Variations of the X-ray spectrum of AGN NGC 4945 from the data of INTEGRAL space mission

1Fedorova, EV, 1Zhdanov, VI
1Astronomical Observatory of Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2016, 32(4):23-35
Start Page: Extragalactic Astronomy
Language: Russian

The results of the 3...500 keV 11-year INTEGRAL monitoring of NGC 4945 are treated. To analyze them we applied a two-component spectral model, consisting of a direct nuclear emission absorbed in the compton-thick circumnuclear torus and a reprocessed one, reflected from inner torus walls. Parameters of full-time exposure spectrum are: photon index =1.6 ± 0.07, high-energy cut-off E c=1572922 keV, column density of absorbing medium N H, 1 = 5.0 1.00.9 1024 cm–2 for the direct emission and two orders lower for the reprocessed one. Both the X-ray flux and spectral shape of NGC 4945 vary. The spectral shape changes can be caused by inhomogeneities of the absorbing medium surrounding the nucleus. But in the same time there are some signs of moderate variations in high-energy range, inflicted by changes of physical conditions in the “central engine”.

Keywords: INTEGRAL space mission, NGC 4945, X-ray spectrum, “central engine”

1.B. Efron, Nontraditional Methods of Multivariate Statistical Analysis, Ed. by Yu. P. Adler and Yu. A. Koshevnik (Finansy i Statistika, Moscow, 1988) [in Russian].

2.K. A. Arnaud, “XSPEC: The first ten years,” in Astronomical Data Analysis Software and Systems V, in Ser. ASP Conference Series. 101, Ed. by G. H. Jacoby and J. Barnes (Astron. Soc. Pacif., 1996).

3.T. J.-L. Courvoisier, R. Walter, V. Beckmann, et al., “The INTEGRAL Science Data Centre (ISDC),” Astron. Astrophys. 411, L53–L58 (2003).

4.A. de Rosa, L. Bassani, P. Ubertini, et al., “An X-ray view of absorbed INTEGRAL AGN,” Astron. Astrophys. 483, 749–758 (2008).

5.C. Done, G. M. Madejski, and D. A. Smith, “NGC 4945: The brightest Seyfert 2 galaxy at 100 keV,” Astrophys. J., Lett. 463, L63 (1998).

6.E. Fedorova, V. Beckmann, A. Neronov, and S. Soldi, “Studying the long-time variability of the Seyfert 2 galaxy NGC 4388 with INTEGRAL and Swift,” Mon. Not. R. Astron. Soc. 417, 1140 (2011).

7.E. V. Fedorova and V. I. Zhdanov, “Radio quiet AGN properties vs. spin-paradigm: The case of NGC 4945,” in Galaxies: Evolution, Morphology and Dynamics, Ed. by A. Guerrera Sanchez and R. E. Delgado Marquez (Nova Sci., New York, 2012).

8.D. Garofalo, D. A. Evans, and R. M. Sambruna, “The evolution of radio-loud active galactic nuclei as a function of black hole spin,” Mon. Not. R. Astron. Soc. 406, 975 (2010).

9.L. J. Greenhill, J. M. Moran, and J. R. Herrnstein, “The distribution of H2O maser emission in the nucleus of NGC 4945,” Astrophys. J., Lett. 481, L23–L26 (1997).

10.M. Guainazzi, G. Matt, W. N. Brandt, et al., “A broad-band X-ray view of NGC 4945,” Astron. Astrophys. 356, 463–474 (2000).

11.N. Isobe, A. Kubota, K. Makishima, P. Gandhi, et al., “Discovery of a bright transient ultraluminous X-ray source, Suzaku J1305–4931 in NGC 4945,” Publ. Astron. Soc. Jpn. 60 (Sp1), S241–S250 (2008).

12.T. Itoh, C. Done, K. Makishima, et al., “Suzaku wide–band X-ray spectroscopy of the Seyfert2 AGN 4945,” Publ. Astron. Soc. Jpn. 60 (Sp1), S251–S261 (2008).

13.K. Iwasawa, H. Awaki, and T. Yaqoob, “ASCA Spectra of Seyfert 2 Galaxies: Mrk 3 and NGC 4945,” in New Horizon of X-Ray Astronomy. First Results from ASCA, Proc. Int. Conf. on X-ray Astronomy, Tokyo Metropolitan University, Tokyo, Japan, March 8–11, 1994, in Ser. Frontiers Science Series, Vol. 12, Ed. by F. Makino and T. Ohashi (Univers. Acad., Tokyo, 1994), p. 581.

14.E. Jenc and S. J. Tingay, “The sub-parsec scale radio properties of southern starburst galaxies. II. Supernova remnants, the supernova rate, and the ionised medium in the NGC 4945 starburst,” Astron. J. 137, 537 (2009).

15.P. Magdziarz and A. A. Zdziarski, “Angle-dependent Compton reflection of X-rays and gamma-rays,” Mon. Not. R. Astron. Soc. 273, 837–848 (1995).

16.A. Marinucci, G. Risaliti, E. Nardini, et al., “The unique Suzaku discovery of variability in the Compton-thick absorber in NGC 4945,” in Proc. SUZAKU 2011: Exploring the X-ray Universe: Suzaku and Beyond, Palo Alto, CA, July 20–22, 2011, in Ser. AIP Conference Proceedings, Vol. 1427 (AIP, College Park, MD, 2012), p. 141.

17.A. Marinucci, G. Risaliti, J. Wang, et al., “The X-ray reflector in NGC 4945: a time- and space-resolved portrait,” Mon. Not. R. Astron. Soc.: Lett. 423, L6 (2012).

18.M.-L. Menzel, V. Beckmann, and F. Mattana, “AGN emission processes of NGC 4945 in the X-rays and gamma-rays,” in Proc. INTEGRAL Conf. “The Extreme and Variable High Energy Sky,” Cagliari, Sept. 19–23, 2011 (PoS SISSA, 2012), p. 075.

19.M. Molina, “Broad-band spectral analysis of a complete sample of type 1 AGN detected by INTEGRAL,” PhD Thesis (Univ. Southampton, Southampton, 2009).

20.R. Morrison and D. McCammon, “Interstellar photoelectric absorption cross sections, 0.03–10 keV,” Astrophys. J. 270, 119–122 (1983).

21.C. Ricci, R. Walter, T. J.-L. Courvoisier, and S. Paltani, “Reflection in Seyfert galaxies and the unified model of AGN,” Astron. Astrophys. 532, A102 (2011).

22.G. Risaliti, “The BeppoSAX view of bright Compton-thin Seyfert 2 galaxies,” Astron. Astrophys. 386, 379–398 (2002).

23.G. Risaliti, “The physical properties of X-ray absorbers in AGNs,” in Proc. Chandra’s First Decade of Discovery, Boston, Sept. 22–25, 2009, Ed. by S. Wolk, A. Fruscione, and D. Swartz (Chandra X-ray Center, 2009), Abstract 186.

24.N. Schurch, T. Roberts, and R. Warwick, “High-resolution X-ray imaging and spectroscopy of the core of NGC 4945 with XMM-Newton and Chandra,” Mon. Not. R. Astron. Soc. 335, 241 (2002).

25.S. Soldi, V. Beckmann, L. Bassani, et al., “INTEGRAL observations of six AGN in the Galactic Plane,” Astron. Astrophys. 444, 431–441 (2005).

26.S. Soldi, V. Beckmann, N. Gehrels, S. De Jong, and P. Lubin’ski, “High-energy emission from NGC 5506, the brightest hard X-ray Narrow Line Seyfert 1 galaxy,” in Proc. Workshop “Narrow-Line Seyfert 1 Galaxies and Their Place in the Universe”, Milano, Apr. 4–6, 2011 (PoS SISSA, 2011). https://arxivorg/abs/1105.5993.

27.S. Soldi, G. Ponti, V. Beckmann, and P. Lubinski, “AGN Variability at Hard X-Rays,” in Proc. “The Extreme Sky: Sampling the Universe above 10 keV,” Otranto, Oct. 13–17, 2009 (PoS SISSA, 2010). https://arxivorg/abs/1001.4348.

28.A. S. Wilson and E. J. M. Colbert, “The difference between radio-loud and radio-quiet active galaxies,” Astrophys. J. 438, 62–71 (1995).

29.T. Yaqoob, “The nature of the Compton-thick X-ray reprocessor in NGC 4945,” Mon. Not. R. Astron. Soc. 423, 3360–3396 (2012).