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Aperiodic X-ray flux variability of EX Hya and the area of the base of the accretion column at the white dwarf surface

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Abstract

The goal of this paper is to determine the characteristic cooling time of the accretion flowmatter near the surface of the magnetic white dwarf in the binary system EX Hya. Most of the X-ray photons in such binary systems are produced in an optically thin hot plasma with a temperature above 10 keV heated when the matter passes through the shock near the white dwarf surface. The total X-ray luminosity is determined by the matter accumulated below the shock in its cooling time. Thus, the X-ray luminosity variability related to the variations in the accretion rate onto the white dwarf surface must be suppressed at frequencies higher than the inverse cooling time. If the optically thin plasma radiation dominates in the rate of energy losses by the heated matter, which is true for white dwarfs with moderately strong magnetic fields, less than 1–10 MG, then the matter cooling time can give an estimate of the matter density in the accretion column. Given the accretion rate and the matter density in the accretion column at the white dwarf surface, the area of the accretion channel can be estimated. We have analyzed all of the currently available observational data for one of the brightest intermediate polars in the X-ray sky, EX Hya, from the RXTE and XMM-Newton observatories. The power spectra of its aperiodic variability have given an upper limit on the cooling time of the hot plasma: <1.5–2 s. For the observed accretion rate, ×1015 g s−1, this corresponds to a matter density below the shock surface ≳1016 cm−3 and an area of the base of the accretion channel no more than <4.6 × 1015 cm2. Using the information about the maximum geometrical size of the accretion channel obtained by analyzing X-ray eclipses in the binary system EX Hya, we have derived an upper limit on the thickness of the flow over the surface of the magnetosphere near the white dwarf surface, ≲3 × 106 cm, and the plasma penetration depth at the magnetospheric boundary, Δr/r ≲ 6 × 10−3.

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References

  1. K. Aizu, Progress Theor. Phys. 1184, 49 (1973).

    Google Scholar 

  2. P. J. Armitage and C. S. Reynolds, Mon.Not. R. Astron. Soc. 341, 1041 (2003).

    Article  ADS  Google Scholar 

  3. J. Arons and S. M. Lea, Astrophys. J. 207, 914 (1976).

    Article  ADS  Google Scholar 

  4. M. M. Basko and R. A. Sunyaev, Mon. Not. R. Astron. Soc. 175, 395 (1976).

    Article  ADS  Google Scholar 

  5. K.E. Belle, S. B. Howell, E.M. Sion, K. S. Long, and P. Szkody, Astrophys. J. 587, 373 (2003).

    Article  ADS  Google Scholar 

  6. K. Beuermann, T.-E. Harrison, B. E. McArthur, G. F. Benedict, B. T. Gänsicke, Astron. Astrophys. 419, 291 (2004).

    Article  ADS  Google Scholar 

  7. K. Beuermann and K. Reinsch, Astron. Astrophys. 480, 199 (2008).

    Article  ADS  Google Scholar 

  8. H. V. Bradt, R. E. Rothschild, and J. H. Swank, Astrophys. J. Suppl. Ser. 97, 355 (1993).

    ADS  Google Scholar 

  9. D. A. H. Buckley and I. R. Tuohy, Astrophys. J. 344, 376 (1989).

    Article  ADS  Google Scholar 

  10. C. G. Campbell, Geophys. Astrophys. Fluid Dynam. 63, 179 (1992).

    Article  ADS  Google Scholar 

  11. C. G. Campbell, Mon. Not. R. Astron. Soc. 403, 1339 (2010).

    Article  ADS  Google Scholar 

  12. J. B. G. Canalle, C. J. Saxton, K. Wu, M. Cropper, and G. Ramsay, Astron. Astrophys. 440, 185 (2005).

    Article  ADS  Google Scholar 

  13. G. Chanmugam and R. L. Wagner, Astrophys. J. 232, 895S (1979).

    Article  ADS  Google Scholar 

  14. G. Chanmugam, S. H. Langer, and G. Shaviv, Astrophys. J. 299, L87 (1985).

    Article  ADS  Google Scholar 

  15. E. Churazov, M. Gilfanov, and M. Revnivtsev, Mon. Not. R. Astron. Soc. 321, 759 (2001).

    Article  ADS  Google Scholar 

  16. S. Eisenbart, K. Beuermann, K. Reinsch, and B. T. Gänsicke,, Astron. Astrophys. 382, 984 (2002).

    Article  ADS  Google Scholar 

  17. P. A. Evans and C. Hellier, Mon. Not. R. Astron. Soc. 353, 447 (2004).

    Article  ADS  Google Scholar 

  18. L. Ferrario, Publ. Astron. Soc. Pacif. 13, 87 (1996).

    ADS  Google Scholar 

  19. P. Ghosh and F. K. Lamb, Astrophys. J. 223, L83 (1978).

    Article  ADS  Google Scholar 

  20. P. Ghosh and F. K. Lamb, Astrophys. J. 232, 259 (1979).

    Article  ADS  Google Scholar 

  21. J.-M. Hameury, A. R. King, and J.-P. Lasota, Mon. Not. R. Astron. Soc. 218, 695 (1986).

    Article  ADS  Google Scholar 

  22. T. E. Harrison, R. K. Campbell, S. B. Howell, F. A. Cordova, and A. D. Schwope, Astrophys. J. 656, 444 (2007).

    Article  ADS  Google Scholar 

  23. T. Hayashi, M. Ishida, Y. Terada, A. Bamba, and T. Shionome, Publ. Astron. Soc. Jpn. 63, 739 (2011).

    Article  ADS  Google Scholar 

  24. C. Hellier, EPJ Web Conf. 64, 7001 (2014).

    Article  Google Scholar 

  25. S. Hirose, J. H. Krolik, and J. M. Stone, Astrophys. J. 640, 901 (2006).

    Article  ADS  Google Scholar 

  26. S. Ichimaru, Astrophys. J. 244, 198 (1978).

    Article  ADS  Google Scholar 

  27. K. Jahoda, C. B. Markwardt, Y. Radeva, A. H. Rots, M. J. Stark, J. H. Swank, T. E. Strohmayer, and W. Zhang, Astrophys. J. Suppl. Ser. 163, 401 (2006).

    Article  ADS  Google Scholar 

  28. F. Jansen, D. Lumb, B. Altieri, J. Clavel, M. Ehle, C. Erd, C. Gabriel, M. Guainazzi, et al., Astron. Astrophys. 365, L1 (2001).

    Article  ADS  Google Scholar 

  29. J. C. Jernigan, R. I. Klein, and J. Arons, Astrophys. J. 530, 875 (2000).

    Article  ADS  Google Scholar 

  30. Y. Kim and K. Beuermann, Astron. Astrophys. 298, 165 (1995).

    ADS  Google Scholar 

  31. F. K. Lamb, C. J. Pethick, and D. Pines, Astrophys. J. 184, 271 (1973).

    Article  ADS  Google Scholar 

  32. D.-Q. Lamb and A. R. Masters, Astrophys. J. 234, L117 (1979).

    Article  ADS  Google Scholar 

  33. S. H. Langer, G. Chanmugam, and G. Shaviv, Astrophys. J. 245, L23 (1981).

    Article  ADS  Google Scholar 

  34. S. H. Langer, G. Chanmugam, and G. Shaviv, Astrophys. J. 258, 289 (1982).

    Article  ADS  Google Scholar 

  35. M. Long, M. M. Romanova, and R. V. E. Lovelace, Astrophys. J. 634, 1214 (2005).

    Article  ADS  Google Scholar 

  36. R. V. E. Lovelace, M. M. Romanova, and G. S. Bisnovatyi-Kogan, Mon. Not. R. Astron. Soc. 275, 244 (1995).

    ADS  Google Scholar 

  37. Y. E. Lyubarskii, Mon. Not. R. Astron. Soc. 292, 679 (1997).

    Article  ADS  Google Scholar 

  38. C.W. Mauche, Astrophys. J. 520, 822 (1999).

    Article  ADS  Google Scholar 

  39. S. Miyamoto, K. Kimura, S. Kitamoto, T. Dotani, and K. Ebisawa, Astrophys. J. 383, 784 (1991).

    Article  ADS  Google Scholar 

  40. K. Mukai, M. Ishida, J. Osborne, S. Rosen, and D. Stavroyiannopoulos, ASP Conf. 137, 554 (1998).

    ADS  Google Scholar 

  41. D. O’Donoghue, D. A. H. Buckley, L. A. Balona, D. Bester, L. Botha, J. Brink, D. B. Carter, et al.,Mon. Not. R. Astron. Soc. 372, 151 (2006).

    Article  ADS  Google Scholar 

  42. J. E. Pringle and M. J. Rees, Astron. Astrophys. 21, 1 (1972).

    ADS  Google Scholar 

  43. M. Revnivtsev, E. Churazov, K. Postnov, and S. Tsygankov, Astron. Astrophys. 507, 1211 (2009).

    Article  ADS  Google Scholar 

  44. M. Revnivtsev, S. Potter, A. Kniazev, R. Burenin, D. A. H. Buckley, and E. Churazov, Mon. Not. R. Astron. Soc. 411, 1317 (2011).

    Article  ADS  Google Scholar 

  45. M. M. Romanova, R. V. E. Lovelace, M. Bachetti, A. A. Blinova, A. V. Koldoba, R. Kurosawa, P. S. Lii, and G. V. Ustyugova, arXiv 1311, 4597 (2013).

  46. S. R. Rosen, Mon. Not. R. Astron. Soc. 254, 493 (1992).

    Article  ADS  Google Scholar 

  47. G. B. Rybicki and A. P. Lightman, Radiative Processes in Astrophysics (Wiley-VCH, 1986).

    Google Scholar 

  48. A. N. Semena and M.G. Revnivtsev, Astron. Lett. 38, 321 (2012).

    Article  ADS  Google Scholar 

  49. A. N. Semena, M. G. Revnivtsev, I. M. Khamitov, R. A. Burenin, T. Ak, Z. Eker, and M. N. Pavlinsky, Astron. Lett. 39, 227 (2013).

    Article  ADS  Google Scholar 

  50. A. N. Semena et al., Mon. Not. R. Astron. Soc. (2014, in press).

    Google Scholar 

  51. F. Shu, J. Najita, E. Ostriker, F. Wilkin, S. Ruden, and S. Lizano, Astrophys. J. 438, 781 (1994).

    Article  ADS  Google Scholar 

  52. N. Siegel, K. Reinsch, K. Beuermann, E. Wolff, and H. van der Woerd, Astron. Astrophys. 225, 97 (1989).

    ADS  Google Scholar 

  53. H. C. Spruit and R. E. Taam, Astron. Astrophys. 229, 475 (1990).

    ADS  Google Scholar 

  54. T. Wada, A. Shimizu, M. Suzuki, M. Kato, and R. Hoshi, Progress Theor. Phys. 64, 6 (1980).

    Google Scholar 

  55. B. Welsh, D. Anderson, J. McPhate, J. Vallerga, O. H. W. Siegmund, D. Buckley, A. Gulbis, M. Kotze, and S. Potter, IAU Symp. 285, 99 (2012).

    ADS  Google Scholar 

  56. K. Wu, H. Pongracic, G. Chanmugam, and G. Shaviv, Publ. Astron. Soc. Pacif. 13, 93 (1996).

    ADS  Google Scholar 

  57. K. Wu and C. J. Saxton, ASP Conf. 157, 317 (1999).

    ADS  Google Scholar 

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  1. Space Research Institute, Russian Academy of Sciences, Profsoyuznaya ul. 84/32, Moscow, 117997, Russia

    A. N. Semena & M. G. Revnivtsev

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Original Russian Text © A.N. Semena, M.G. Revnivtsev, 2014, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2014, Vol. 40, No. 8, pp. 529–538.

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Semena, A.N., Revnivtsev, M.G. Aperiodic X-ray flux variability of EX Hya and the area of the base of the accretion column at the white dwarf surface. Astron. Lett. 40, 475–484 (2014). https://doi.org/10.1134/S1063773714080088

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