arXiv subjects

Agata Różańska

Publications and source records attributed to Agata Różańska.

At least 19 recordsLinked to original sources

arXiv2026

Radiative GRMHD simulations of puffy accretion discs: Numerical versus analytical models of sub-Eddington accretion

A widely accepted picture of an accretion flow in the luminous soft spectral state of X-ray binary systems is a geometrically thin disc structure much like the classic analytic solution of Shakura& Sunyaev. Although the analytic models are troubled by instabilities and miss important aspects of physics, such as magnetic fields, they are successfully used as a framework for interpreting observational data. Here, we compare the results of general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of optically thick, mildly sub-Eddington accretion on a stellar-mass black hole (the puffy disc) with established analytic and semi-analytic accretion models in the same regime. From the simulations, we find that the accretion flow is stabilised by the magnetic field, with a puffed-up, optically thick region resembling a warm corona surrounding a denser and cooler disc core. However, the stratified vertical structure of the disc significantly influences the observational picture of such a system. We analyse the inner disc structure, flow properties, effective viscosity, and inner edge position, and compare them to the predictions of standard models. We find that the simulated discs share some similarities with the models; however, they differ in several important aspects, most notably: the photosphere is geometrically thick, the inner edge is located closer to the central black hole than the analytic models assume, the surface density is significantly lower than analytically predicted, and the effective viscosity parameter is not constant but rises steeply in the innermost region.

astro-ph.HE↗

arXiv2026

A magnetically-supported disk-corona model for Changing-Look AGN transitions

Changing-Look Active Galactic Nuclei (CLAGN) undergo dramatic spectral and luminosity transitions on timescales of months to a few years -- orders of magnitude shorter than the viscous timescale of a standard $α$-disk at the radii where the optical/UV continuum is generated, for typical supermassive black hole masses. We show that a magnetically supported disk-corona model reproduces \emph{both} the observed Eddington ratio at which changing event occurs and the observed transition duration. Using the \texttt{diskvert} code, which solves the steady vertical structure under simultaneous gas, radiation and magnetic pressure support with a self-consistent warm corona, we (i) construct thermal-viscous S-curves, and (ii) calculate the integrated thermal timescale together with the front propagation timescale. We compute a large grid of models of different black hole masses, Eddington ratios, magnetic viscosities, and disk radii, showing that magnetized disks push the S-curve knee down to an Eddington ratio of $ \approx 0.01-0.03$, and introduce a new stable branch of high luminosity solutions, while the limit-cycle timescale enters the months-to-years range for $M_\mathrm{BH} = 10^{7}-10^{9}\,\mathrm{M_\odot}$. Confronted with a sample of five CLAGN (Mkn 590, NGC 1566, IRAS 23226$-$3843, Mkn 1018, NGC 2617), the model jointly reproduces the empirical Eddington rates and the observed event durations only when the inner disk is strongly magnetized. The case of Mkn 590 is especially constraining: the recent tightly-determined transition Eddington ratio is matched by a highly magnetized disk-corona flow at small radii.

astro-ph.HE↗

arXiv2026

Optical and cm follow-ups of the Changing-Look event in Mkn 590

The Changing-Look active galactic nucleus Mkn 590 is currently in a rejuvenated state, exhibiting a contemporaneous flux rise across X-rays, UV, optical and cm wavelengths. In this study, we present three new optical spectra obtained with the Nordic Optical Telescope, alongside three 1.4 GHz continuum measurements from the Giant Meterwave Radio Telescope, acquired since Nov. 2024. We identified a clear increase in the broad hydrogen Balmer line emission in the most recent observational epochs. Additionally, the core radio flux densities appear to track the overall X-ray variability, suggesting a possible connection between the accretion flow and jet activity. Based on these data, we aim to explore the evolution of the circumnuclear gas in this source and potential links between accretion and ejection activity.

astro-ph.HE↗

arXiv2026

Weak emission line quasar SDSS J101353.45+492758.1 I. Continuum fitting

We present a broadband study of the WLQ SDSS J101353.45+492758.1, which displays a nearly featureless UV-optical spectrum with only a weak Mg II line alongside an exceptionally low X-ray flux. We model its spectral energy distribution using the relativistic thin-disk model kerrbb with a power law, and the multicomponent AGN model relagn, a physically motivated extension of agnsed incorporating warm and hot Comptonizing regions. Our fits constrain the black hole mass, accretion rate, X-ray loudness, and coronal energetics. Both approaches yield consistent BH masses of M_{BH} \approx 2 \times 10^{9} M_\odot and an Eddington accretion rate of \dot m \approx 0.1. The relagn fit including a warm Comptonizing region provides a significantly improved representation of the UV-soft X-ray continuum. The warm corona, characterized by kTe \simeq 0.20 keV, Γ \simeq 3.8, and an optical depth τ \simeq 7.26, extends to \sim 34 R_g. The hot corona appears compact and energetically suppressed, leading to an intrinsically weak X ray output with log(L_{X}/L_{bol}) \simeq -4.29, among the lowest reported for WLQs. The α_{ox} \sim 2.06 indicates the source to be in high/soft AGN spectral state. The combination of a luminous, standard disk and extremely weak hot corona suggests that this quasar hosts a highly inefficient inner coronal region. This explains its X-ray faintness and extreme deficit of high-ionization emission lines. The source may represent an AGN analog in "ultrasoft" accretion state, or a system in which the ionizing continuum is suppressed by a compact or quenched corona. Our study suggests that the source is not accreting at high Eddington ratio, highlighting the physical diversity of WLQs, and supports the view that geometric and radiative effects jointly shape their extreme spectral properties.

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arXiv2025

A constant pressure model for the warm absorber in Mrk 509

We present the analysis of 900 ks high-resolution RGS XMM-Newton observations of the nearby Seyfert galaxy Mrk 509 with the use of a self-consistent warm absorber (WA) model. We perform a physically motivated approach to the modeling of WA as a stratified medium in constant total pressure (CTP) regime. Powerful outflows are fundamental ingredients of any active galactic nuclei (AGN) structure. They may significantly affect the cosmological environment of their host galaxy. High-resolution X-ray data are best suited for outflow's studies, and the observed absorption lines on heavy elements are evidence of the physical properties of an absorbing gas. Our models allow us to fit continuum shapes bounded together with the line profiles, which gives additional constraints on the gas structure of WA in this source. In this work, we benchmark and test the CTP model on the soft X-ray spectrum of Mrk 509. A grid of synthetic absorbed spectra was computed with the photoionization code Titan assuming that the system was under CTP. As an illuminating spectral energy distribution (SED), we used the most actual multiwavelength observations available for Mrk 509. We apply these models to the high-resolution spectrum of the WA in the Mrk 509, taking into account cold/warm/hot Galactic absorption on the way to the observer. CTP gas with $\log ξ_{0} \sim 1.9$, defined on the cloud surface, fits the data well. A higher ionization component is needed for Ne X absorption. The best-fit model is optically thin with $\log N_{\rm H }= 20.456 \pm 0.016$. The lines are non-saturated, and the CTP spectral fit aligns with previous analyses of Mrk 509 with a constant density WA. The model constrains the gas density, placing the WA cloud at 0.02 pc, consistent with the inner broad line region and the thickening region of the accretion disk.

astro-ph.GA↗

arXiv2025

Markarian 590: The AGN Awakens

Changing-Look AGN (CLAGN) Mkn 590 recently underwent a sudden re-ignition, marked by substantial increases in optical/UV and X-ray continuum flux since last couple of years. Swift-XRT observations revealed the re-emergence of a soft X-ray excess (SXE) as the source transitioned from a low-flux state in July 2023 to a significantly higher flux state in October 2024. This evolution was in response to an order-of-magnitude increase in extreme-UV (EUV) continuum emission, detected by Swift-UVOT. Follow-up optical spectra from FLOYDS Faulkes confirmed the enhancement of dynamically broadened Balmer lines, He II emission, and Fe II complex. As the Eddington fraction increased by a factor of $\sim$ 20 over the last 20 months, we found clear evidence of formation of a warm corona, strongly linked to the cold accretion disc underneath. Based on our multi-wavelength study on recent data, we propose that Mkn 590 is currently becoming a Seyfert-1.2, similar to its state in 1990s.

astro-ph.HE↗

arXiv2024

Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star. II. Iron lines

Rapidly rotating neutron stars are similar to highly flattened ellipsoids. Observed spectra of flattened stars must exhibit effects of non spherical shape and the gravitational darkening. We examined in detail the influence of both effects on the observed central energies and profiles of lines of highly ionized iron, FeXXV and FeXXVI. We note that the gravitational darkening effect do not change the central energy of lines. What is important, spectra of neutron stars that rotate with different frequencies and are seen at various inclinations angles differ significantly. The appearance and the depth of lines strongly depends on the parameters like the inclination angle of the star or the frequency of the star rotation. In this paper we clearly show that the gravitational darkening effect should be included in realistic model of the atmospheres of the neutron stars.

astro-ph.HE↗

arXiv2023

Spectral and polarization properties of reflected X-ray emission from black-hole accretion discs for a distant observer: the lamp-post model

Rebirth of X-ray polarimetric instruments will have a significant impact on our knowledge of compact accreting sources. The properties of inner-accreting regions of active galactic nuclei (AGNs) or X-ray binary systems (XRBs), such as black-hole spin, their disc inclination and orientation, shape and size of their corona, can be polarimetrically studied, parallelly to the well-known X-ray spectroscopic and timing techniques. In this work, we provide a new spectropolarimetric numerical estimate of X-rays in the lamp-post coronal model for a distant observer, including a polarized reflected radiation from the accretion disc. The local disc reflection was simulated using the codes TITAN and STOKES and includes variable disc ionization as well as Monte Carlo treatment of Compton multiple scatterings. We introduce a relativistic code KYNSTOKES based on our well-tested KY package that accounts for all relativistic effects on radiation near a black hole, apart from the returning radiation, and adds a possibility of polarized coronal emission. We study the spectrum, polarization degree and polarization angle at spatial infinity for various global system parameters and we demonstrate the difference at infinity, if analytical local reflection computations are used. We newly predict that in the hard X-rays the reflected component can be 25% polarized and the total emission can be 9% polarized in the most favourable, yet realistic configurations of radio-quiet AGNs. Thus, the relativistic disc reflection remains important for the interpretation of X-ray polarimetric observations.

astro-ph.HE↗

arXiv2023

Spectral and polarization properties of reflected X-ray emission from black hole accretion discs

X-ray polarimetric missions planned for this decade will significantly enhance our knowledge of compact accreting sources. Observations of the X-ray polarization signal from active galactic nuclei (AGNs) or X-ray binary systems (XRBs) will bring new means to study inner accretion flow in these objects that, together with currently used spectroscopic and timing techniques, will help us to determine better their properties, such as their inclination, orientation, shape, and size of their corona as well as the black hole spin. In this work, we present a yet missing piece in the global polarization models of black hole accretion discs. We compute the reflected X-ray emission from the disc in a local co-moving frame using (1) the radiative transfer code TITAN to obtain the ionization structure of the disc and (2) the Monte Carlo code STOKES that incorporates the physics of absorption, re-emission, and Compton scattering to produce a complete spectropolarimetric output. We present the final Stokes parameters I, Q, and U for a set of photon-indices of the incident primary power-law radiation, the disc ionization parameters, incident and emission angles, for three independent polarization states of the incident coronal X-ray photons with a sufficient resolution in energy to allow for sharp discussion of spectral and polarization properties. We show that the spectral component matches well literature predictions. The polarization degree and angle are in agreement with analytical approximations previously appearing in reflection models and we demonstrate that the polarized reflected X-ray emission can be, locally, quite large in the 2-12 keV band.

astro-ph.HE↗

arXiv2023

Thermal instability as a constraint for warm X-ray corona in AGN

Context. Warm corona is a possible explanation for Soft X-ray Excess in Active Galactic Nuclei (AGN). This paper contains self consistent modeling of both: accretion disk with optically thick corona, where the gas is heated by magneto-rotational instability dynamo (MRI), and cooled by radiation which undergoes free-free absorption and Compton scattering. Aims. We determine the parameters of warm corona in AGN using disk-corona structure model that takes into account magnetic and radiation pressure. We aim to show the role of thermal instability (TI) as a constraint for warm, optically thick X-ray corona in AGN. Methods. With the use of relaxation code, the vertical solution of the disk driven by MRI together with radiative transfer in hydrostatic and radiative equilibrium is calculated, which allows us to point out how TI affects the corona for wide range of global parameters. Results. We show that magnetic heating is strong enough to heat upper layers of the accretion disk atmosphere, which form the warm corona covering the disk. Magnetic pressure does not remove TI caused by radiative processes operating in X-ray emitting plasma. TI disappears only in case of accretion rates higher than 0.2 of Eddington, and high magnetic field parameter $α_{\rm B}$ > 0.1. Conclusions. TI plays the major role in the formation of the warm corona above magnetically driven accretion disk in AGN. The warm, Compton cooled corona, responsible for soft X-ray excess, resulted from our model has typical temperature in the range of 0.01 - 2 keV and optical depth even up to 50, which agrees with recent observations.

astro-ph.HE↗

arXiv2022

Deep absorption in SDSS J110511.15+530806.5

We study the origin of the anomalous deep absorption in a spectrum of the SDSS J110511.15+530806.5 distant quasar (z=1.929) obtained by the Sloan Digital Sky Survey in Data Release 7 of the optical catalog. We aim to estimate the velocity of absorbing material, and we show that this material considerably affects our measurements of the black hole (BH) mass in massive quasars with the use of common virial mass estimators. The spectral shape of the quasar was modeled assuming that the accretion disk emission is influenced by a hot corona, warm skin, and absorbing material located close to the nucleus. The whole analysis was undertaken with XSPEC models and tools. The overall spectral shape was represented with the AGNSED model, while the deep absorption is well described by two Gaussians. The observed spectrum and the fitting procedure allowed us to estimate the BH mass in the quasar as $3.52 \pm 0.01 \times 10^9 M_{\odot}$, the nonzero BH spin is $a_* = 0.32 \pm 0.04$, and the accretion rate is $\dot m=0.274 \pm 0.001$. The velocities of the detected absorbers lie in the range of 6330-108135 km/s. When we consider that absorption is caused by the CIV ion, one absorber is folding toward the nucleus with a velocity of 73887 km/s. We derived a BI index of about 20300 km/s and a mass outflow rate up to 38.5 % of the source accretion rate. The high absorption observed in SDSS J110511.15+530806.5 is evidence of fast winds that place the source in the group of objects on the border with UFO (ultra-fast outflows), strong broad absorption line (BAL), and fast failed radiatively accelerated dusty outflow (FRADO). This absorption affects the BH mass measurement by two orders of magnitude as compared to virial mass estimation.

astro-ph.HE↗

arXiv2021

Orientation of the crescent image of M 87*

The first image of the black hole (BH) M 87* obtained by the Event Horizon Telescope (EHT) has the shape of a crescent extending from the E to WSW position angles, while the observed direction of the large-scale jet is WNW. Images based on numerical simulations of BH accretion flows suggest that on average the projected BH spin axis should be oriented SSW. We explore highly simplified toy models for geometric distribution and kinematics of emitting regions in the Kerr metric, perform ray tracing to calculate the corresponding images, and simulate their observation by the EHT to calculate the corresponding visibilities and closure phases. We strictly assume that (1) the BH spin vector is fixed to the jet axis, (2) the emitting regions are stationary and symmetric with respect to the BH spin, and that (3) the emissivities are isotropic in the local rest frames. Emission from the crescent sector between SSE and WSW can be readily explained in terms of an equatorial ring with either circular or plunging geodesic flows, regardless of the value of BH spin. In the case of plane-symmetric polar caps with plunging geodesic flows, the dominant image of the cap located behind the BH is sensitive to the angular momentum of the emitter. Within the constraints of our model, we have not found a viable explanation for the observed brightness of the ESE sector. Most likely, the ESE "hotspot" has been produced by a non-stationary localised perturbation in the inner accretion flow. Alternatively, it could result from locally anisotropic synchrotron emissivities. Multi-epoch and polarimetric results from the EHT will be essential to verify the theoretically expected alignment of the BH spin with the large-scale jet.

astro-ph.HE↗

arXiv2020

Accurate Treatment of Comptonization in X-ray Illuminated Accretion Disks

A large fraction of accreting black hole and neutron stars systems present clear evidence of the reprocessing of X-rays in the atmosphere of an optically-thick accretion disk. The main hallmarks of X-ray reflection include fluorescent K-shell emission lines from iron ($\sim 6.4-6.9$ keV), the absorption iron K-edge ($\sim 7-9$ keV), and a broad featureless component known as the Compton hump ($\sim 20-40$ keV). This Compton hump is produced as the result of the scattering of high-energy photons ($E \gtrsim 10$ keV) of the relatively colder electrons ($T_e \sim 10^5-10^7$ K) in the accretion disk, in combination with photoelectric absorption from iron. The treatment of this process in most current models of ionized X-ray reflection has been done using an approximated Gaussian redistribution kernel. This approach works sufficiently well up to $\sim100$ keV, but it becomes largely inaccurate at higher energies and at relativistic temperatures ($T_e\sim10^9$ K). We present new calculations of X-ray reflection using a modified version of our code XILLVER, including an accurate solution for Compton scattering of the reflected unpolarized photons in the disk atmosphere. This solution takes into account quantum electrodynamic and relativistic effects allowing the correct treatment of high photon energies and electron temperatures. We show new reflection spectra computed with this model, and discuss the improvements achieved in the reproducing the correct shape of the Compton hump, the discrepancies with previous calculations, and the expected impact of these new models in the interpretation of observational data.

astro-ph.HE↗

arXiv2019

Warm and thick corona for magnetically supported disk in GBHB

This paper is devoted to self-consistent modeling of the magnetically supported accretion disk with optically thick warm corona based on first principles. In our model, we consider the gas heating by magneto-rotational instability (MRI) dynamo. Our goal is to show that the proper calculation of the gas heating by magnetic dynamo can build up the warm, optically thick corona above the accretion disk around black hole of stellar mass. Using vertical model of the disk supported and heated by the magnetic field together with radiative transfer in hydrostatic and radiative equilibrium we developed relaxation numerical scheme which allows us to compute the transition form the disk to corona in a self consistent way. We demonstrate here that the warm (up to 5 keV), optically thick (up to 10 Thompson optical depths), Compton cooled corona can form due to the magnetic heating. Such warm corona is stronger for higher accretion rate and larger magnetic field strength. The radial extent of the warm corona is limited by the occurrence of the local thermal instability, which purely depends on radiative processes. The obtained coronal parameters are in agreement with those constrained from X-ray observations. The warm magnetically supported corona is tends to appear in the inner disk regions. It may be responsible for Soft X-ray excess seen in accreting sources. For lower accretion rates and weaker magnetic field parameters, thermal instability prevents warm corona to exist, giving rise to eventual clumpiness or ionized outflow.

astro-ph.HE↗

arXiv2019

The high energy universe at ultra-high resolution: the power and promise of X-ray interferometry

We propose the development of X-ray interferometry (XRI), to reveal the universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 $μ$as resolution at 10 Å(1.2 keV) and 20 $μ$as at 2 Å(6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH `shadow'; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ~100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft `constellation' interferometer would resolve well below 1 $μ$as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole.

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arXiv2016

Athena Wide Field Imager Key Science Drivers

The Wide Field Imager (WFI) is one of two instruments for the Advanced Telescope for High-ENergy Astrophysics (Athena). In this paper we summarise three of the many key science objectives for the WFI - the formation and growth of supermassive black holes, non-gravitational heating in clusters of galaxies, and spin measurements of stellar mass black holes - and describe their translation into the science requirements and ultimately instrument requirements. The WFI will be designed to provide excellent point source sensitivity and grasp for performing wide area surveys, surface brightness sensitivity, survey power, and absolute temperature and density calibration for in-depth studies of the outskirts of nearby clusters of galaxies and very good high-count rate capability, throughput, and low pile-up, paired with very good spectral resolution, for detailed explorations of bright Galactic compact objects.

astro-ph.IM↗

arXiv2013

XIPE: the X-ray Imaging Polarimetry Explorer

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).

astro-ph.HE↗

arXiv2008

How to estimate the distance to the Warm Absorber in AGN from photoionized models

We present a method that allows us to estimate the distance from the continuum source located in the center of AGN to the highly ionized gas called warm absorber. We compute a set of constant total pressure photoionization models compatible with the warm absorber conditions, where a metal-rich gas is irradiated by a continuum in the form of a double power-law. The first power-law is hard up to 100 keV and represents a radiation from an X-ray source, while the second power-law extends downwards from several eVs and illustrates a radiation from an accretion disk. When the ionized continuum is dominated by the soft component, the warm absorber is heated by free-free absorption, instead of Comptonization, and the transmitted spectra show different absorption line characteristics for different values of the hydrogen number density at the cloud illuminated surface. This fact results in the possibility of deriving the number density at the cloud illuminated side from observations and hence the distance to the warm absorber.

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