Abstract
Estimates of magnetic fields for a number of active galactic nuclei are presented. These estimates are based on the observed polarization degrees and position angles of broad Hα lines and in the nearby continuum and on asymptotic analytical formulas for the Stokes parameters of the radiation emerging from a magnetized accretion disk (the Milne problem in a magnetized atmosphere). The characteristic observed feature of the wavelength dependence of the polarization degree inside the line—a minimum at the center and a fast increase of the position angle from one wing to another—can be explained by the superposition of resonance emission from two or more clouds located in the right (Keplerian velocity directed away from the observer) and left (Keplerian velocity directed toward the observer) parts of the orbit in the rotating magnetized accretion disk. The main component in our mechanism is the azimuthal magnetic field in the disk. The presence of a magnetic field perpendicular to the disk plane (which is usually weaker than the azimuthal field) results in the asymmetry of the distribution of the polarization degree and position angle inside the line. The inferred magnetic field strengths at the galactocentric distances where broad lines are emitted can be used to estimate the magnetic fields in the region of the centermost stable orbit and at the horizon of the central black hole, using the power-law dependence of the magnetic field strength corresponding to the standard model of the accretion disk.
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References
J. E. Smith, S. Young, A. Robinson, et al., Monthly Notices Roy. Astronom. Soc. 335, 773 (2002).
B. Punsly and Sh. Zhang, Astrophys. J. 725, 1928 (2010).
O. M. Blaes, in Accretion Discs, Jets and High-Energy Phenomena in Astrophysics, Ed. by V. Beskin, G. Henri, F. Menard, et al. (Springer, Les Houches, 2004), Vol. 78, p. 139.
N. A. Silant’ev, J. of Quant. Spectrosc. and Rad. Transf. 52, 207 (1994).
E. Agol and O. Blaes, Monthly Notices Roy. Astronom. Soc. 282, 965 (1996).
Yu. N. Gnedin and N. A. Silant’ev, Astrophys. and Space Sci. 10, 1 (1997).
V. V. Ivanov, S. I. Grachev, and V. M. Loskutov, Astronom. and Astrophys. 321, 968 (1997).
S. Poindexter, N. Morgan, and C. Kochanek, Astrophys. J. 673, 34 (2008).
N. I. Shakura and R. A. Sunyaev, Astronom. and Astrophys. 24, 337 (1973).
Y. Shen and A. Loeb, Astrophys. J. 725, 249 (2010).
A. Z. Dolginov, Yu. N. Gnedin, N. A. Silant’ev, Propagation and Polarization of Radiation in Cosmic Medium (Gordon & Breach, Basel, 1995).
N. A. Silant’ev, Astronom. and Astrophys. 383, 326 (2002).
N. A. Silant’ev, Astronom. and Astrophys. 433, 1117 (2005).
N. A. Silant’ev, M. Yu. Piotrovich, Yu. N. Gnedin, and T. M. Natsvlishvili, Astronom. and Astrophys. 507, 171 (2009).
S. Chandrasekhar, Radiative Transfer (Clarendon Press, Oxford, 1950).
R. R. J. Antonucci and J. S. Miller, Astrophys. J. 297, 621 (1985).
J. H. Krolik and M. C. Begelman, Astrophys. J. 329, 702 (1988).
C. M. Urry and P. Padovani, Publ. Astronom. Soc. Pacific 107, 803 (1995).
L.-X. Li, Astronom. and Astrophys. 392, 469 (2002).
D.-X. Wang, K. Xiao, and W.-H. Lei, Monthly Notices Roy. Astronom. Soc. 335, 655 (2002).
D.-X. Wang, R.-Y. Ma, W.-H. Lei, and G.-Z. Yao, Astrophys. J. 595, 109 (2003).
W.-M. Zhang, Y. Lu, and S.-N. Zhang, Chin. J. of Astronom. and Astrophys. 5, 347 (2005).
I. D. Novikov and K. Thorne, in Black Holes, Ed. by C. De Witt and B. De Witt (Gordon & Breach, New York, 1973).
J. H. Krolik, arXiv:astro-ph/0709.1489 (2007).
S. L. Shapiro, arXiv:astro-ph/0711.1537 (2007).
K. D. Murphy, T. Yaqoob, V. Karas, and M. Dovciak, Astrophys. J. 701, 635 (2009).
R. D. Blandford, in Active Galactic Nuclei, Ed. by T. J.-L. Courvoiseir and M. Mayor (Springer, Berlin, 1990), p. 161.
D. Garofalo, Astrophys. J. 699, 400 (2009).
P. J. Käpylä, M. J. Korpi, and A. Brandenburg, Astronom. and Astrophys. 419, 353 (2008).
A. Bonanno and V. Urpin, Astronom. and Astrophys. 473, 701 (2007).
M. V. Medvedev, Astrophys. J. 541, 811 (2000).
R.-Y. Ma, D.-X. Wang, and X.-Q. Zuo, Astronom. and Astrophys. 453, 1 (2006).
J. A. Braatz, A. S. Wilson, and C. Henkel, Astrophys. J. Suppl. 110, 321 (1997).
B. M. Peterson, L. Ferrarese, K. M. Gilbert, et al., Astrophys. J. 613, 682 (2004).
N. A. Silant’ev, Sov. Astron. 24, 195 (1980).
V. I. Pariev, E. G. Blackman, and S. A. Boldyrev, Astronom. and Astrophys. 407, 403 (2003).
N. A. Silant’ev, M. Yu. Piotrovich, Yu. N. Gnedin, and T. M. Natsvlishvili, Astron. Rep. 55, 683 (2011).
L. C. Ho, J. Darling, and J. E. Greene, Astrophys. J. Suppl. 177, 103 (2008).
V. L. Afanasiev, N. V. Borisov, Yu. N. Gnedin, et al., Astron. Lett. 37, 302 (2011).
J. E. Smith, A. Robinson, D. M. Alexander, et al., Monthly Notices Roy. Astronom. Soc. 350, 140 (2004).
J. E. Smith, A. Robinson, S. Young, et al., Monthly Notices Roy. Astronom. Soc. 359, 864 (2005).
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Original Russian Text © N.A. Silant’ev, Yu.N. Gnedin, S.D. Buliga, M.Yu. Piotrovich, T. M. Natsvlishvili, 2013, published in Astrofizicheskii Byulleten, 2013, Vol. 68, No. 1, pp. 4–26.
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Silant’ev, N.A., Gnedin, Y.N., Buliga, S.D. et al. Magnetic fields of active galactic nuclei and quasars with regions of polarized broad Hα lines. Astrophys. Bull. 68, 14–25 (2013). https://doi.org/10.1134/S1990341313010021
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DOI: https://doi.org/10.1134/S1990341313010021