arXiv subjects

Andrzej A. Zdziarski

Publications and source records attributed to Andrzej A. Zdziarski.

At least 55 records · Page 3Linked to original sources

arXiv2022

The Donor of the Black-Hole X-Ray Binary MAXI J1820+070

We estimate the parameters of the donor of the accreting black-hole binary MAXI J1820+070. The measured values of the binary period, rotational and radial velocities and constraints on the orbital inclination imply the donor is a subgiant with the mass of $M_2\approx 0.49^{+0.10}_{-0.10}M_\odot$ and the radius of $R_2\approx 1.19^{+0.08}_{-0.08}R_\odot$. We re-analyze the previously obtained optical spectrum from the Gran Telescopio Canarias, and found it yields a strict lower limit on the effective temperature of $T>4200$ K. We compile optical and infrared fluxes observed during the quiescence of this system. From the minima $r$ and $i$-band fluxes found in Pan-STARSS1 Data Release 2 pre-discovery imaging and for a distance of $D\approx3$ kpc, reddening of $E(B$--$V)=0.23$ and $R_2\approx{1.11R_\odot}$, we find $T\lesssim4230$ K, very close to the above lower limit. For a larger distance, the temperature can be higher, up to about 4500 K (corresponding to a K5 spectral type, preferred by previous studies) at $D=3.5$ kpc, allowed by the Gaia parallax. We perform evolutionary calculations for the binary system and compare them to the observational constraints. Our model fitting the above temperature and radius constraints at $D\approx 3$ kpc has the mass of $0.4M_\odot$, $T\approx4200$ K and solar metallicity. Two alternative models require $D\gtrsim 3.3$--3.4 kpc at $0.4 M_\odot$, $T\approx4500$ K and half solar metallicity, and $0.5M_\odot$, $T\approx4300$ K and solar metallicity. These models yield mass transfer rates of $\sim\!\!10^{-10}M_\odot$/yr, compatible with those based on the estimated accreted mass of $\approx\!2\times 10^{25}$ g and the time between the 2018 discovery and the 1934 historical outburst.

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arXiv2022

The Composition and Power of the Jet of the Broad-Line Radio Galaxy 3C 120

We calculated the electron-positron pair production rate at the base of the jet of 3C 120 by collisions of photons from the hot accretion flow using the measurement of its average soft gamma-ray spectrum by Compton Gamma Ray Observatory. We found that this rate approximately equals the flow rate of the leptons emitting the observed synchrotron radio-to-IR spectrum of the jet core, calculated using the extended jet model following Blandford \& Konigl. This coincidence shows the jet composition is likely to be pair-dominated. We then calculated the jet power in the bulk motion of ions, and found it greatly exceeds that achievable by the magnetically arrested disk scenario for the maximum black hole spin unless the jet contains mostly pairs. Next, we found that the magnetic flux through the synchrotron-emitting jet equals the maximum poloidal flux that can thread the black hole. Finally, we compared two estimates of the magnetization parameter at the onset of the synchrotron emission and found they are in agreement only if pairs dominate the jet content.

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arXiv2022

Insight-HXMT, NuSTAR and INTEGRAL Data Show Disk Truncation in the Hard State of the Black-Hole X-Ray Binary MAXI J1820+070

We study X-ray and soft gamma-ray spectra from the hard state of the accreting black-hole binary MAXI J1820+070. We perform analysis of joint spectra from HXMT, NuSTAR and INTEGRAL. We find an overall agreement between the spectra from all three satellites. Satisfactory fits to the data require substantial spectral complexity, with our models including two Comptonization regions and their associated disk reflection, a disk blackbody and a narrow Fe K$α$ line. Our fits confirm the presence of the truncation of the reflecting optically-thick disk at least at $>$10 gravitational radii. However, we find that the HXMT data alone cannot significantly constrain the disk inner radii.

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arXiv2021

Jet Parameters in the Black-Hole X-Ray Binary MAXI J1820+070

We study the jet in the hard state of the accreting black-hole binary MAXI J1820+070. From the available radio-to-optical spectral and variability data, we put strong constraints on the jet parameters. We find while it is not possible to uniquely determine the jet Lorentz factor from the spectral and variability properties alone, we can estimate the jet opening angle ($\approx 1.5\pm1^\circ$), the distance at which the jet starts emitting synchrotron radiation ($\sim 3 \times10^{10}$cm), and the magnetic field strength there ($\sim$10$^4$G), with relatively low uncertainty, as they depend weakly on the bulk Lorentz factor. We find the breaks in the variability power spectra from radio to sub-mm are consistent with variability damping over the time scale equal to the travel time along the jet at any Lorentz factor. This factor can still be constrained by the electron-positron pair production rate within the jet base, which we calculate based on the observed X-ray/soft gamma-ray spectrum, and the jet power, required to be less than the accretion power. The minimum ($\sim$1.5) and maximum ($\sim$4.5) Lorentz factors correspond to the dominance of pairs and ions, and the minimum and maximum jet power, respectively. We estimate the magnetic flux threading the black hole and find the jet can be powered by the Blandford-Znajek mechanism in a magnetically-arrested flow accretion flow. We point out the similarity of our derived formalism to that of core shifts, observed in extragalactic radio sources.

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arXiv2021

A comment on the properties of the matter flow through the first Langrangian point

We analyse properties of the mass outflow from the Roche-lobe filling component of a semi-detached binary system. We follow the approaches published by Paczyński \& Sienkiewicz and by Lubow \& Shu, which we compare with other simplified approaches. We find that the density of the flow at $L_1$ is orders of magnitude lower than the density on the same equipotential but away from $L_1$. Furthermore, the effective cross section of the flow, after averaging over its profile of the momentum density, is much lower than some published estimates done without accounting for the averaging. Thus, the use of some simplified formulae for the density and the flow cross section can lead to overestimates of the accretion rate and of the mass contained in the $L_1$ regions by very large factors unless they are supported by simultaneous integrations of the equations of stellar structure for the outer layers of the donor.

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arXiv2021

Towards precision measurements of accreting black holes using X-ray reflection spectroscopy

Relativistic reflection features are commonly observed in the X-ray spectra of accreting black holes. In the presence of high quality data and with the correct astrophysical model, X-ray reflection spectroscopy can be quite a powerful tool to probe the strong gravity region, study the morphology of the accreting matter, measure black hole spins, and possibly test Einstein's theory of general relativity in the strong field regime. In the last decade, there has been significant progress in the development of the analysis of these features, thanks to more sophisticated astrophysical models and new observational facilities. Here we review the state-of-the-art in relativistic reflection modeling, listing assumptions and simplifications that may affect, at some level, the final measurements and may be investigated better in the future. We review black hole spin measurements and the most recent efforts to use X-ray reflection spectroscopy for testing fundamental physics.

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arXiv2021

A spectrally stratified hot accretion flow in the hard state of MAXI J1820+070

We study the structure of the accretion flow in the hard state of the black-hole X-ray binary MAXI~J1820+070 with \nicer data. The power spectra show broadband variability which can be fit with four Lorentzian components peaking at different time scales. Extracting power spectra as a function of energy enables the energy spectra of these different power spectral components to be reconstructed. We found significant spectral differences among Lorentzians, with the one corresponding to the shortest variability time scales displaying the hardest spectrum. Both the variability spectra and the time-averaged spectrum are well-modelled by a disc blackbody and thermal Comptonization, but the presence of (at least) two Comptonization zones with different temperatures and optical depths is required. The disc blackbody component is highly variable, but only in the variability components peaking at the longest time scales ($\gsim1$ s). The seed photons for the spectrally harder zone come predominantly from the softer Comptonization zone. Our results require the accretion flow in this source to be structured, and cannot be described by a single Comptonization region upscattering disc blackbody photons, and reflection from the disc.

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arXiv2021

Hybrid Comptonization and Electron-Positron Pair Production in the Black-Hole X-Ray Binary MAXI J1820+070

We study X-ray and soft gamma-ray spectra from the hard state of the accreting black-hole binary MAXI J1820+070. We perform analysis of two joint spectra from NuSTAR and INTEGRAL, covering the range of 3--650 keV, and of an average joint spectrum over the rise of the hard state, covering the 3--2200 keV range. The spectra are well modelled by Comptonization of soft seed photons. However, the distributions of the scattering electrons are not purely thermal; we find they have substantial high-energy tails, well modelled as power laws. The photon tail in the average spectrum is detected well beyond the threshold for electron-positron pair production, 511 keV. This allows us to calculate the rate of the electron-positron pair production and put a lower limit on the size of the source from pair equilibrium. At the fitted Thomson optical depth of the Comptonizing plasma, the limit is about 4 gravitational radii. If we adopt the sizes estimated by us from the reflection spectroscopy of $>$20 gravitational radii, the fractional pair abundance becomes much less than unity. The low pair abundance is confirmed by the lack of both an annihilation feature and of a pair absorption cutoff above 511 keV in the average spectrum.

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arXiv2021

Accretion Geometry in the Hard State of the Black-Hole X-Ray Binary MAXI J1820+070

We study X-ray spectra from the outburst rise of the accreting black-hole binary MAXI J1820+070. We find that models having the disk inclinations within those of either the binary or the jet imply significant changes of the accretion disk inner radius during the luminous part of the hard spectral state, with that radius changing from $>$100 to $\sim$10 gravitational radii. The main trend is a decrease with the decreasing spectral hardness. Our analysis requires the accretion flow to be structured, with at least two components with different spectral slopes. The harder component dominates the bolometric luminosity and produces strong, narrow, X-ray reflection features. The softer component is responsible for the underlying broader reflection features. The data are compatible with the harder component having a large scale height, located downstream the disk truncation radius, and reflecting mostly from remote parts of the disk. The softer component forms a corona above the disk up to some transition radius. Our findings can explain the changes of the characteristic variability time scales, found in other works, as being driven by the changes of the disk characteristic radii.

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arXiv2021

Relativistic reflection in NGC 4151

We investigate the X-ray spectrum of the Seyfert galaxy NGC 4151 using the simultaneous Suzaku/NuSTAR observation and flux-resolved INTEGRAL spectra supplemented by Suzaku and XMM observations. Our best spectral solution indicates that the narrow Fe Kalpha line is produced in Compton-thin matter at the distance of several hundred gravitational radii. In such a model, we find a weak but significant relativistic reflection from a disk truncated at about ten gravitational radii when the source is in bright X-ray states. We do not find evidence either for or against the presence of relativistic reflection in the dim X-ray state. We also rule out models with X-ray emission dominated by a source located very close to the black hole horizon, which was proposed in previous works implementing the lamp-post geometry for this source. We point out that accurate computation of the thermal Comptonization spectrum and its distortion by strong gravity is crucial in applications of the lamp-post geometry to the NuSTAR data.

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arXiv2020

The nature of the Schoenberg-Chandrasekhar limit

We present a comprehensive description of the Schönberg--Chandrasekhar (S--C) transition, which is an acceleration of the stellar evolution from the nuclear to the thermal time scales occurring when the fractional mass of the helium core reaches a critical value, about 0.1. It occurs in the 1.4 to 7 M$_\odot$ mass range due to impossibility of maintaining the thermal equilibrium after the nuclear energy sources in the core disappear. We present the distributions of the hydrogen abundance, the energy generation rate and the temperature for stars crossing that limit. We confirm that a sharp S--C limit is present for strictly isothermal cores, but it is much smoother for real stars. The way the boundary of the core is defined is important for the picture of this transition. With a strict definition of the core as the region where the helium abundance is close to null, it occurs in an extended range of the fractional core mass of roughly 0.03 to 0.11. The cause of that is a gradual core contraction causing a correspondingly gradual loss of the core isothermality with the increasing core mass. On the other hand, when using definitions allowing for some H abundance in the core, the S--C transition is found to be sharper, at the fractional core mass of between about 0.07 and 0.11. Still, it is more a smooth transition than a sharp limit. We have also searched for specific signatures of that transition, and found that it is associated with the stellar radius first decreasing and then increasing again. We have considered whether the S--C limit can be used as a diagnostic constraining the evolutionary status of accreting X-ray binaries, but found such uses unfounded.

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arXiv2020

Two major constraints on the inner radii of accretion disks

The Stefan-Boltzmann law yields a fundamental constraint on the geometry of inner accretion disks in black-hole X-ray binaries. It follows from considering the irradiating flux and the effective temperature of the inner parts of the disk, which implies that a strong quasi-thermal component with the average energy higher than that of a blackbody at the effective temperature has to be present whenever relativistic Fe K fluorescence and reflection features are observed. The apparent absence of such quasi-thermal component with the color temperature of $\sim$1 keV in high-luminosity hard states is not compatible with a strongly irradiated disk extending close to the innermost stable circular orbit. Instead, the disk should be either truncated at a relatively large radius or irradiated by a corona at a large height, which would reduce the effective temperature and bring it to an agreement with the data. We also study constraints on disk/corona models following from comparing the disk densities fitted in literature using variable-density reflection codes with those calculated by us from the ionization parameter, the luminosity and the disk inner radius. We find that the fitted densities are much higher/lower in the hard/soft state of binaries, implying significant problems with the used assumptions and methods.

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arXiv2020

Distinct accretion modes of Cygnus X-1 revealed from hard X-rays

Thanks to recurrent observations of the black hole binary Cyg X-1 carried out over 15 years the INTEGRAL satellite has collected the largest data set in the hard X-ray band for this source. We have analyzed these data, complemented by data collected by other X-ray satellites and radio flux at 15 GHz. To characterize the spectral and variability properties of the system we have examined parameters such as the hard X-ray flux, photon index and fractional variability. Our main result is that the 2D distribution of the photon index and flux determined for the 22-100 keV band forms six clusters. This result, interpreted within the Comptonization scenario as the dominant process responsible for the hard X-ray emission, leads to a conclusion that the hot plasma in Cyg X-1 takes the form of six specific geometries. The distinct character of each of these plasma states is reinforced by their different X-ray and radio variability patterns. In particular, the hardest and softest plasma states show no short-term flux - photon index correlation typical for the four other states, implying a lack of interaction between the plasma and accretion disk. The system evolves between these two extreme states, with the spectral slope regulated by a variable cooling of the plasma by the disk photons.

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arXiv2020

Correlations and lags between X-ray and radio emission of Cyg X-1

Cygnus X-1 is a Galactic black-hole binary and a microquasar. Its X-ray emission originates most likely in the accretion flow, while the radio emission is from a magnetized jet. We study long-term cross-correlations between its X-ray and radio fluxes, searching for lags of the peak of the correlation. We use soft X-ray data from the All Sky Monitor on board of Rossi X-ray Timing Explorer, hard X-ray data from the Burst Alert Telescope on board of Neil Gehrels Swift, and 15 GHz radio monitoring data from the Ryle and AMI telescopes, which light curves cover all of the spectral states of Cyg X-1. Previous studies of radio/X-ray correlations in black-hole binaries concentrated on the soft X-ray/radio correlation in the hard spectral state. In contrast, our strongest correlation is between the hard X-rays and radio in the entire data at a $\lesssim 1$-day lag. This indicates the jet formation from a hard X-ray emitting corona/hot accretion flow through all states of Cyg X-1. We also find evidence for a long lag of the radio with respect to the soft X-rays in the soft state. This indicates long-term advection of the magnetic field through the accretion disc from its high-mass donor, which is similar to the case of another microquasar with a high-mass donor, Cyg X-3.

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arXiv2020

The persistent radio jet coupled to hard X-rays in the soft state of Cyg X-1

We study long-term radio/X-ray correlations in Cyg X-1. We find the persistent existence of a compact radio jet in its soft state. This represents a new phenomenon in black-hole binaries, in addition to compact jets in the hard state and episodic ejections of ballistic blobs in the intermediate state. While the radio emission in the hard state is strongly correlated with both the soft and hard X-rays, the radio flux in the soft state is not directly correlated with the flux of the dominant disk blackbody in soft X-rays, but instead it is lagged by about a hundred days. We interpret the lag as occurring in the process of advection of the magnetic flux from the donor through the accretion disk. On the other hand, the soft-state radio flux is very tightly correlated with the hard X-ray, 15--50 keV, flux without a measurable lag and at the same rms. This implies that the X-ray emitting disk corona and the soft-state jet are powered by the same process, probably magnetically.

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arXiv2020

Spectral and temporal properties of Compton scattering by mildly relativistic thermal electrons

We have obtained new solutions and methods for the process of thermal Comptonization. We modify the solution to the kinetic equation of Sunyaev \& Titarchuk to allow its application up to mildly relativistic electron temperatures and optical depths $\gtrsim{1}$. The solution can be used for spectral fitting of X-ray spectra from astrophysical sources. We also have developed an accurate Monte Carlo method for calculating spectra and timing properties of thermal-Comptonization sources. The accuracy of our kinetic-equation solution is verified by comparison with the Monte Carlo results. We also compare our results with those of other publicly available methods. Furthermore, based on our Monte Carlo code, we present distributions of the photon emission times and the evolution of the average photon energy for both up and down-scattering.

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arXiv2019

Jets in the soft state in Cyg X-3 caused by advection of the donor magnetic field and unification with low-mass X-ray binaries

The high-mass accreting binary Cyg X-3 is distinctly different from low-mass X-ray binaries (LMXBs) in having powerful radio and $γ$-ray emitting jets in its soft spectral state. However, the transition from the hard state to the soft one is first associated with quenching of the hard-state radio emission, as in LMXBs. The powerful soft-state jets in Cyg X-3 form, on average, $\sim$50 d later. We interpret the initial jet quenching as due to the hard-state vertical magnetic field quickly diffusing away in the thin disc extending to the innermost stable circular orbit in the soft state, or, if that field is produced in situ, also cessation of its generation. The subsequent formation of the powerful jets occurs due to advection of the magnetic field from the donor. We find this happens only above certain threshold accretion rate associated with appearance of magnetically driven outflows. The $\sim$50 d lag is of the order of the viscous timescale in the outer disc, while the field advection is much faster. This process does not happen in LMXBs due to the magnetic fluxes available from their donors being lower than that for the wind accretion from the Wolf-Rayet donor of Cyg X-3. In our model, the vertical magnetic field in the hard state, required to form the jets both in Cyg X-3 and LMXBs, is formed in situ rather than advected from the donor. Our results provide a unified scenario of the soft and hard states in both Cyg X-3 and LMXBs.

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arXiv2019

Radiative Properties of Magnetically-Arrested Disks

Magnetically-arrested disks (MADs) appear when accretion flows are supplied with a sufficient amount of magnetic flux. In this work, we use results of magnetohydrodynamic simulations to set the configuration of the magnetic field and investigate the dynamics and radiative properties of the resulting accretion flow (i.e., without that of the jet) of MAD. The method developed here is applied to both the MAD and the standard and normal evolution (SANE) accretion flow with or without large scale magnetic fields. For the radiative processes, we include synchrotron, bremsstrahlung and Compton scattering. We find that, in general, MAD accretion flows have similar spectra to those of the SANE, which complicates the task of distinguishing MADs from SANEs. At the same accretion rates, MADs are systematically brighter than SANEs. However, the critical accretion rate above which the hot solution ceases to exist is lower in MAD. Consequently, the maximum luminosity the MAD can reach is comparable but slightly lower than that of SANE, and the dependence on the magnetic flux is weak. We then discuss implications of our results for active galactic nuclei and accreting black-hole binaries.

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