The infrared jet in Centaurus A: multiwavelength constraints on emission mechanisms and particle acceleration

Hardcastle, M. J.; Kraft, Ralph; Worrall, D. M.

doi:10.1111/j.1745-3933.2006.00146.x

Cited by 47 publications

(73 citation statements)

References 25 publications

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“…Birkinshaw et al 2007, in preparation). Cen A, for example, shows significant thermal dust emission in the mid-IR, on scales ranging from the unresolved subparsec scale (likely the torus) to much larger scale emission (Whysong & Antonucci 2004;Hardcastle et al 2006;Radomski et al 2007). …”

Section: Discussionmentioning

confidence: 96%

The Mid‐Infrared Emission of M87

Perlman

Mason

Packham

et al. 2007

ApJ

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We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared (mid-IR) from 5 to 35 m. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise ratio 15Y35 m spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed nuclear spectrum, even when contributions from the jet, necessary due to the degrading of resolution with wavelength, are included. The Spitzer data show a clear excess in the spectrum of the nucleus at wavelengths longer than 25 m, which we model as thermal emission from cool dust at a characteristic temperature of 55 AE 10 K, with an IR luminosity $10 39 ergs s À1 . Given Spitzer's few arcsecond angular resolution, the dust seen in the nuclear spectrum could be located anywhere within $5 00 (390 pc) of the nucleus. In any case, the ratio of active galactic nucleus (AGN ) thermal to bolometric luminosity indicates that M87 does not contain the IR-bright torus that classical unified AGN schemes invoke. However, this result is consistent with theoretical predictions for low-luminosity AGNs.

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Section: Discussionmentioning

confidence: 96%

The Mid‐Infrared Emission of M87

Perlman

Mason

Packham

et al. 2007

ApJ

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“…We model the electron energy spectrum using the model fitted to the radio, mid‐IR and X‐ray data by Hardcastle et al (2006), which is a broken power law in electron energy: the low‐energy electron energy index is 2.06 steepening to 3.88 at high energies, corresponding to the photon index of 2.44 measured by Hardcastle et al (2006) for the middle region of the X‐ray jet. As described above, the normalization and break energy of the electron spectrum are adjusted to keep consistency with the observed radio and X‐ray measurements.…”

Section: Modelling the Jets And Host Galaxiesmentioning

confidence: 99%

Modelling TeV γ-ray emission from the kiloparsec-scale jets of Centaurus A and M87

Hardcastle

Croston

2011

Monthly Notices of the Royal Astronomical Society

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The widespread detection of synchrotron X‐ray emission from the jets of low‐power, nearby radio galaxies implies the presence of electrons at and above TeV energies. In this paper we explore the possibility that the TeV γ‐rays detected from the radio galaxies Cen A and M87, which both have bright, well‐studied X‐ray jets, are produced at least in part by inverse‐Compton scattering of various photon fields by the high‐energy electrons responsible for the synchrotron X‐rays on kiloparsec scales. We describe a new numerical code that we have developed to carry out inverse‐Compton calculations taking account of all the relevant physics and using detailed models of the jets and the photon fields in which they are embedded, and show that existing constraints on the very high energy γ‐ray fluxes of these two objects already place significant constraints on the magnetic field strengths in the jet in Cen A. Finally, we discuss the prospects for constraints on radio galaxy jet physics that may be obtained from observations with the Cerenkov Telescope Array.

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“…2.1), the jet power that can be carried by the known particle population can be estimated. Considering the inner jet, that is the structure out to ∼3 kpc of projected length, where we know the electron distribution reasonably well (see Hardcastle et al 2006), we have a constraint on the bulk flow speed from the proper motion of the inner knots (0.5c, Hardcastle et al 2003), and we are also confident that the magnetic field cannot be much lower than the equipartition value (Hardcastle & Croston 2011). Do we require protons (thermal or relativistic) in order to transport 10 43 erg s −1 , if we make the additional assumption that the jet is not magnetically dominated?…”

Section: Constraints On Energy Density and Magnetic Fieldsmentioning

confidence: 99%

“…The approaching (i.e. northern) jet in Cen A has been traced out to a projected length of ∼5 kpc in radio and 4.5 kpc in X-rays, and from the changing properties of the X-ray emission at about 3.7 kpc from the nucleus, Hardcastle et al (2006) have alleged that the approaching jet enters the northern inner lobe at that point. Based on deep Chandra observations, Hardcastle et al (2007) have claimed that the receding jet extends out to ∼2 kpc in projection in X rays, and it also shows up on a similar scale in radio (Tingay et al 1998;Hardcastle et al 2003), albeit only discernible through a few faint knots.…”

Section: Introductionmentioning

confidence: 99%

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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The infrared jet in Centaurus A: multiwavelength constraints on emission mechanisms and particle acceleration

Abstract: The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1745-3933.2006.00146.

Cited by 47 publications

References 25 publications

The Mid‐Infrared Emission of M87

The Mid‐Infrared Emission of M87

Modelling TeV γ-ray emission from the kiloparsec-scale jets of Centaurus A and M87

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

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