Centrum Astronomiczne im. M. Kopernika

Warsaw, Poland

Centrum Astronomiczne im. M. Kopernika

Warsaw, Poland
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Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Misra R.,Inter-University Center for Astronomy and Astrophysics | Gierlinski M.,Durham University
Monthly Notices of the Royal Astronomical Society | Year: 2010

We consider implications of a possible presence of a Thomson-thick, low-temperature, plasma cloud surrounding the compact object in the binary system Cyg X-3. The presence of such a cloud was earlier inferred from the energy-independent orbital modulation of the X-ray flux and the lack of high frequencies in its power spectra. Here, we study the effect of Compton scattering by the cloud on the X-ray energy and power spectra, concentrating on the hard spectral state. The process reduces the energy of the high-energy break/cut-off in the energy spectra, which allows us to determine the Thomson optical depth. This, together with the observed cut-off in the power spectrum, determines the size of the plasma to be ∼2 × 109 cm. At this size, the cloud will be in thermal equilibrium in the photon field of the X-ray source, which yields the cloud temperature of ≃3 keV, which refines the determination of the Thomson optical depth to ∼7. At these parameters, thermal bremsstrahlung emission of the cloud becomes important as well. The physical origin of the cloud is likely to be collision of the very strong stellar wind of the companion Wolf-Rayet star with a small accretion disc formed by the wind accretion. Our model thus explains the peculiar X-ray energy and power spectra of Cyg X-3. © 2009 The Authors. Journal compilation © 2009 RAS.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Bottcher M.,North West University South Africa | Bottcher M.,Ohio University
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

We study hadronic models of broad-band emission of jets in radio-loud active galactic nuclei, and their implications for the accretion in those sources. We show that the models that account for broad-band spectra of blazars emitting in the GeV range in the sample of Böttcher et al. have highly super-Eddington jet powers. Furthermore, the ratio of the jet power to the radiative luminosity of the accretion disc is ~3000 on average and can be as high as ~105. We then show that the measurements of the radio core shift for the sample imply low magnetic fluxes threading the black hole, which rules out the Blandford-Znajek mechanism to produce powerful jets. These results require that the accretion rate necessary to power the modelled jets is extremely high, and the average radiative accretion efficiency is ~4 × 10-5. Thus, if the hadronic model is correct, the currently prevailing picture of accretion in AGNs needs to be significantly revised. Also, the obtained accretion mode cannot be dominant during the lifetimes of the sources, as the modelled very high accretion rates would result in too rapid growth of the central supermassive black holes. Finally, the extreme jet powers in the hadronic model are in conflict with the estimates of the jet power by other methods. © 2015 The Authors.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika
Monthly Notices of the Royal Astronomical Society | Year: 2014

We apply a recently developed technique of calculating the minimum jet kinetic power to the major mass ejections of the black hole binary GRS 1915+105 observed in radio wavelengths in 1994 and 1997. We derive for them the distance-dependent minimum power, and the corresponding mass flow rate and the total energy and mass content. We find that a fast increase of the jet power with the increasing distance combined with the jet power estimates based on the bolometric luminosity imply that the source distance is ≲10 kpc. If the jet in GRS 1915 contains ions, their bulk motion dominates the jet power, which was either neglected or not properly taken into account earlier. We also reconsider the parameters of the binary, and derive the current best estimates of the distance-dependent black hole mass and the inclination based on existing measurements combined with the kinematic constraints from the mass ejections. We also find that the measurement of the donor radius of Steeghs et al. implies the distance to the system of ≲10 kpc, in agreement with the estimate from the jet power. © 2014 The Author.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Stawarz L,Japan Aerospace Exploration Agency | Stawarz L,Jagiellonian University | Pjanka P.,Obserwatorium Astronomiczne Uniwersytetu Warszawskiego | Sikora M.,Centrum Astronomiczne im. M. Kopernika
Monthly Notices of the Royal Astronomical Society | Year: 2014

This is part one of our study of models of jets with distributed electron acceleration. We present here our assumptions, basic equations, and their solutions for the steady-state electron distribution. We assume the shape of the rate of electron acceleration and the dependences of its normalization and the magnetic field strength on the height along the jet. Our focus is on the hard spectral state of black hole binaries, for which we take into account that their typical radio spectra are flat. This appears to require a constant dissipation rate per unit logarithmic length and conservation of the magnetic energy flux. Our electron kinetic equation includes adiabatic and radiative losses and advection, and our photon radiative transfer equation includes synchrotron absorption and emission and Compton emission. Apart from the self-Compton process, we take into account Compton scattering of stellar and accretion photons and absorption of very high energy γ-rays by pair production on soft photons. We present a general solution of the kinetic equation with advection and radiative and adiabatic losses and an analytic solution in the case of dominant synchrotron losses in conical jets. In the following paper, we present detailed spectra resulting from our equations as applied to Cyg X-1. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Pjanka P.,Obserwatorium Astronomiczne Uniwersytetu Warszawskiego
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present simple and accurate analytical formulas for the rates of Compton scattering by relativistic electrons integrated over the energy distribution of blackbody seed photons. Both anisotropic scattering, in which blackbody photons arriving from one direction are scattered by an anisotropic electron distribution into another direction, and scattering of isotropic seed photons are considered. Compton scattering by relativistic electrons off blackbody photons from either stars or cosmic microwave background takes place, in particular, in microquasars, colliding-wind binaries, supernova remnants, interstellar medium and the vicinity of the Sun. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Malyshev D.,NASU Bogolyubov Institute for Theoretical Physics | Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Chernyakova M.,Dublin City University
Monthly Notices of the Royal Astronomical Society | Year: 2013

We have obtained measurements and upper limits on the emission of Cyg X-1 in the photon energy range of 0.03-300 GeV based on observations by Fermi. We present the results separately for the hard and soft spectral states, as well as for all of the analysed data. In the hard state, we detect a weak steady emission in the 0.1-10 GeV range with a power-law photon index of γ {minus tilde} 2.6 ± 0.2 at a 4σ statistical significance. This measurement, even if considered to be an upper limit, strongly constrains Compton emission of the steady radio jet, present in that state. The number of relativistic electrons in the jet has to be low enough for the spectral components due to Compton upscattering of the stellar blackbody and synchrotron radiation to be within the observed fluxes. If optically thin synchrotron emission of the jet is to account for the MeV tail, as implied by the recently claimed strong polarization in that energy range, the magnetic field in the jet has to be much above equipartition. The GeV-range measurements also strongly constrain models of hot accretion flows, most likely present in the hard state, in which γ -rays are produced from decay of neutral pions produced in collisions of energetic ions in an inner part of the flow. In the soft state, the obtained upper limits constrain electron acceleration in a non-thermal corona, most likely present around a blackbody accretion disc. The coronal emission above 30 MeV has to be rather weak, which is most readily explained by absorption of γ -rays in pair-producing photon-photon collisions. Then, the size of the bulk of the corona is less than a few tens of the gravitational radii. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Mikolajewska J.,Centrum Astronomiczne im. M. Kopernika | Belczynski K.,University of Warsaw | Belczynski K.,University of Texas at Brownsville
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

Cyg X-3 is a highly interesting accreting X-ray binary, emitting from the radio to high-energy gamma-rays. It consists of a compact object wind-fed by a Wolf-Rayet (WR) star, but the masses of the components and themass-loss rate have been a subject of controversies.Here, we determine its masses, inclination and themass-loss rate using our derived relationship between themass-loss rate and themass forWRstars of theWNtype, published infrared and X-ray data, and a relation between the mass-loss rate and the binary period derivative (observed to be >0 in Cyg X-3). Our obtained mass-loss rate is almost identical to that from two independent estimates and consistent with other ones, which strongly supports the validity of this solution. The found WR and compact-object masses are 10.3+3.9 -2.8 and 2.4+2.1 -1.1M⊙, respectively. Thus, our solution still allows for the presence of either a neutron star or a black hole, but the latter only with a low mass. However, the radio, infrared and X-ray properties of the system suggest that the compact object is a black hole. Such a low-mass black hole could be formed via accretion-induced collapse or directly from a supernova. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika
Astronomy and Astrophysics | Year: 2016

We discuss the idea of maximal jets introduced by Falcke & Biermann (1995, A&A, 293, 665). According to it, the maximum possible jet power in its internal energy equals the kinetic power in its rest mass. We show this result is incorrect because of an unfortunate algebraic mistake. © ESO, 2016.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika | Lubinski P.,Centrum Astronomiczne im. M. Kopernika | Sikora M.,Centrum Astronomiczne im. M. Kopernika
Monthly Notices of the Royal Astronomical Society | Year: 2012

We study the average X-ray and soft γ-ray spectrum of Cyg X-1 in the hard spectral state, using data from INTEGRAL. We compare these results with those from CGRO, and find a good agreement. Confirming previous studies, we find the presence of a high-energy MeV tail beyond a thermal-Comptonization spectrum; however, the tail is much softer and weaker than that recently published by Laurent et al. In spite of this difference, the observed high-energy tail could still be due to the synchrotron emission of the jet of Cyg X-1, as claimed by Laurent et al. In order to test this possibility, we study optically thin synchrotron and self-Compton emission from partially self-absorbed jets. We develop formalisms for calculating both emission of the jet base (which we define here as the region where the jet starts its emission) and emission of the entire jet. We require the emission to match that observed at the turnover energy. The optically thin emission is dominated by that from the jet base, and it has to become self-absorbed within it at the turnover frequency. We find this implies the magnetic field strength at the jet base of B 0 ∝ z 0 4 where z 0 is the distance of the base from the black hole centre. The value of B 0 is then constrained from below by the condition that the self-Compton emission is below an upper limit in the GeV range, and from above by the condition that the Poynting flux does not exceed the jet kinetic power. This yields B 0 of the order of ∼10 4G and the location of the jet base at ∼10 3 gravitational radii. Using our formalism, we find the MeV tail can be due to jet synchrotron emission, but this requires the electron acceleration at a rather hard power-law index, p≃ 1.3-1.6. For acceleration indices of p≳2, the amplitude of the synchrotron component is much below that of MeV tail, and its origin is likely to be due to hybrid Comptonization in the accretion flow. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Zdziarski A.A.,Centrum Astronomiczne im. M. Kopernika
Monthly Notices of the Royal Astronomical Society | Year: 2012

We study free-free absorption of radio emission by winds of massive stars. We derive formulae for the optical depth through the wind measured from a point of emission along a jet, taking into account Compton and photoionization heating and Compton, recombination, line and advection cooling. We apply the developed formalism to radio monitoring data for Cyg X-1, which allows us to obtain strong constraints on the structure of its inner jet. With the data at 15GHz, and taking into account an anisotropy of the stellar wind in Cyg X-1, we estimate the location of the peak of that emission along the jet at about one orbital separation, i.e. ∼3 × 10 12cm. Given a previous determination of the turnover frequency in Cyg X-1, this implies the location of the base of the jet at ∼10 3 gravitational radii. We also obtain corresponding results at 8.3 and 2.25GHz, which roughly follow the standard conical partially self-absorbed jet model. Furthermore, we find that the level of the orbital modulation depends on the radio flux, with the modulation being substantially stronger when the radio flux is lower. This is explained by the height of the radio emission along the jet decreasing with the decreasing radio flux, as predicted by jet models. Based on the finding of the flux-dependent orbital modulation, we are able to estimate a range of the possible changes of the form of the radio/X-ray correlation in Cyg X-1 due to free-free absorption. We also derive predictions for the orbital modulation and flux attenuation at frequencies beyond the 2.25-15GHz range. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

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