Detection of Inverse-Compton X-Rays from Lobes of the Radio Galaxy Fornax A

Kaneda, Hidehiro; Tashiro, M.; Ikebe, Y.; Ishisaki, Yoshitaka; Kubo, H.; Makishima, Kazuo; Ohashi, T.; Saito, Yoshitaka; Tabara, H.; Takahashi, Tadayuki

doi:10.1086/309742

Cited by 68 publications

(36 citation statements)

References 13 publications

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“…They argued that the most likely origin of the diffuse X-ray halo, best fitted by a power-law model with the photon index Γ X 1.88 ± 0.19, is inverse-Compton emission of the non-thermal electrons within the lobes interacting with the cosmic microwave background (CMB) photon field. This detection, which is only the second of its kind following the case of Fornax A (Feigelson et al 1995;Kaneda et al 1995), was followed by a number of analogous studies targeting other radio galaxies with the XMM-Newton, Suzaku, and Chandra X-ray satellites (Kataoka & Stawarz 2005;Croston et al 2005;Isobe et al 2011, and references therein). For Centaurus B, the Chandra observations resolved the inner parts of the main (SW) jet at arcsec scale, thanks to its excellent spatial resolution (Marshall et al 2005).…”

Section: Introductionmentioning

confidence: 89%

Fermi-LAT andSuzakuobservations of the radio galaxy Centaurus B

Katsuta

Tanaka

Stawarz

et al. 2013

A&A

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Centaurus B is a nearby radio galaxy positioned in the southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the γ-ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ray data. We confirm its detection at GeV photon energies and analyze the extension and variability of the γ-ray source in the LAT dataset, in which it appears as a steady γ-ray emitter. The X-ray core of Centaurus B is detected as a bright source of a continuum radiation. We do not detect, however, any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and γ-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed γ-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. In this case, the observed γ-ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. By means of synchrotron self-Compton modeling, we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.

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Section: Introductionmentioning

confidence: 89%

Fermi-LAT andSuzakuobservations of the radio galaxy Centaurus B

Katsuta

Tanaka

Stawarz

et al. 2013

A&A

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“…Feigelson et al 1995), ASCA (e.g., Kaneda et al 1995;Tashiro et al 1998Tashiro et al , 2001, Chandra (e.g., Isobe et al 2002;Croston et al 2005;Yaji et al 2010), XMM-Newton (e.g., Isobe et al 2005Isobe et al , 2006 and Suzaku (Isobe et al , 2011a indicate a dominance of the electron energy density U e over the magnetic one U B by typically an order of magnitude in many RG lobes (see Croston et al 2005;Isobe et al 2009Isobe et al , 2011a, even though several lobes are also found in almost equipartition condition U e = U B (see, e.g., discussion in Isobe et al 2011a).…”

Section: Introductionmentioning

confidence: 99%

The energetics of giant radio galaxy lobes from inverse Compton scattering observations

Colafrancesco

Marchegiani

2011

A&A

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Context. Giant radio galaxy (GRG) lobes are excellent laboratories for studying the evolution of the particle and magnetic field energetics and the past activity of radiogalaxy jets, as indicated by recent results of X-ray observations with Suzaku. However, these results are based on assumptions of the shape and extension of the GRG lobe electron spectrum. Aims. We re-examine the energetics of GRG lobes as derived by inverse Compton scattering of cosmic microwave background (CMB) photons (ICS-CMB) by relativistic electrons in RG lobes to assess the realistic physical conditions of RG lobes, their energetics, and their radiation regime. We consider the steep-spectrum GRG DA 240 recently observed by Suzaku as a reference case and we also discuss other RG lobes observed with Chandra and XMM. Methods. We model the spectral energy distribution (SED) of the GRG DA 240 East lobe to obtain constraints on the shape and on the extension of the electron spectrum by using multi-frequency information from radio to gamma-rays. We use radio and X-ray data to constrain the shape and normalization of the electron spectrum and we then calculate the Sunyaev-Zel'dovich (SZ) effect expected in GRG lobes that is sensitive to the total electron energy density. Results. We show that the electron energy density U e derived form X-ray observations can yield only a rough lower limit to its actual value and that most of the estimates of U e based on X-ray measurements have to be increased even by a large factor by considering realistic estimates of the lower electron momentum p 1 . This moves RG lobes away from the equipartition condition toward a particledominated and Compton power dominance regime. We propose to use the distribution of RG lobes in the U e /U B vs. U e /U CMB plane as another divide divide between the different physical regimes of particle and field dominance and radiation mechanism dominance in RG lobes. Conclusions. We conclude that the SZ effect produced by ICS-CMB mechanism observable in RG lobes provides reliable estimate of p 1 and U e and is the best tool to determine the total energy density of RG lobes and to assess their physical regime. This observational tool is available with the sensitive high-frequency radio and mm experiments.

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“…Motivated by the pioneering discoveries of lobe IC X-rays with ROSAT and ASCA from Fornax A (Feigelson et al 1995;Kaneda et al 1995;Tashiro et al 2001) and Centaurus B , several subsequent studies with Chandra (e.g., Croston et al 2005;Kataoka & Stawarz 2005) and XMM-Newton (e.g., Isobe et al 2005Isobe et al , 2006Migliori et al 2007) proved the usefulness of this technique. Moreover, such research has revealed an electron dominance of u e /u m = 1-10 typically in lobes of moderate radio galaxies (e.g., Croston et al 2005).…”

Section: Introductionmentioning

confidence: 99%

SUZAKUOBSERVATION OF THE GIANT RADIO GALAXY 3C 326

Isobe

Tashiro

Gandhi

et al. 2009

ApJ

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A Suzaku observation of a giant radio galaxy, 3C 326, which has a physical size of about 2 Mpc, was conducted on 2008 January 19-21. In addition to several X-ray sources, diffuse emission was significantly detected and associated with its west lobe, but the east lobe was contaminated by an unidentified X-ray source WARP J1552.4+2007. After careful evaluation of the X-ray and non-X-ray background, the 0.4-7 keV X-ray spectrum of the west lobe is described by a power-law model modified with the Galactic absorption. The photon index and 1 keV flux density were derived as Γ = 1.82 +0.26 −0.24 ± 0.04 and S X = 19.4 +3.3 −3.2 ± 3.0 nJy, respectively, where the first and second errors represent the statistical and systematic ones. The diffuse X-rays were attributed to be inverse Compton (IC) radiation by the synchrotron radio electrons scattering off the cosmic microwave background photons. This radio galaxy is the largest among those with lobes detected through IC X-ray emission. A comparison of the radio to X-ray fluxes yields the energy densities of electron and magnetic field as u e = (2.3 ± 0.3 ± 0.3) × 10 −13 erg cmand u m = (1.2 +0.2 −0.1 ± 0.2) × 10 −14 erg cm −3 , respectively. The galaxy is suggested to host a low-luminosity nucleus with an absorption-corrected 2-10 keV luminosity of < 2 × 10 42 erg s −1 , together with a relatively weak radio core. The energetics in the west lobe of 3C 326 were compared with those of moderate radio galaxies with a size of ∼100 kpc. The west lobe of 3C 326 is confirmed to agree with the correlations for the moderate radio galaxies, u e ∝ D −2.2±0.4 and u m ∝ D −2.4±0.4 , where D is their total physical size. This implies that the lobes of 3C 326 are still being energized by the jet, despite the current weakness of the nuclear activity.

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Detection of Inverse-Compton X-Rays from Lobes of the Radio Galaxy Fornax A

Cited by 68 publications

References 13 publications

Fermi-LAT andSuzakuobservations of the radio galaxy Centaurus B

Fermi-LAT andSuzakuobservations of the radio galaxy Centaurus B

The energetics of giant radio galaxy lobes from inverse Compton scattering observations

SUZAKUOBSERVATION OF THE GIANT RADIO GALAXY 3C 326

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