standardizable candles. Cosmological constraints obtained using these QSOs are significantly weaker than, but consistent with, those obtained from a joint analysis of baryon acoustic oscillation (BAO) observations and Hubble parameter [H(z)] measurements. So, we also analyse these QSOs in conjunction with the BAO + H(z) data and find cosmological constraints consistent with the standard spatially flat ΛCDM model as well as with mild dark energy dynamics and a little spatial curvature. A larger sample of higher quality reverberation-measured QSOs should have a smaller intrinsic dispersion and so should provide tighter constraints on cosmological parameters.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021MNRAS.508.4722K/abstract

Autorzy: Prince, Raj; Raman, Gayathri ; Khatoon, Rukaiya ; Agarwal, Aditi ; Varun ; Gupta, Nayantara ; Czerny, Bożena ; Majumdar, Pratik

Czasopismo: Monthly Notices of the Royal Astronomical Society, 2021, 508, pp.315

OJ 287 is a well-studied binary black hole (BBH) system, which occasionally exhibits bright X-ray and optical flares. Here we present a detailed spectral study of its second brightest X-ray flare observed during 2019-2020 using archival Swift and Nuclear Spectroscopic Telescope Array (NuSTAR) observations along with Target of Opportunity observations from AstroSat. The entire flaring period is divided into three states, defined as low, intermediate and high states. The variation of the hardness ratio with 0.3-10.0 keV integrated flux suggests a 'softer-when-brighter' behaviour, as also previously reported based on flux-index variations. Simultaneous high-state X-ray spectra obtained using Swift, NuSTAR and AstroSat are very steep with a power-law index >2. A significant spectral change is observed in the spectrum obtained with the Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) onboard AstroSat, which is consistent with the spectrum from NuSTARand from the X-ray Telescope (XRT) onboard Swift. Together, optical-ultraviolet and X-ray spectra during the high-flux state suggest the emergence of a new high BL Lacertae component. We have modelled the synchrotron peak with the publicly available code called GAMERA for low-, intermediate- and high-flux states. Our modelling suggests the need for a high magnetic field to explain the high state under leptonic scenarios. An increase in the magnetic field value inside the jet could be linked to an increase in the accretion rate, as expected in the BH-disc impact scenario. The colour-magnitude diagram reveals a 'bluer-when-brighter' spectral energy distribution chromatism during the flaring period. Different chromatism or no chromatism on various occasions suggests a complex origin of optical emission, which is believed to be produced by disc impact or through synchrotron emission in the jet.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021MNRAS.508..315P/abstract

Autorzy: Jiang, Bo-Wei; ....., Czerny, Bożena; ...

Czasopismo: Monthly Notices of the Royal Astronomical Society, 2021, 508, pp.79

The quasar main sequence 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. However, we suggest that the polarization properties appear to be more consistent with a warped disc geometry induced by Lense-Thirring precession.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021MNRAS.508...79J/abstract

Autorzy: Naddaf, Mohammad-Hassan; Czerny, Bożena; Szczerba, Ryszard

Czasopismo: The Astrophysical Journal, 2021, 920, id.30

The dynamics of the broad line region (BLR) in active galaxies is an open question; direct observational constraints suggest a predominantly Keplerian motion, with possible traces of inflow or outflow. In this paper we study in detail the physically motivated BLR model of Czerny & Hryniewicz based on the radiation pressure acting on dust at the surface layers of the accretion disk (AD). We consider here a nonhydrodynamical approach to the dynamics of the dusty cloud under the influence of radiation coming from the entire AD. We use here a realistic description of the dust opacity, and we introduce two simple geometrical models of the local shielding of the dusty cloud. We show that the radiation pressure acting on dusty clouds is strong enough to lead to dynamical outflow from the AD surface, so the BLR has a dynamical character of a (mostly failed) outflow. The dynamics strongly depends on the Eddington ratio of the source. Large Eddington ratio sources show a complex velocity field and large vertical velocities with respect to the AD surface, while for lower Eddington ratio sources vertical velocities are small and most of the emission originates close to the AD surface. Cloud dynamics thus determines the 3D geometry of the BLR.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021ApJ...920...30N/abstract

Autorzy: Prince, Raj ; Agarwal, Aditi ; Gupta, Nayantara ; Majumdar, Pratik ; Czerny, Bożena ; Cellone, Sergio A. ; Andruchow, I.

Czasopismo: Astronomy & Astrophysics, 2021, 654, id.A38

Context. The blazar OJ 287 has been proposed as binary black hole system based on its periodic optical outburst. Black hole binary systems are scarce among blazars with parsec scale jets, and hence this source is exciting to study Aims: The BL Lac OJ 287 is an interesting object for multiwavelength study due to its periodic outbursts. We analysed the optical, X-ray and γ-ray data of OJ 287 for the period of 2017-2020. There are several high states in optical-UV and X-ray frequencies during this period. Based on the observed variability in optical and X-ray frequencies, the entire period 2017-2020 is divided in five segments, in this paper referred as A, B, C, D, and E. A detailed temporal and spectral analysis is performed to understand the nature of the flaring activities of OJ 287. Methods: To understand the temporal variability in this source we studied the intraday and fractional variability for all the various states. In additon, fast variability time was also estimated in order to understand the nature of variability. Furthermore, the multiwavelength spectral energy distribution (SED) modeling was performed to know more about the physical processes responsible for the simultaneous broadband emission and the fast variability. Results: The Fermi-LAT observations show a moderate flux level of this source in γ-ray frequency throughout this period, though flux variability has been observed. The source has shown a strong flux variability in X-ray, optical, and UV during early 2017 and mid 2020 when the source was in very high state. A single-zone synchrotron self-Compton emission model is considered to model the SED, and this helps us to explore the nature of this BL Lac with binary supermassive black holes.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021%26A...654A..38P/abstract

Autorzy: Martínez-Aldama, Mary Loli; Panda, Swayamtrupta; Czerny, Bożena; Marinello, Murilo; Marziani, Paola; Dultzin, Deborah

Czasopismo: The Astrophysical Journal, 2021, 918, id.29

In this second paper in the series, we carefully analyze the observational properties of the optical Fe II and near-IR Ca II triplet in active galactic nuclei (AGNs), as well as the luminosity, black hole mass, and Eddington ratio in order to define the driving mechanism behind the properties of our sample. The Ca II shows an inverse Baldwin effect, bringing out the particular behavior of this ion with respect to the other low-ionization lines such as Hβ. We performed a principal component analysis, where 81.2% of the variance can be explained by the first three principal components drawn from the FWHMs, luminosity, and equivalent widths. The first principal component (PC1) is primarily driven by the combination of black hole mass and luminosity with a significance over 99.9%, which in turn is reflected in the strong correlation of the PC1 with the Eddington ratio. The observational correlations are better represented by the Eddington ratio; thus, it could be the primary mechanism behind the strong correlations observed in the Ca II-Fe II sample. Since calcium belongs to the α-elements, the Fe II/Ca II flux ratio can be used as a chemical clock for determining the metal content in AGNs and trace the evolution of the host galaxies. We confirm the de-enhancement of the ratio Fe II/Ca II by the Eddington ratio, suggesting a metal enrichment of the BLR in intermediate-z with respect to low-z objects. A larger sample, particularly at z > 2, is needed to confirm the present results.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021ApJ...918...29M/abstract

Autorzy: Zajaček, Michal et al.

Czasopismo: The Astrophysical Journal, 2021, 912, id.10

Using six years of spectroscopic monitoring of the luminous quasar HE 0435-4312 (z = 1.2231) with the Southern African Large Telescope, in combination with photometric data (CATALINA, OGLE, SALTICAM, and BMT), we determined a rest-frame time delay of 296+13−14 days between the Mg II broad-line emission and the ionizing continuum using seven different time-delay inference methods. Time-delay artifact peaks and aliases were mitigated using the bootstrap method and prior weighting probability function, as well as by analyzing unevenly sampled mock light curves. The Mg II emission is considerably variable with a fractional variability of ∼5.4%, which is comparable to the continuum variability (∼4.8%). Because of its high luminosity (L3000 = 1046.4 erg s-1), the source is beneficial for a further reduction of the scatter along the Mg II-based radius-luminosity relation and its extended versions, especially when the highly accreting subsample that has an rms scatter of ∼0.2 dex is considered. This opens up the possibility of using the high-accretor Mg II-based radius-luminosity relation for constraining cosmological parameters. With the current sample of 27 reverberation-mapped sources, the best-fit cosmological parameters (Ωm, ΩΛ) = (0.19; 0.62) are consistent with the standard cosmological model within the 1σ confidence level.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021ApJ...912...10Z/abstract

Autorzy: Śniegowska, Marzena; Marziani, Paola; Czerny, Bożena; Panda, Swayamtrupta; Martínez-Aldama, Mary Loli; del Olmo, Ascensión; D'Onofrio, Mauro

Czasopismo: The Astrophysical Journal, 2021, 910, id.115

We present an analysis of UV spectra of 13 quasars believed to belong to extreme Population A (xA) quasars, aimed at the estimation of the chemical abundances of the broad-line-emitting gas. Metallicity estimates for the broad-line-emitting gas of quasars are subject to a number of caveats; xA sources with the strongest Fe II emission offer several advantages with respect to the quasar general population, as their optical and UV emission lines can be interpreted as the sum of a low-ionization component roughly at quasar rest frame (from virialized gas), plus a blueshifted excess (a disk wind), in different physical conditions. Capitalizing on these results, we analyze the component at rest frame and the blueshifted one, exploiting the dependence of several intensity line ratios on metallicity Z. We find that the validity of intensity line ratios as metallicity indicators depends on the physical conditions. We apply the measured diagnostic ratios to estimate the physical properties of sources such as density, ionization, and metallicity of the gas. Our results confirm that the two regions (the low-ionization component and the blueshifted excess) of different dynamical conditions also show different physical conditions and suggest metallicity values that are high, and probably the highest along the quasar main sequence, with Z ∼ 20-50 Z⊙, if the solar abundance ratios can be assumed constant. We found some evidence of an overabundance of aluminum with respect to carbon, possibly due to selective enrichment of the broad-line-emitting gas by supernova ejecta.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021ApJ...910..115S/abstract

Autorzy: Czerny, B. ; Martínez-Aldama, M. L. ; Wojtkowska, G. ; Zajaček, M. ; Marziani, P. ; Dultzin, D. ; Naddaf, M. H.; Panda, S. ; Prince, R. ; Przyluski, R. ; Ralowski, M. ; Śniegowska, M.

Czasopismo: Acta Physica Polonica A, 2021, 139, 389

Recent measurements of the parameters of the Concordance Cosmology Model (ΛCDM) done in the low-redshift Universe with Supernovae Ia/Cepheids, and in the distant Universe done with Cosmic Microwave Background (CMB) imply different values for the Hubble constant (67.4 ± 0.5 km/s/Mpc from Planck vs 74.03 ± 1.42 km/s/Mpc, Riess et al. 2019). This Hubble constant tension implies that either the systematic errors are underestimated, or the ΛCDM does not represent well the observed expansion of the Universe. Since quasars - active galactic nuclei - can be observed in the nearby Universe up to redshift z ∼ 7.5, they are suitable to estimate the cosmological properties in a large redshift range. Our group develops two methods based on the observations of quasars in the late Universe up to redshift z∼4.5, with the objective to determine the expansion rate of the Universe. These methods do not yet provide an independent measurement of the Hubble constant since they do not have firm absolute calibration but they allow to test the ΛCDM model, and so far no departures from this model were found.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021AcPPA.139..389C/abstract

Autorzy: Prince, Raj; Czerny, Bożena; Pollo, Agnieszka

Czasopismo: The Astrophysical Journal, 2021, 909, id.58

The symmetry axes of active galactic nuclei (AGNs) are randomly distributed in space, but highly inclined sources are heavily obscured and are not seen as quasars with broad emission lines. The obscuring torus geometry determines the average viewing angle, and if the torus geometry changes with the redshift, this average viewing angle will also change. Thus, the ratio between the isotropic luminosity and observed luminosity may change systematically with redshift. Therefore, if we use quasars to measure the luminosity distance by evaluating the isotropic absolute luminosity and measuring the observed flux, we can have a redshift-dependent bias that can propagate to cosmological parameters. We propose a toy model for testing the effect of viewing angle uncertainty on the measurement of the luminosity distance. The model is based on analytical description of the obscuring torus applied to one-parameter observational data. It illustrates the possible change of the torus covering factor between the two chosen redshift ranges. We have estimated the possible errors in specific cosmological parameters (H0, Ωm) for the flat Lambda cold dark matter cosmology if a method is calibrated at low redshift and applied to the higher redshift. The errors in the cosmological parameters due to potential dependence of the viewing angle on redshift are found to be potentially significant, and the effect will have to be accommodated in the future in all quasar-based cosmological methods. A careful systematic study of AGNs means that a viewing angle across the redshift is necessary, with the use of appropriate samples and models that uniquely determine the inclination of each source.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021ApJ...909...58P/abstract

Autorzy: You, Bei;...., Czerny, B., .....

Czasopismo: Nature Communications, 2021, 12, 1025

A black hole X-ray binary produces hard X-ray radiation from its corona and disk when the accreting matter heats up. During an outburst, the disk and corona co-evolves with each other. However, such an evolution is still unclear in both its geometry and dynamics. Here we report the unusual decrease of the reflection fraction in MAXI J1820+070, which is the ratio of the coronal intensity illuminating the disk to the coronal intensity reaching the observer, as the corona is observed to contrast during the decay phase. We postulate a jet-like corona model, in which the corona can be understood as a standing shock where the material flowing through. In this dynamical scenario, the decrease of the reflection fraction is a signature of the corona's bulk velocity. Our findings suggest that as the corona is observed to get closer to the black hole, the coronal material might be outflowing faster.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021NatCo..12.1025Y/abstract

Autorzy: Wildy, Conor; Landt, Hermine; Ward, Martin J.; Czerny, Bożena; Kynoch, Daniel

Czasopismo: Monthly Notices of the Royal Astronomical Society, 2021, 500, 2063

The nucleus of the active galaxy NGC 5548 was the target of two intensive spectroscopic monitoring campaigns at X-ray, ultraviolet (UV), and optical frequencies in 2013/2014. These campaigns detected the presence of a massive obscuration event. In 2016/2017, Landt et al. conducted a near-IR spectroscopic monitoring campaign on NGC 5548 and discovered He I 1.08-μm absorption. Here, we decompose this absorption into its components and study its time variability. We attribute the narrow He I absorption lines to the warm absorber (WA) and, as for the newly appeared low-ionization WA lines in the UV, their presence is most likely due to a reduction in ionization parameter caused by the obscurer. The observed variability of the narrow He I absorption is consistent with what is expected for the WA. Most importantly, we also detect fast, broad He I absorption, which we attribute to the obscurer. This He I broad absorption, which is indicative of a high column density gas, is unsaturated and variable on time-scales of a few months. The observed variability of the obscurer is mainly due to changes in ionization, although density changes also play a role. We test the physical cycle model of Dehghanian et al. which proposes that helium recombination can account for how the obscurer influences the physics of the WA gas. Our results support their model, but also indicate that the reality might be more complex.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021MNRAS.500.2063W/abstract

Autorzy: Borkar, A.; Adhikari, T. P.; Różańska, A.; Markowitz, A. G.; Boorman, P.; Czerny, B.; Migliori, G.; De Marco, B.; Karas, V.

Czasopismo: Monthly Notices of the Royal Astronomical Society, 2021, 500, 3556

We study the multiphase medium in the vicinity of the active galactic nucleus Centaurus A (Cen A). Combined high-resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and Chandra X-ray Observatory indicate that the hot X-ray emitting plasma coexists with the warm and cold media in Cen A. This complex environment is a source of CO lines with great impact for its diagnostics. We present the images from the two above-mentioned instruments covering the nuclear region (diameter of 10 arcsec, i.e. ∼180 pc), and we study the conditions for plasma thermal equilibrium and possible coexistence of cool clouds embedded within the hot X-ray emitting gas. Further, we demonstrate that the multiphase medium originates naturally by the thermal instability arising due to the interaction of the high-energy radiation field from the nucleus with the ambient gas and dust. We demonstrate that cold gas clouds can coexist in the mutual contact with hot plasma, but even colder dusty molecular clouds have to be distanced by several hundred pc from the hot region. Finally, we propose a 3D model of the appearance of the hot plasma and the CO line-emitting regions consistent with the Chandra image, and we derive the integrated emissivity in specific molecular lines observed by ALMA from this model. To reproduce the observed images and the CO line luminosity the dusty shell has to be ∼420 pc thick and located at ∼1000 pc from the centre.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2021MNRAS.500.3536B/abstract

Autorzy: Hosseini, S. Elaheh; Zajaček, Michal; Eckart, Andreas; Sabha, Nadeen B.; Labadie, Lucas

Czasopismo: Astronomy & Astrophysics, 2020, 644, A105

Context. The density of the ambient medium around a supermassive black hole (SMBH) and the way it varies with distance plays an important role in our understanding of the inflow-outflow mechanisms in the Galactic centre (GC). This dependence is often fitted by spherical power-law profiles based on observations in the X-ray, infrared (IR), submillimetre (submm), and radio domains. Aims: Nevertheless, the density profile is poorly constrained at the intermediate scales of 1000 Schwarzschild radii (Rs). Here we independently constrain the spherical density profile using the stellar bow shock of the star S2 which orbits the SMBH at the GC with the pericentre distance of 14.4 mas (∼1500 Rs). Methods: Assuming an elliptical orbit, we apply celestial mechanics and the theory of bow shocks that are at ram pressure equilibrium. We analyse the measured IR flux density and magnitudes of S2 in the L'-band (3.8 micron) obtained over seven epochs in the years between 2004-2018. We put an upper limit on the emission from S2's associated putative bow shock and constrain the density profile of the ambient medium. Results: We detect no significant change in S2 flux density until the recent periapse in May 2018. The intrinsic flux variability of S2 is at the level of 2-3%. Based on the dust-extinction model, the upper limit on the number density at the S2 periapse is ∼1.87 × 109 cm-3, which yields a density slope of at most 3.20. Using the synchrotron bow-shock emission, we obtain the ambient density of ≲1.01 × 105 cm-3 and a slope of ≲1.47. These values are consistent with a wide variety of media from hot accretion flows to potentially colder and denser media comparable in properties to broad-line-region clouds. However, a standard thin disc can be excluded at the distance of S2's pericentre. Conclusions: With the current photometry sensitivity of 0.01 mag, we are not able to make stringent constraints on the density of the ambient medium in the GC using S2-star observations. We can distinguish between hot accretion flows and thin, cold discs, where the latter can be excluded at the scale of the S2 periapse. Future observations of stars in the S cluster using instruments such as Mid-IR Extremely Large Telescope Imager and Spectrograph at Extremely Large Telescope with the photometric sensitivity of as much as 10-3 mag will allow the GC medium to be probed at intermediate scales at densities as low as ∼700 cm-3 in case of non-thermal bow-shock emission. The new instrumentation, in combination with discoveries of stars with smaller pericentre distances, will help to independently constrain the density profile around Sagittarius A* (Sgr A*).

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020A%26A...644A.105H/abstract

Autorzy: Peißker, Florian; Eckart, Andreas; Zajaček, Michal; Ali, Basel; Parsa, Marzieh

Czasopismo: Astrophysical Journal, 2020, 899, 50

We present high-pass filtered NACO and SINFONI images of the newly discovered stars S4711-S4715 between 2004 and 2016. Our deep H+K-band (SINFONI) and K-band (NACO) data show the S-cluster star S4711 on a highly eccentric trajectory around Sgr A* with an orbital period of 7.6 yr and a periapse distance of 144 au to the supermassive black hole (SMBH). S4711 is hereby the star with the shortest orbital period and the smallest mean distance to the SMBH during its orbit to date. The used high-pass filtered images are based on coadded data sets to improve the signal to noise. The spectroscopic SINFONI data let us determine detailed stellar properties of S4711 like the mass and the rotational velocity. The faint S-cluster star candidates, S4712-S4715, can be observed in a projected distance to Sgr A* of at least temporarily ≤120 mas. From these stars, S4714 is the most prominent, with an orbital period of 12 yr and an eccentricity of 0.985. The stars S4712-S4715 show similar properties, with magnitudes and stellar masses comparable to those of S4711. The MCMC simulations determine confidently precise uncertainties for the orbital elements of S62 and S4711-S4715. The presence of S4711 in addition to S55, S62, and the also newly found star S4714 implies a population of faint stars that can be found at distances to Sgr A* that are comparable to the size of our solar system. These short orbital time period stars in the dense cluster around the SMBH in the center of our Galaxy are perfect candidates to observe gravitational effects such as the periapse shift.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...899...50P/abstract

Autorzy: Zajaček, Michal; Czerny, Bożena; Martinez-Aldama, Mary Loli; Rałowski, Mateusz; Olejak, Aleksandra; Panda, Swayamtrupta; Hryniewicz, Krzysztof; Śniegowska, Marzena; Naddaf, Mohammad-Hassan; Pych, Wojtek; Pietrzyński, Grzegorz; Sobrino Figaredo, C.; Haas, Martin; Średzińska, Justyna; Krupa, Magdalena; Kurcz, Agnieszka; Udalski, Andrzej; Gorski, Marek; Sarna, Marek

Czasopismo: Astrophysical Journal, 2019, 870, 84

We present the monitoring of the active galactic nuclei continuum and Mg II broad-line emission for the quasar HE 0413-4031 (z = 1.38) based on the six-year monitoring by the South African Large Telescope (SALT). We manage to estimate a time-delay of 302.6+28.7−33.1 days in the rest frame of the source using seven different methods: interpolated cross-correlation function, discrete correlation function (DCF), z-transformed DCF, JAVELIN, two estimators of data regularity (Von Neumann, Bartels), and χ2 method. This time-delay is below the value expected from the standard radius-luminosity relation. However, based on the monochromatic luminosity of the source and the spectral energy distribution modeling, we interpret this departure as the shortening of the time-delay due to the higher accretion rate of the source, with the inferred Eddington ratio of ∼0.4. The Mg II line luminosity of HE 0413-4031 responds to the continuum variability as Lline∝L0.43±0.10cont , which is consistent with the light-travel distance of the location of Mg II emission at Rout ∼ 1018 cm. Using the data of 10 other quasars, we confirm the radius-luminosity relation for the broad Mg II line, which was previously determined for the broad Hβ line for lower-redshift sources. In addition, we detect a general departure of higher-accreting quasars from this relation in analogy to the Hβ sample. After the accretion-rate correction of the light-travel distance, the Mg II-based radius-luminosity relation has a small scatter of only 0.10 dex.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...896..146Z/abstract

Autorzy: Tursunov, Arman; Zajaček, Michal; Eckart, Andreas; Kološ, Martin; Britzen, Silke; Stuchlík, Zdeněk; Czerny, Bozena; Karas, Vladimír

Czasopismo: Astrophysical Journal, 2020, 897, 99

Recently, near-infrared GRAVITY@ESO observations at 2.2 μm announced the detection of three bright "flares" in the vicinity of the Galactic center supermassive black hole (SMBH) that exhibited orbital motion at a distance of about 6-11 gravitational radii from an ∼4 × 106 M☉ black hole. There are indications of the presence of a large-scale, organized component of the magnetic field at the Galactic center. Electromagnetic effects on the flare dynamics were previously not taken into account despite the relativistic motion of a plasma in magnetic field leading to the charge separation and nonnegligible net charge density in the plasma. Applying various approaches, we find the net charge number density of the flare components of the order of 10-3-10-4 cm-3, while the particles' total number density is of the order of 106-108 cm-3. However, even such a tiny excess of charged particles in the quasi-neutral plasma can significantly affect the dynamics of flare components, which can then lead to the degeneracy in the measurements of spin of the SMBH. Analyzing the dynamics of recent flares in the case of the rapidly rotating black hole, we also constrain the inclination angle between the magnetic field and spin axis to α < 50°, as for larger angles, the motion of the hot spot is strongly chaotic.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...897...99T/abstract

Autorzy: Śniegowska, Marzena; Kozłowski, Szymon; Czerny, Bożena; Panda, Swayamtrupta; Hryniewicz, Krzysztof

Czasopismo: Astrophysical Journal, 2020, 900, 64

Active galaxies form a clear pattern in the optical plane showing the correlation between the FWHM of the Hβ line and the ratio of the equivalent width (EW) of the optical Fe II emission and the broad EW(Hβ). This pattern is frequently referred to as the quasar main sequence. In this paper, we study the UV plane showing the FWHM of Mg II line against the ratio of the EW of UV Fe II emission to the broad EW(Mg II). We show that the UV plane trends are different, with the underlying strong correlation between the FWHM(Mg II) and the EW(Mg II). This correlation is entirely driven by the choice of the continuum used to measure the EW(Mg II). If instead of the observationally determined continuum, we use a theoretically motivated power law extrapolated from the wide wavelength range, the behavior of the FWHM versus EW for Mg II becomes similar to the behavior for Hβ. Such a similarity is expected since both the lines belong to the low-ionization group of emission lines and come from a similar region. We discuss the behavior of the lines in the context of the broad line region model based on the presence of dust in the accretion disk atmosphere.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...900...64S/abstract

Autorzy: Ali, Basel; Paul, Daria; Eckart, Andreas; Parsa, Marzieh; Zajacek, Michal; Peißker, Florian; Subroweit, Matthias; Valencia-S., Monica; Thomkins, Lauritz; Witzel, Gunther

Czasopismo: Astrophysical Journal, 2020, 896, 100

We present a detailed analysis of the kinematics of 112 stars that mostly comprise the high-velocity S cluster and orbit the supermassive black hole Sgr A* at the center of the Milky Way. For 39 of them, orbital elements are known; for the remainder, we know proper motions. The distribution of the inclinations and the proper motion flight directions deviate significantly from a uniform distribution, which one expects if the orientation of the orbits are random. Across the central arcseconds, the S-cluster stars are arranged in two almost edge-on disks that are located at a position angle approximately ±45° with respect to the Galactic plane. The angular momentum vectors for stars in each disk point in both directions, I.e., the stars in a given disk rotate in opposite ways. The poles of this structure are located only about 25° from the line of sight. This structure may be the result of a resonance process that started with the formation of the young B-dwarf stars in the cluster about 6 Myr ago. Alternatively, it indicated the presence of a disturber at a distance from the center comparable to the distance of the compact stellar association IRS 13.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...896..100A/abstract

Autorzy: Marziani, P.; Bon, E.; Bon, N.; Martinez-Aldama, M. L.; Stirpe, G. M.; D'Onofrio, M.; del Olmo, A.; Negrete, C. A.; Dultzin, D.

Czasopismo: Contributions of the Astronomical Observatory Skalnaté Pleso, 2020, 50, 244

Quasars accreting matter at very high rates (known as extreme Population A [xA]) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. We report on the developments of a method that is based on ``virial luminosity'' estimates from measurements of emission line widths of xA quasars. The approach is conceptually equivalent to the virial estimates based on early and late type galaxies. The main issues related to the cosmological application of luminosity estimates from xA quasar line widths are the identification of proper emission lines whose broadening is predominantly virial over a wide range of luminosity, and the assessment of the effect of the emitting region orientation with respect to the line of sight. We report on recent developments concerning the use of the AlIIIλ 1860 intermediate ionisation line and of the Hydrogen Balmer line Hβ as ``virial broadening estimators.''

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020CoSka..50..244M/abstract

Autorzy: Bon, N.; Marziani, P.; Bon, E.; Negrete, C. A.; Dultzin, D.; del Olmo, A.; D'Onofrio, M.; Martínez-Aldama, M. L.

Czasopismo: Astronomy & Astrophysics, 2020, 635, A151

Context. The quasar class of extreme Population A (xA) (also known as super-Eddington accreting massive black holes, SEAMBHs) has been hailed as potential distance indicators for cosmology. Aims: The aim of this paper is to define tight criteria for their proper identification, starting from the main selection criterion RFeII > 1, and to identify potential intruders that do not meet the selection criteria, which nonetheless have been selected as xA because of the coarseness of automatic searches. The inclusion of the spurious xA sources may dramatically increase the dispersion in the Hubble diagram of quasars, which were obtained from virial luminosity estimates. Methods: We studied a sample of 32 low-z quasars that were originally selected from the seventh data release of the Sloan Digital Sky Survey as xA or SEAMBHs, which have been proved to be almost certainly misclassified sources. All of them show moderate to strong Fe II emission and the large majority show strong absorption features in their spectra which are typical of fairly evolved stellar populations. We performed a simultaneous fit of a host galaxy spectrum, active galactic nucleus (AGN) continuum, FeII template, and emission lines to spectra, using the fitting technique based on ULySS, the full spectrum fitting package. We derived the main accretion parameters (i.e., luminosity, black hole mass, and Eddington ratio) and investigate the relation between host galaxy properties and AGN. Results: For sources in our sample with spectral types that correspond to a relatively low Eddington ratio, we find an overall consistency between HβNC, [O III]λλ4959,5007 line shifts, and the mean stellar velocity obtained from the host galaxy fit (within ≲|60| km s-1). Only one source in our sample qualifies as a xA source. Conclusions: The correct classification of spectra that were contaminated by heavy absorption requires careful determination of the host galaxy spectrum. Contamination and misclassification are not usual in the identification of the xAs, nor at low z or at high z. We find a high fraction of host galaxy spectrum; in half of the sample this is even higher than 40%. When absorption lines are prominent, and the fraction of the host galaxy is high, host galaxy spectrum mimics FeII, which may result in a mistaken identification of FeII spectral features. We have identified several stellar absorption lines that, along with the continuum shape, may lead to an overestimate of RFeII, and therefore to the misclassification of sources as xA sources.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020A%26A...635A.151B/abstract

Autorzy: Sniegowska, M.; Czerny, B.; Bon, E.; Bon, N.

Czasopismo: Astronomy & Astrophysics, 2020, 641, A167

Context. The changing-look phenomenon observed in a growing number of active galaxies challenges our understanding of the accretion process close to a black hole. Aims: We propose a simple explanation for the sources where multiple semi-periodic outbursts are observed, and the sources are operating close to the Eddington limit. Methods: The outburst are caused by the radiation pressure instability operating in the narrow ring between the standard gas-dominated outer disk and the hot optically thin inner advection-dominated accretion flow. The corresponding limit cycle is responsible for periodic outbursts, and the timescales are much shorter than the standard viscous timescale due to the narrowness of the unstable radial zone. Results: Our toy model gives quantitative predictions and works well for multiple outbursts like those observed in NGC 1566, NGC 4151, NGC 5548, and GSN 069, although the shapes of the outbursts are not yet well modeled, and further development of the model is necessary.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020A%26A...641A.167S/abstract

Autorzy: Zajaček, Michal; Araudo, Anabella; Karas, Vladimír; Czerny, Bożena; Eckart, Andreas

Czasopismo: Astrophysical Journal, 2020, 903, 140

Observations in the near-infrared domain showed the presence of the flat core of bright late-type stars inside ∼0.5 pc from the Galactic center supermassive black hole (Sgr A*), while young massive OB/Wolf-Rayet stars form a cusp. Several dynamical processes were proposed to explain this apparent paradox of the distribution of the Galactic center stellar populations. Given the mounting evidence on the significantly increased activity of Sgr A* during the past million years, we propose a scenario based on the interaction between the late-type giants and a nuclear jet, whose past existence and energetics can be inferred from the presence of γ-ray Fermi bubbles and bipolar radio bubbles. Extended, loose envelopes of red giant stars can be ablated by the jet with kinetic luminosity in the range of Lj ≍ 1041- 1044ergs−1 within the inner ∼0.04 pc of Sgr A* (S-cluster region), which would lead to their infrared luminosity decrease after several thousand jet-star interactions. The ablation of the atmospheres of red giants is complemented by the process of tidal stripping that operates at distances of ≲1 mpc, and by the direct mechanical interaction of stars with a clumpy disk at ≳0.04 pc, which can explain the flat density profile of bright late-type stars inside the inner half parsec from Sgr A*.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...903..140Z/abstract

Autorzy: Martínez-Aldama, Mary Loli; Zajaček, Michal; Czerny, Bożena; Panda, Swayamtrupta

Czasopismo: Astrophysical Journal, 2020, 903, 86

The usage of the radius-luminosity (R-L) relation for the determination of black hole masses across the cosmic history, as well as its application for cosmological studies, motivates us to analyze its scatter, which has recently increased significantly for both the optical (Hβ) and UV (Mg II) lines. To this purpose, we determined the scatter along the R-L relation for an up-to-date reverberation-mapped Mg II sample. Studying linear combinations of the luminosity at 3000 Å with independent parameters such as the FWHM, the UV Fe II strength (RFe II), and the fractional variability (Fvar) for the whole sample, we get only a small decrease in the scatter ( σrms=0.29−0.30 dex). Linear combinations with the dimensionless accretion rate ( M˙ ) and the Eddington ratio lead to significant reductions of the scatter ( σrms∼0.1 dex), albeit both suffering from the interdependency on the observed time delay. After the division into two subsamples considering the median value of the M˙ in the full sample, we find that the scatter decreases significantly for the highly accreting subsample. In particular, the smallest scatter of σrms=0.17 dex is associated with the independent parameter RFe II, followed by the combination with Fvar with σrms=0.19 dex. Both of these independent observationally inferred parameters are in turn correlated with M˙ and Lbol/LEdd . These results suggest that the large scatter along the R-L relation is driven mainly by the accretion rate intensity.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...903...86M/abstract

Autorzy: Petrucci, P. -O.; Gronkiewicz, D.; Rozanska, A.; Belmont, R.; Bianchi, S.; Czerny, B.; Matt, G.; Malzac, J.; Middei, R.; De Rosa, A.; Ursini, F.; Cappi, M.

Czasopismo: Astronomy & Astrophysics, 2020, 635, A85

A soft X-ray excess above the 2-10 keV power-law extrapolation is generally observed in the X-ray spectra of active galactic nuclei. The origin of this excess is still not well understood. Presently there are two competitive models: blurred ionized reflection and warm Comptonization. In the case of warm Comptonization, observations suggest a corona temperature in the range 0.1-2 keV and a corona optical depth of about 10-20. Moreover, radiative constraints from spectral fits with Comptonization models suggest that most of the accretion power should be released in the warm corona and the disk below is basically non-dissipative, radiating only the reprocessed emission from the corona. However, the true radiative properties of such a warm and optically thick plasma are not well known. For instance, the importance of the Comptonization process, the potential presence of strong absorption and/or emission features, and the spectral shape of the output spectrum have been studied only very recently. Here, we present simulations of warm and optically thick coronae using the TITAN radiative transfer code coupled with the NOAR Monte-Carlo code, the latter fully accounting for Compton scattering of continuum and lines. Illumination from above by hard X-ray emission and from below by an optically thick accretion disk are taken into account, as well as (uniform) internal heating. Our simulations show that for a large part of the parameter space, the warm corona with sufficient internal mechanical heating is dominated by Compton cooling and neither strong absorption nor emission lines are present in the outgoing spectra. In a smaller part of the parameter space, the calculated emission agrees with the spectral shape of the observed soft X-ray excess. Remarkably, this also corresponds to the conditions of radiative equilibrium of an extended warm corona covering a non-dissipative accretion disk almost entirely. These results confirm that warm Comptonization is a valuable model that can explain the origin of the soft X-ray excess.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020A%26A...634A..85P/abstract

Autorzy: Panda, Swayamtrupta; Martínez-Aldama, Mary Loli; Marinello, Murilo; Czerny, Bożena; Marziani, Paola; Dultzin, Deborah

Czasopismo: Astrophysical Journal, 2020, 902, 76

Optical Fe II emission is a strong feature in quasar spectra originating in the broad-line region (BLR). The difficulty in understanding the complex Fe II pseudo-continuum has led us to search for other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modeling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two spectral features with our photoionization models using CLOUDY. Taking into account the effect of dust into our modeling, we constrain the BLR parameter space (primarily in terms of the ionization parameter and local cloud density) as a function of the strengths of Fe II and Ca II emission.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020ApJ...902...76P/abstract

Autorzy: Naddaf, Mohammad-Hassan; Czerny, Bożena; Szczerba, Ryszard

Czasopismo: Frontiers in Astronomy and Space Sciences, 7, 15

Location of Broad Line Region (BLR) or inner radius of BLR in active galaxies (AGN) i.e. where the dust evaporates immediately upon departure from the accretion disk (AD) surface, scales with the source absolute luminosity. Therefore by determining this location either observationally through reverberation mapping or theoretically, one can use AGNs as an interesting laboratory to test cosmological models (Watson et al., 2011; Haas et al., 2011). In this report we focus on the theoretical side of BLR. By simulating the dynamics of matter in BLR through a realistic parametric model of AD we investigate how the Eddington ratio determines the size or in other words the radial extension and geometrical height of the BLR under different values of the model parameters.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020FrASS...7...15N/abstract

Autorzy: Panda, S.; Marziani, P.; Czerny, B.

Czasopismo: Contributions of the Astronomical Observatory Skalnaté Pleso, 2020, 50, 293

We address the effect of viewing angle of the accretion disk plane and the geometry of the broad line region (BLR) with the goal of interpreting the distribution of quasars along the main sequence (MS). We utilize photoionization code CLOUDY to model the BLR FeII emission, incorporating the grossly underestimated role of the form factor (f). We recover the dependence of the strength of the FeII emission in the optical (RFeII) on Lbol/LEdd ratio and related observational trends - as a function of the spectral energy distribution (SED) shape, cloud density, composition and intra-cloud dynamics, assumed following prior observational constraints. With this approach, we are now able to explain the diversity of quasars and the change of the quasar properties along the Main Sequence (MS). Our approach also explains the rarity of the highest FeII emitters known as the extreme xA sources and can be used as a predictive tool in future reverberation mapping studies of Type-1 AGNs. This approach further justifies the use of quasars as `cosmological probes'.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2020CoSka..50..293P/abstract

Autorzy: Czerny, Bozena

Czasopismo: 2019, Nature, 573, 354

A galaxy has been seen producing strong, regular bursts of X-rays that recur on timescales of hours. The eruptions imply that the matter flowing onto the galaxy's central black hole undergoes repeated restructuring.

Pełen tekst pracy dostępny na stronie: https://www.nature.com/articles/d41586-019-02652-y

Autorzy: Wildy, Conor; Czerny, Bożena; Panda, Swayamtrupta

Czasopismo: Astronomy & Astrophysics, 2019, 632, A41

Context. A quasar main sequence is widely believed to reveal itself through objects represented in a plane spanned by two parameters: the full width at half maximum (FWHM) of Hβ and the ratio of Fe II to Hβ equivalent width. This sequence is related to the application to quasar properties of principal component analysis (PCA), which reveals that the main axis of variance (eigenvector 1) is codirectional with a strong anticorrelation between these two measurements. Aims: We aim to determine whether the dominance of two eigenvectors, originally discovered over two decades ago, is replicated in newer high-quality quasar samples. If so, we aim to test whether a nonlinear approach is an improvement on the linear PCA method by finding two new parameters that represent a more accurate projection of the variances than the eigenvectors recovered from PCA. Methods: We selected quasars from the X-shooter archive and a major quasar catalog to build high-quality samples. These samples were tested with PCA. Results: We find that the new high-quality samples indeed have two dominant eigenvectors as originally discovered. Subsequently, we find that fitting a nonlinear decay curve to the main sequence allows a new plane spanned by linearly independent axes to be defined; this is based on the distance along the decay curve as the main axis and the distance of each quasar data point from the curve as the secondary axis, respectively. Conclusions: The results show that it is possible to define a new plane based on the quasar main sequence, which accounts for the majority of the variance. The most likely candidate for the new main axis is an anticorrelation with a black hole mass. In this case the secondary axis likely represents luminosity. However, given the results of previous studies, the inclination angle likely plays a role in the Hβ width.

Pełen tekst pracy dostępny na stronie: http://cdsads.u-strasbg.fr/abs/2018arXiv181109559C

Autorzy: Czerny, Bozena; Wang, Jian-Min; Du, Pu; Hryniewicz, Krzysztof; Karas, Vladimir; Li, Yan-Rong; Panda, Swayamtrupta; Sniegowska, Marzena; Wildy, Conor; Yuan, Ye-Fei

Czasopismo: Astrophysical Journal, 2019, 870, 84

Most results of the reverberation monitoring of active galaxies showed a universal scaling of the time delay of the Hbeta emission region with the monochromatic flux at 5100 A, with very small dipersion. Such a scaling favored the dust-based formation mechanism of the Broad Line Region (BLR). Recent reverberation measurements showed that actually a significant fraction of objects exhibits horter lags than the previously found scaling. Here we demonstrate that these shorter lags can be explained by the old concept of scaling of the BLR size with the ionization parameter. Assuming a universal value of this parameter and universal value of the cloud density reproduces the distribution of observational points in the time delay vs. monochromatic flux plane, provided that a range of black hole spins is allowed. However, a confirmation of the new measurements for low/moderate Eddington ratio sources is strongly needed before the dust-based origin of the BLR can be excluded.

Pełen tekst pracy dostępny na stronie: https://ui.adsabs.harvard.edu/abs/2019A%26A...632A..41W/abstract

Autorzy: Czerny, Bozena; Hassan Naddaf Moghaddam, Mohammad

Czasopismo: Proceedings of Science, 2019, APCS-2018, 6

We review the current status of the understanding how the accretion onto the central black hole proceeds in Active Galaxies. Standard accretion disk is a key element in all relatively bright active galaxies like Seyferts and quasars, although it is not present in very low luminosity sources, like Sgr A*. However, the standard disk does not explain the broad band spectrum, so the disk has to be supplemented with a number of additional components, and our deeper understanding of these components is still far from being complete. These additional elements are: compact hard X-ray corona, inner hot flow, warm corona, disk wind and the Broad Line Region, and finally dusty/molecular torus. All these elements seem to be needed in various proportions, depending predominantly on the Eddington ratio of a given source. These elements also interact with each other which is not yet fully taken into account.

Link do pełnego tekstu: https://arxiv.org/abs/1811.04326

Autorzy: Czerny, Bozena; Olejak, Aleksandra; Ralowski, Mateusz; Kozlowski, Szymon; Loli Martinez Aldama, Mary; Zajacek, Michal; Pych, Wojtek; Hryniewicz, Krzysztof; Pietrzynski, Grzegorz; Sobrino Figaredo, C.; and 11 coauthors

Czasopismo: Astrophysical Journal, 2019, 880, 46

We report 6 yr monitoring of distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope. We measured the rest-frame time lag of {562}-68+116 days between the continuum variations and the response of the Mg II emission line, using six different methods. This time delay, combined with other available measurements of Mg II line delay, mostly for lower-redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied Hβ line.

Link do pełnego tekstu: https://arxiv.org/abs/1901.09757

Autorzy: Peissker, F.; Zajacek, M.; Eckart, A.; Sabha, N.; Shahzamanian, B.; Parsa, M.

Czasopismo: Astronomy & Astrophysics , 2019, 624, A97

Context. We find an extended source in the direct vicinity of Sgr A* with an approximate projected mean distance of 425 ± 26 mas. Its sky-projected elongated shape can be described by an averaged spatial extension of x = 110 ± 20 mas and y = 180 ± 20 mas. With this, the observed object points in the analyzed SINFONI data sets between 2006 and 2016 directly toward the supermassive black hole. We discuss different possible scenarios that could explain the detected blueshifted line emission source. Aims: Here we present a detailed and extensive analysis of the adaptive optics corrected SINFONI data between 2006 and 2016 with a spatial pixel scale of 0.″025 and a corresponding field of view of 0.″8 × 0.″8 per single data cube with the focus on the newly discovered source. We spectroscopically identify the source, which we name X8, in the blueshifted Brγ line maps. Additionally, an upper limit for the continuum magnitude can be derived from the close-by S-star S41. Methods: We applied the standard reduction procedure with the SINFONI/EsoRex pipeline for the analysis. We applied pre- and post-data correction in order to establish various calibration procedures. For the sharpened images, we used the Lucy-Richardson algorithm with a low iteration number. For the high-pass filtered images, we used the smooth-subtracting process in order to increase the signal-to-noise ratio. Results: We are able to detect the elongated line emission source in quantified data sets between 2006 and 2016. We find a lower limit for the infrared continuum magnitude of Ks ≳ 17.0 ± 0.1. The alignment of X8 toward Sgr A* can be detected in data sets that fulfill a sufficient number of observations with a defined quality level. A more detailed analysis of the results shows indications of a bipolar outflow source that might be associated with either a young stellar object, or with a post-AGB star or young planetary nebula. Conclusions: The near-infrared excess source X8 close to S24, S25, and S41 can be detected between 2006 and 2016. In addition to an apparent bow-shock morphology, the source shows clear signatures of a bipolar outflow that is consistent with both a young stellar object and a post-AGB star. If confirmed, this would be the closest ever detected bipolar outflow source to the supermassive black hole. Similar to the case of the DSO/G2 source and other dusty sources, it further supports the in situ star formation in the direct vicinity of Sgr A*. If X8 were a bow-shock source, it would be the third object of this type that can be found in projection in the mini-cavity. This scenario would support the idea that the cavity is created by a wind from Sgr A*.

Link do pełnego tekstu: https://arxiv.org/abs/1903.05986

Autorzy: Czerny, Bozena

Czasopismo: Open Astronomy, 2019, 28, 200

Broad Emission Lines are the most characteristic features of Active Galaxies, but the mechanism of creating a medium able to emit these intense lines is not quite clear. Observations clearly indicate that the motion of the material is predominantly Keplerian, with traces of inflow and clear signatures of outflow, but this still does not point out whether the lines partially come from the disk surface, or exclusively from the circumnuclear material, and whether this material originates from the disk as a wind, or comes, at least partially, from outside. I review the basic scenarios for the formation of the Broad Line Region (BLR), and the recent progress in modelling the physical conditions in the emitting medium. The current state is the the outer radius of the BLR is fixed by the dust sublimation temperature in the medium exposed to the irradiation from the central source, the inner radius is likely fixed by the dust sublimation temperature in the atmosphere of the non-illuminated accretion disk, and the local cloud density is a universal number fixed by the radiation pressure confinement. The time-dependent aspects of the BLR formation, however, still wait for serious modelling effort matching the quality of the observational data .

Link do pełnego tekstu: https://arxiv.org/abs/1908.00742

Autorzy: Michal Zajacek, Arman Tursunov, Andreas Eckart, SilkeBritzen, Eva Hackmann, Vladim ır Karas, Zdenek Stuchliık, Bozena Czerny, and J. Anton Zensus

Czasopismo: Journal of Physics: Conference Series, 2019, 1258, 012031

In this contribution, we summarize our results concerning the observational constraints on the electric charge associated with the Galactic centre black hole ─ Sgr A*. According to the no-hair theorem, every astrophysical black hole, including supermassive black holes, is characterized by at most three classical, externally observable parameters ─ mass, spin, and the electric charge. While the mass and the spin have routinely been measured by several methods, the electric charge has usually been neglected, based on the arguments of efficient discharge in astrophysical plasmas. From a theoretical point of view, the black hole can attain charge due to the mass imbalance between protons and electrons in fully ionized plasmas, which yields about ~ 108 C for Sgr A*. The second, induction mechanism concerns rotating Kerr black holes embedded in an external magnetic field, which leads to electric field generation due to the twisting of magnetic field lines. This electric field can be associated with the induced Wald charge, for which we calculate the upper limit of ~ 1015 C for Sgr A*. Although the maximum theoretical limit of ~ 1015 C is still 12 orders of magnitude smaller than the extremal charge of Sgr A*, we analyse a few astrophysical consequences of having a black hole with a small charge in the Galactic centre. Two most prominent ones are the effect on the X-ray bremsstrahlung profile and the effect on the position of the innermost stable circular orbit .

Link do pełnego tekstu: https://arxiv.org/abs/1812.03574

Autorzy:Martínez-Aldama, Mary Loli; Czerny, Bożena; Kawka, Damian; Karas, Vladimir; Panda, Swayamtrupta; Zajacek, Michal; Zycki, Piotr T.

Czasopismo: Astrophysical Jornal, 2019, 883, 170

Quasars have been proposed as a new class of standard candles analogous to supernovae, since their large redshift range and high luminosities make them excellent candidates. The reverberation mapping (RM) method enables one to estimate the distance to the source from the time delay measurement of the emission lines with respect to the continuum, since the time delay depends on the absolute luminosity of the source. The radius-luminosity relation exhibits a low scatter and offers a potential use in cosmology. However, in recent years, the inclusion of new sources, particularly the super-Eddington accreting QSO, has increased the dispersion in the radius-luminosity relation, with many objects showing time delays shorter than the expected. Using 117 H β reverberation-mapped active galactic nuclei with 0.002 < z < 0.9 and 41.5 < log L 5100 < 45.9, we find a correction for the time delay based on the dimensionless accretion rate (\dot{{\mathscr{M}}}) considering a virial factor anticorrelated with the FWHM of H β. This correction decreases the scattering of the accretion parameters compared with the typical values used, which is directly reflected by suppressing the radius-luminosity relation dispersion. We also confirm the anticorrelation between the excess of variability and the accretion parameters. With this correction, we are able to build the Hubble diagram and estimate the cosmological constants Ω m and ΩΛ, which are consistent with the Λ Cold Dark Matter model at 2σ confidence level. Therefore, reverberation mapping results can be used to constrain cosmological models in the future.

Link do pełnego tekstu: https://arxiv.org/abs/1903.09687

Autorzy:Panda, Swayamtrupta; Marziani, Paola; Czerny, Bożena

Czasopismo: Astrophysical Jornal, 2019, 882, 79

We address the effect of orientation of the accretion disk plane and the geometry of the broad-line region (BLR) as part of an effort to understand the distribution of quasars in optical plane of the quasar main sequence. We utilize the photoionization code CLOUDY to model the BLR incorporating the grossly underestimated form factor (f). Treating the aspect of viewing angle appropriately, we confirm the dependence of the R Fe II sequence on L/{L}Edd} and on the related observational trends—as a function of the SED shape, cloud density, and composition, verified from prior observations. Sources with R Fe II in the range 1-2 (about 10% of all quasars, the so-called extreme Population A [xA] quasars) are explained as sources of high, and possibly extreme Eddington ratio along the R Fe II sequence. This result has important implications for the exploitation of xA sources as distance indicators for cosmology. Fe II emitters with R Fe II > 2 are very rare (<1% of all type 1 quasars). Our approach also explains the rarity of these highest Fe II emitters as extreme xA sources, and constrains the viewing angle ranges with increasing Hβ FWHM.

Link do pełnego tekstu: https://arxiv.org/abs/1905.01729

Autorzy:M. Zajacek, B. Czerny, M.-L. Martinez Aldama, V. Karas

Czasopismo: Astronomische Nachrichten, 2019, 340, 577

By applying different statistically robust methods, we analyze the time lag between the continuum and ionized line-emission (Mg II line) light curves for the distant bright quasar CTS C30.10 (redshift z̃0.9). The data were obtained by the 10-meter South African Large Telescope (SALT) telescope in South Africa. In detail, we demonstrate the application of several methods using the interpolated cross-correlation function (ICCF), discrete correlation function (DCF), z-transformed discrete correlation function (zDCF), von Neumann estimator, and the JAVELIN code package. In particular, we discuss the uncertainties of these methods. In conclusion, we find that the quasar lies on the broad-line region (BLR) size—monochromatic luminosity power-law scaling, RBLR∝L51001>/2, which was already confirmed for low-redshift sources. In case, the BLR size-luminosity relation holds for other distant sources, quasars could be used to probe cosmological models as "standard candles" complementary to supernovae Ia.

Link do pełnego tekstu: https://arxiv.org/abs/1907.03910

Autorzy: B. Czerny

Czasopismo: Universe, 2019, 5, 131

Slim accretion disks idea emerged over 30 years ago as an answer to several unsolved problems. Since that time there was a tremendous increase in the amount of observational data where this model applies. However, many critical issues on the theoretical side remain unsolved, as they are inherently difficult. This is the issue of the disk stability under the radiation pressure, the role of the magnetic field in the energy transfer inside the disk and the formation (or not) of a warm corona, and outflows. Thus the progress has to be done both through further developments of the model and through the careful comparison to the observational data.

Link do pełnego tekstu: https://arxiv.org/abs/1905.00120

Autorzy: Panda, Swayamtrupta; Czerny, Bożena; Done, Chris; Kubota, Aya

Czasopismo: Astrophysical Journal, 2019, 875, 133

Bright active galaxies show a range of properties, but many of these properties are correlated, which has led to the concept of the quasar main sequence. We test whether our current understanding of the quasar structure allows the pattern observed in the optical plane formed by the kinematic line width of Hβ and the relative importance of the Fe II optical emission to be reproduced. We performed simulations of the Hβ and Fe II production using the code CLOUDY and well-justified assumptions about the broadband spectra, distance to the emission line region, and the cloud properties. We show that the presence of the warm corona is an important element of the broadband spectrum, which decreases the dependence of the relative Fe II emissivity on the Eddington ratio and allows the rare cases of particularly strong Fe II emitters to be reproduced. Results are sensitive to the adopted cloud distance, and strong Fe II emission can be obtained either by adopting strongly supersolar metallicity or a much shorter distance than traditionally obtained from reverberation mapping. We modeled in a similar way the UV plane defined by the Mg II line and Fe II UV pseudo-continuum, but here our approach is less successful, in general overproducing the Fe II strength. We found that the Fe II optical and UV emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the broad-line region clouds.

Link do pełnego tekstu: https://arxiv.org/abs/1901.02962

Autorzy: Panda, Swayamtrupta; Martinez Aldama, Mary Loli; Zajacek, Michal

Czasopismo: Frontiers in Astronomy and Space Sciences, 2019, 6, 75

Reverberation mapping technique (RM) is an important milestone that has elevated our understanding of Active Galactic Nuclei (AGN) demographics, giving information about the kinematics and the structure of the Broad Line Region (BLR). It is based on the time-delay response between the continuum and the emission line. The time delay is directly related to the size of the BLR which in turn is related to the continuum luminosity of the source, producing the well-known Radius-Luminosity (RL) relation. The majority of the sources with RM data have been monitored for their Hβ emission line in low redshift sources (z<0.1), while there are some attempts using the MgII line for higher redshift ranges. In this work, we present a recent MgII monitoring for the quasar CTS C30.10 (z=0.90) observed with the 10-meter Southern African Large Telescope (SALT), for which the RL scaling based on MgII holds within measurement and time-delay uncertainties. One of the most important advantages of reverberation mapping technique is the independent determination to the distant source, and considering the large range of redshifts and luminosities found in AGNs their use in cosmological studies is promising. However, recently it has been found that highly accreting sources show the time delays shorter than expected from the RL relation. We have proposed a correction for this effect using a sample of 117 Hβ reverberating-mapped AGN with 0.02

Link do pełnego tekstu: https://arxiv.org/abs/1909.05572

Autorzy: Michal Zajacek and Arman Tursunov

Czasopismo: Observatory, 2019, 139, 231

We discuss the problem of the third black hole parameter, an electric charge. While the mass and the spin of black holes are frequently considered in the majority of publications, the charge is often neglected and implicitly set identically to zero. However, both classical and relativistic processes can lead to a small non-zero charge of black holes. When dealing with neutral particles and photons, zero charge is a good approximation. On the other hand, even a small charge can significantly influence the motion of charged particles, in particular cosmic rays, in the vicinity of black holes. Therefore, we stress that more attention should be paid to the problem of a black-hole charge and hence, it should not be neglected a priori, as it is done in most astrophysical studies nowadays. The paper looks at the problem of the black-hole charge mainly from the astrophysical point of view, which is complemented by a few historical as well as philosophical notes when relevant. In particular, we show that a cosmic ray or in general elementary charged particles passing a non-neutral black hole can experience an electromagnetic force as much as sixteen times the gravitational force for the mass of the Galactic centre black hole and its charge being seventeen orders of magnitude less than the extremal value (calculated for a proton). Furthermore, a Kerr-Newman rotating black hole with the maximum likely charge of 1 Coulomb per solar mass can have the position of its innermost stable circular orbit (ISCO) moved by both rotation and charge in ways that can enhance or partly cancel each other, putting the ISCO not far from the gravitational radius or out at more than 6 gravitational radii. An interpretation of X-ray radiation from near the ISCO of a black hole in X-ray binaries is then no longer unique.

Link do pełnego tekstu: https://arxiv.org/abs/1904.04654

Autorzy: S. Britzen, C. Fendt, M. Böttcher, M. Zajacek, F. Jaron, I. N. Pashchenko, A. Araudo,V. Karas, and O. Kurtanidze

Czasopismo:Astronomy & Astrophysics, 2019, 630, A103

Context. The neutrino event IceCube-170922A appears to originate from the BL Lac object TXS 0506+056. To understand the neutrino creation process and to localize the emission site, we studied the radio images of the jet at 15 GHz. Aims: Other BL Lac objects show properties similar to those of TXS 0506+056, such as multiwavelength variability or a curved jet. However, to date only TXS 0506+056 has been identified as neutrino emitter. The aim of this paper is to determine what makes the parsec-scale jet of TXS 0506+056 specific in this respect. Methods: We reanalyzed and remodeled 16 VLBA 15 GHz observations between 2009 and 2018. We thoroughly examined the jet kinematics and flux-density evolution of individual jet components during the time of enhanced neutrino activity between September 2014 and March 2015, and in particular before and after the neutrino event. Results: Our results suggest that the jet is very strongly curved and most likely observable under a special viewing angle of close to zero. We may observe the interaction between jet features that cross each other's paths. We find subsequent flux-density flaring of six components passing the likely collision site. In addition, we find a strong indication for precession of the inner jet, and model a precession period of about 10 yr via the Lense-Thirring effect. We discuss an alternative scenario, which is the interpretation of observing the signature of two jets within TXS 0506+056, again hinting toward a collision of jetted material. We essentially suggest that the neutrino emission may result from the interaction of jetted material in combination with a special viewing angle and jet precession. Conclusions: We propose that the enhanced neutrino activity during the neutrino flare in 2014-2015 and the single EHE neutrino IceCube-170922A could have been generated by a cosmic collision within TXS 0506+056. Our findings seem capable of explaining the neutrino generation at the time of a low gamma-ray flux and also indicate that TXS 0506+056 might be an atypical blazar. It seems to be the first time that a potential collision of two jets on parsec scales has been reported and that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.

Link do pełnego tekstu: https://www.aanda.org/articles/aa/abs/2019/10/aa35422-19/aa35422-19.html

Autorzy: Michal Zajacek, Gerold Busch, Mónica Valencia-S., Andreas Eckart, Silke Britzen, Lars Fuhrmann, Jana Schneeloch, Nastaran Fazeli, Kevin C. Harrington, & J. Anton Zensus

Czasopismo:Astronomy & Astrophysics, 2019, 630, A83

Context. The empirical relations between supermassive black holes and their host spheroids point towards the crucial role of galactic nuclei in affecting the properties of their hosts. A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. Aims: To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study the radio-optical properties of a large sample of extragalactic sources. In particular, we aim to study the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. Methods: To this goal, we combined flux densities from the radio FIRST survey at 1.4 GHz (with the flux density range 10 mJy ≤ F1.4 ≤ 100 mJy) for 396 SDSS sources at intermediate redshift (0.04 ≤ z ≤ 0.4) with the Effelsberg radiotelescope measurements at 4.85 GHz and 10.45 GHz. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Results: Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. Conclusions: While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with a steep radio index, high ionization ratio, and high radio loudness, (ii) sources with a flat radio index, lower ionization ratio, and intermediate radio loudness, (iii) sources with an inverted radio index, low ionization ratio, and low radio loudness. The classes (i), (ii), and (iii) cluster mainly along the transition from Seyfert to LINER sources in the optical diagnostic (Baldwin, Phillips & Telervich; BPT) diagram. We interpret these groups as a result of the recurrent nuclear-jet activity.

Link do pełnego tekstu: https://arxiv.org/abs/1906.08877

Autorzy: Paola Marziani, Ascension del Olmo, M. A. Martinez-Carballo, Mary Loli Martinez-Aldama, Giovanna M. Stirpe, C. Alenka Negrete, Deborah Dultzin, Mauro D’ Onofrio, Edi Bon, and Natasha Bon

Czasopismo:Astronomy & Astrophysics, 2019, 627, A88

Context. The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (BLR), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. Aims: We carried out an analysis of the C IVλ1549 and Hβ line profiles of 28 Hamburg-ESO high-luminosity quasars and of 48 low-z, low-luminosity sources in order to test whether the width of the high-ionization line C IVλ1549 could be correlated with Hβ and be used as a virial broadening estimator. Methods: We analyze intermediate- to high-S/N, moderate-resolution optical and near-infrared (NIR) spectra covering the redshifted C IVλ1549 and Hβ over a broad range of luminosity log L ̃ 44 - 48.5 [erg s-1] and redshift (0 - 3), following an approach based on the quasar main sequence. Results: The present analysis indicates that the line width of C IVλ1549 is not immediately offering a virial broadening estimator equivalent to Hβ. At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(C IVλ1549) for Eddington ratio (using the C IVλ1549 blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Conclusions: Great care should be used in estimating high-L black hole masses MBH from C IVλ1549 line width. However, once a corrected FWHM C IVλ1549 is used, a C IVλ1549-based scaling law can yield unbiased MBH values with respect to the ones based on Hβ with sample standard deviation ≈0.3 dex.

Link do pełnego tekstu: https://arxiv.org/abs/1905.00617

Autorzy: Pradhan, Ananta C.; Panda, Swayamtrupta; Parthasarathy, Mudumba; Murthy, Jayant; Ojha, Devendra K.

Czasopismo:Astrophysics and Space Science, 2019, 364, 181

We present the ultraviolet (UV) imaging observation of planetary nebulae (PNe) using archival data of Galaxy Evolution Explorer (GALEX). We found 358 PNe detected by GALEX in near-UV (NUV). We have compiled a catalogue of 108 extended PNe with sizes greater than 8″ and provided the angular diameters for all the 108 extended PNe in NUV and 28 in FUV from the GALEX images considering 3 σ surface brightness level above the background. Of the 108 PNe, 74 are elliptical, 24 are circular and 10 are bipolar in NUV with most being larger in the UV than in the radio, Hα or optical. We derived luminosities for 33 PNe in FUV (LFUV) and 89 PNe in NUV (LNUV) and found that most of the sources are very bright in UV. The FUV emission of the GALEX band includes contribution from prominent emission lines N IV] (1487 Å), C IV (1550 Å), and O III] (1661 Å) whereas the NUV emission includes C III] (1907 Å) and C II (2325 Å) for PNe of all excitation classes. The other emission lines seen in low excitation PNe are O IV] (1403 Å) and N III (1892 Å) in FUV, and O II (2470 Å) and Mg II (2830 Å) in NUV. Similarly the emission lines O V (1371 Å) and He II (1666 Å) strongly contribute in FUV for high and medium excitation PNe but not for low excitation PNe. A mixture of other emission lines seen in all excitation PNe. We have also provided images of 34 PNe in NUV and 9 PNe in FUV.

Link do pełnego tekstu: https://arxiv.org/abs/1905.00617

Autorzy: Panda, S.; Marziani, P.; Czerny, B.

Czasopismo: Contributions of the Astronomical Observatory Skalnaté Pleso, 2020, 50, 293

We address the effect of viewing angle of the accretion disk plane and the geometry of the broad line region (BLR) with the goal of interpreting the distribution of quasars along the main sequence (MS). We utilize photoionization code CLOUDY to model the BLR FeII emission, incorporating the grossly underestimated role of the form factor (f). We recover the dependence of the strength of the FeII emission in the optical (RFeII) on Lbol/LEdd ratio and related observational trends - as a function of the spectral energy distribution (SED) shape, cloud density, composition and intra-cloud dynamics, assumed following prior observational constraints. With this approach, we are now able to explain the diversity of quasars and the change of the quasar properties along the Main Sequence (MS). Our approach also explains the rarity of the highest FeII emitters known as the extreme xA sources and can be used as a predictive tool in future reverberation mapping studies of Type-1 AGNs. This approach further justifies the use of quasars as `cosmological probes'.

Link do pełnego tekstu: https://arxiv.org/abs/1908.07972

Autorzy: Petrucci, P. -O.; Gronkiewicz, D.; Rozanska, A.; Belmont, R.; Bianchi, S.; Czerny, B.; Matt, G.; Malzac, J.; Middei, R.; De Rosa, A.; Ursini, F.; Cappi, M.

Czasopismo: Astronomy & Astrophysics, 2020, 634, A85

A soft X-ray excess above the 2-10 keV power-law extrapolation is generally observed in the X-ray spectra of active galactic nuclei. The origin of this excess is still not well understood. Presently there are two competitive models: blurred ionized reflection and warm Comptonization. In the case of warm Comptonization, observations suggest a corona temperature in the range 0.1-2 keV and a corona optical depth of about 10-20. Moreover, radiative constraints from spectral fits with Comptonization models suggest that most of the accretion power should be released in the warm corona and the disk below is basically non-dissipative, radiating only the reprocessed emission from the corona. However, the true radiative properties of such a warm and optically thick plasma are not well known. For instance, the importance of the Comptonization process, the potential presence of strong absorption and/or emission features, and the spectral shape of the output spectrum have been studied only very recently. Here, we present simulations of warm and optically thick coronae using the TITAN radiative transfer code coupled with the NOAR Monte-Carlo code, the latter fully accounting for Compton scattering of continuum and lines. Illumination from above by hard X-ray emission and from below by an optically thick accretion disk are taken into account, as well as (uniform) internal heating. Our simulations show that for a large part of the parameter space, the warm corona with sufficient internal mechanical heating is dominated by Compton cooling and neither strong absorption nor emission lines are present in the outgoing spectra. In a smaller part of the parameter space, the calculated emission agrees with the spectral shape of the observed soft X-ray excess. Remarkably, this also corresponds to the conditions of radiative equilibrium of an extended warm corona covering a non-dissipative accretion disk almost entirely. These results confirm that warm Comptonization is a valuable model that can explain the origin of the soft X-ray excess.

Link do pełnego tekstu: https://arxiv.org/abs/2001.02026