NuSTAR and XMM-Newton Observations of the Hard X-Ray Spectrum of Centaurus A
| Autor: | Fuerst, F., Mueller, C., Madsen, K. K., Lanz, L., Rivers, E., Brightman, M., Arevalo, P., Balokovic, M., Beuchert, T., Boggs, S. E., Christensen, F. E., Craig, W. W., Dauser, T., Farrah, D., Graefe, C., Hailey, C. J., Harrison, F. A., Kadler, M., King, A., Krauss, F., Madejski, G., Matt, G., Marinucci, A., Markowitz, A., Ogle, P., Ojha, R., Rothschild, R., Stern, D., Walton, D. J., Wilms, J., Zhang, W. |
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| Rok vydání: | 2015 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/0004-637X/819/2/150 |
| Popis: | We present simultaneous XMM-Newton and NuSTAR observations spanning 3-78 keV of the nearest radio galaxy, Centaurus A (Cen A). The accretion geometry around the central engine in Cen A is still debated, and we investigate possible configurations using detailed X-ray spectral modeling. NuSTAR imaged the central region of Cen A with sub-arcminute resolution at X-ray energies above 10 keV for the first time, but finds no evidence for an extended source or other off-nuclear point-sources. The XMM-Newton and NuSTAR spectra agree well and can be described with an absorbed power-law with a photon index {\Gamma} = 1.815 +/- 0.005 and a fluorescent Fe K{\alpha} line in good agreement with literature values. The spectrum does not require a high-energy exponential rollover, with a constraint of E_fold > 1 MeV. A thermal Comptonization continuum describes the data well, with parameters that agree with values measured by INTEGRAL, in particular an electron temperature kTe between ~100-300 keV, seed photon input temperatures between 5-50 eV. We do not find evidence for reflection or a broad iron line and put stringent upper limits of R < 0.01 on the reflection fraction and accretion disk illumination. We use archival Chandra data to estimate the contribution from diffuse emission, extra-nuclear point-sources, and the outer X-ray jet to the observed NuSTAR and XMM-Newton X-ray spectra and find the contribution to be negligible. We discuss different scenarios for the physical origin of the observed hard X-ray spectrum, and conclude that the inner disk is replaced by an advection-dominated accretion flow or that the X-rays are dominated by synchrotron self-Compton emission from the inner regions of the radio jet or a combination thereof. Comment: 13 pages, 6 figures, accepted for publication in ApJ |
| Databáze: | arXiv |
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