The hard X-ray emission of Centaurus A

Beckmann, V.; Jean, P.; Lubiński, P.; Soldi, S.; Terrier, R.

doi:10.1051/0004-6361/201016020

Cited by 60 publications

(80 citation statements)

References 42 publications

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“…ASCA did detect thermal emission from hot gas in a region associated with the northern giant lobe (Isobe et al 2001), and most recently, Stawarz et al (2013) have claimed thermal and non-thermal X-ray detection with Suzaku of parts of the southern giant lobe, though they do not detect inverseCompton emission. INTEGRAL hard X-ray observations of Cen A's giant lobes by Beckmann et al (2011) are consistent Feain et al 2011), showing the giant lobes and the vertex and vortex filaments. The jets, inner lobes and the northern middle lobe are located in the saturated region centred on the nucleus.…”

Section: Introductionmentioning

confidence: 79%

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes

Croston

Hardcastle

et al. 2013

A&A

127

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Observations of the FR I radio galaxy Centaurus A in radio, X-ray, and gamma-ray bands provide evidence for lepton acceleration up to several TeV and clues about hadron acceleration to tens of EeV. Synthesising the available observational constraints on the physical conditions and particle content in the jets, inner lobes and giant lobes of Centaurus A, we aim to evaluate its feasibility as an ultra-high-energy cosmic-ray source. We apply several methods of determining jet power and affirm the consistency of various power estimates of ∼1 × 10 43 erg s −1 . Employing scaling relations based on previous results for 3C 31, we estimate particle number densities in the jets, encompassing available radio through X-ray observations. Our model is compatible with the jets ingesting ∼3 × 10 21 g s −1 of matter via external entrainment from hot gas and ∼7 × 10 22 g s −1 via internal entrainment from jet-contained stars. This leads to an imbalance between the internal lobe pressure available from radiating particles and magnetic field, and our derived external pressure. Based on knowledge of the external environments of other FR I sources, we estimate the thermal pressure in the giant lobes as 1.5 × 10 −12 dyn cm −2 , from which we deduce a lower limit to the temperature of ∼1.6 × 10 8 K. Using dynamical and buoyancy arguments, we infer ∼440−645 Myr and ∼560 Myr as the sound-crossing and buoyancy ages of the giant lobes respectively, inconsistent with their spectral ages. We re-investigate the feasibility of particle acceleration via stochastic processes in the lobes, placing new constraints on the energetics and on turbulent input to the lobes. The same "very hot" temperatures that allow self-consistency between the entrainment calculations and the missing pressure also allow stochastic UHECR acceleration models to work.

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Section: Introductionmentioning

confidence: 79%

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes

Croston

Hardcastle

et al. 2013

A&A

127

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“…Among radio loud objects, the radio galaxies seem to show rather intermediate variability amplitudes between the blazars and the radio quiet class, in agreement with the idea that the jet and the coronal emissions are probably both contributing. This makes it difficult to disentangle the relative importance of these components in the hard X-ray spectra of radio galaxies, as shown, for example, in Centaurus A (Beckmann et al 2011), 3C 111 (de Jong et al 2012, and in other radio galaxies (Grandi et al 2006). Among Seyfert galaxies, there are indications that type 1.5-2 objects are slightly more variable than type 1, as already found at hard X-rays in Beckmann et al (2007a).…”

Section: Variability Of the Different Agn Classesmentioning

confidence: 99%

Long-term variability of AGN at hard X-rays

Soldi¹,

Beckmann²,

Baumgartner³

et al. 2014

A&A

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Aims. Variability at all observed wavelengths is a distinctive property of active galactic nuclei (AGN). Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by absorption along the line of sight. Characterizing the intrinsic hard X-ray variability of a large AGN sample and comparing it to the results obtained at lower X-ray energies can significantly contribute to our understanding of the mechanisms underlying the high-energy radiation. Methods. Swift/BAT provides us with the unique opportunity to follow, on time scales of days to years and with regular sampling, the 14-195 keV emission of the largest AGN sample available up to date for this kind of investigation. As a continuation of an early work using the first 9 months of BAT data, we study the amplitude of the variations and their dependence on subclass and on energy, for a sample of 110 radio quiet and radio loud AGN selected from the BAT 58-month survey. Results. About 80% of the AGN in the sample are found to exhibit significant variability on month-to-year time scales. In particular, radio loud sources are the most variable, and Seyfert 1.5−2 galaxies are slightly more variable than Seyfert 1, while absorbed and unabsorbed objects show similar timing properties. The amplitude of the variations and their energy dependence are incompatible with variability being driven at hard X-rays by changes in the absorption column density. In general, the variations in the 14-24 and 35-100 keV bands are correlated well, suggesting a common origin to the variability across the BAT energy band. However, radio quiet AGN display on average 10% larger variations at 14-24 keV than at 35-100 keV, and a softer-when-brighter behavior for most of the Seyfert galaxies with detectable spectral variability on a time scale of a month. In addition, sources with harder spectra are found to be more variable than softer ones, unlike what it is observed below 10 keV. These properties are generally consistent with a variable, in flux and shape, power law continuum, pivoting at energies > ∼ 50 keV, to which a constant reflection component is superposed. When the same time scales are considered, the timing properties of AGN at hard X-rays are comparable to those at lower energies, with at least some of the differences possibly ascribable to components contributing differently in the two energy domains (e.g., reflection, absorption).

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“…The hard power-law continuum (∼3-100 keV) can be well described by a power law with a spectral index of Γ∼1.8 with an average unabsorbed flux of 6 20 100 keV  »-10 erg cm s 10 2 1 ---, attenuated by strong absorption (typical N H values >10 23 cm −2 ) at energies below 10 keV (see, e.g., Mushotzky et al 1978;Baity et al 1981;Beckmann et al 2011;Rothschild et al 2011, and references therein). On top of the continuum a strong Fe Ka line is present, with an equivalent width of typically ∼80 eV (Markowitz et al 2007;Fukazawa et al 2011).…”

Section: Introductionmentioning

confidence: 99%

“…Using Chandra and INTEGRAL/SPI data, Burke et al (2014) come to a similar conclusion. However, Beckmann et al (2011), using all INTEGRAL instruments, do not find a significant reflection component as modeled by pexrav (Magdziarz & Zdziarski 1995) and set a 3σ upper limit of R<0.28. Here, R is the reflection fraction, which is defined as 1 for reflection off an infinite disk, i.e., a reflector covering 2π of the sky as seen from the primary X-ray source.…”

Section: Introductionmentioning

confidence: 99%

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

Fürst

Müller

Madsen

et al. 2016

ApJ

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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.

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The hard X-ray emission of Centaurus A

Cited by 60 publications

References 42 publications

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Long-term variability of AGN at hard X-rays

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

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