NuSTAR AND XMM-NEWTON OBSERVATIONS OF THE HARD X-RAY SPECTRUM OF CENTAURUS A

Abstract

We present simultaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (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 subarcminute resolution at X-ray energies above 10 keV for the first time, but found 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 Γ=1.815±0.005 and a fluorescent Fe Ka 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 kT e between ≈100-300 keV and seed photon input temperatures between 5 and 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.

AGN Coronae through a Jet Perspective

“…In our sample, the strongest radio sources are Cyg A, 3C 382, Cen A, 3C 390.3, 3C 273, 4C 74.26, and 3C 120. However, in individual detailed analysis of these sources, we find our reflection fractions are consistent with those published in the literature using the same NuSTAR data sets, albeit sometimes slightly lower (e.g., Madsen et al 2015;Reynolds et al 2015;Fürst et al 2016). As theses studies test for the possibility of an additional jet component but do not find a significant contribution from one, we may be underestimating the reflection fraction in a few of these sources but not by a significant amount.…”

GRS 1739-278 OBSERVED AT VERY LOW LUMINOSITY WITH XMM-NEWTON AND NuSTAR

“…The cutoffpl is continuously curving (even far below the folding energy) and does not necessarily accurately describe a Comptonization spectrum (Fürst et al 2016b;Fabian et al 2015). We therefore also tested the Comptonization model nthcomp (Zdziarski et al 1996;Życki et al 1999) and find a comparable fit with χ 2 red = 1.08 (χ 2 = 1022) for 945 d.o.f.…”

Disentangling the Circumnuclear Environs of Centaurus A. III. An Inner Molecular Ring, Nuclear Shocks, and the CO to Warm H2 Interface

“…The 2 -10 keV unabsorbed luminosity of the nucleus of Cen A is estimated to be as high as ∼ 5 × 10 41 ergs s −1 from Chandra and XMM-Newton, after correcting for the pile-up problem and adding extended emission (Evans et al 2004). Fürst et al (2016) use NuSTAR and XMM-Newton data and calculated an unabsorbed 3 -50 keV luminosity of 3.4 × 10 42 erg s −1 . The source is not resolved (the point-spread function of NuSTAR has a halfpower diameter of 60 ), but it can be argued that the jet is mainly visible in the soft X-rays and most of the high energy radiation is coming from the nucleus itself.…”