Six years of Fermi-LAT and multi-wavelength monitoring of the broad-line radio galaxy 3C 120: Jet dissipation at sub-parsec scales from the central engine

Y. T. Tanaka, A. Doi, Y. Inoue, C. C. Cheung, L. Stawarz, Y. Fukazawa, M. A. Gurwell, M. Tahara, Jun Kataoka, R. Itoh

    Research output: Contribution to journalArticle

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    Abstract

    We present multi-wavelength monitoring results for the broad-line radio galaxy 3C 120 in the MeV/GeV, sub-millimeter, and 43 GHz bands over 6 yr. Over the past 2 yr, the Fermi-Large Area Telescope sporadically detected 3C 120 with high significance and the 230 GHz data also suggest an enhanced activity of the source. After the MeV/GeV detection from 3C 120 in MJD 56240-56300, 43 GHz Very Long Baseline Array (VLBA) monitoring revealed a brightening of the radio core, followed by the ejection of a superluminal knot. Since we observed the γ-ray and VLBA phenomena in temporal proximity to each other, it is naturally assumed that they are physically connected. This assumption was further supported by the subsequent observation that the 43 GHz core brightened again after a γ-ray flare occurred around MJD 56560. We can then infer that the MeV/GeV emission took place inside an unresolved 43 GHz core of 3C 120 and that the jet dissipation occurred at sub-parsec distances from the central black hole (BH), if we take the distance of the 43 GHz core from the central BH as ∼0.5 pc, as previously estimated from the time lag between X-ray dips and knot ejections. Based on our constraints on the relative locations of the emission regions and energetic arguments, we conclude that the γ rays are more favorably produced via the synchrotron self-Compton process, rather than inverse Compton scattering of external photons coming from the broad line region or hot dusty torus. We also derived the electron distribution and magnetic field by modeling the simultaneous broadband spectrum.

    Original languageEnglish
    Article numberL18
    Pages (from-to)1-6
    Number of pages6
    JournalAstrophysical Journal Letters
    Volume799
    Issue number2
    DOIs
    Publication statusPublished - 2015 Feb 1

    Fingerprint

    radio galaxies
    engines
    dissipation
    engine
    radio
    Very Long Baseline Array (VLBA)
    wavelength
    rays
    monitoring
    ejection
    wavelengths
    dip
    energetics
    scattering
    magnetic field
    electron
    electron distribution
    flares
    modeling
    proximity

    Keywords

    • Galaxies: active
    • Galaxies: individual (3C 120)
    • Galaxies: jets
    • Gamma-rays: galaxies
    • Radiation mechanisms: non-thermal
    • Radio continuum: galaxies

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Six years of Fermi-LAT and multi-wavelength monitoring of the broad-line radio galaxy 3C 120 : Jet dissipation at sub-parsec scales from the central engine. / Tanaka, Y. T.; Doi, A.; Inoue, Y.; Cheung, C. C.; Stawarz, L.; Fukazawa, Y.; Gurwell, M. A.; Tahara, M.; Kataoka, Jun; Itoh, R.

    In: Astrophysical Journal Letters, Vol. 799, No. 2, L18, 01.02.2015, p. 1-6.

    Research output: Contribution to journalArticle

    Tanaka, Y. T. ; Doi, A. ; Inoue, Y. ; Cheung, C. C. ; Stawarz, L. ; Fukazawa, Y. ; Gurwell, M. A. ; Tahara, M. ; Kataoka, Jun ; Itoh, R. / Six years of Fermi-LAT and multi-wavelength monitoring of the broad-line radio galaxy 3C 120 : Jet dissipation at sub-parsec scales from the central engine. In: Astrophysical Journal Letters. 2015 ; Vol. 799, No. 2. pp. 1-6.
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    abstract = "We present multi-wavelength monitoring results for the broad-line radio galaxy 3C 120 in the MeV/GeV, sub-millimeter, and 43 GHz bands over 6 yr. Over the past 2 yr, the Fermi-Large Area Telescope sporadically detected 3C 120 with high significance and the 230 GHz data also suggest an enhanced activity of the source. After the MeV/GeV detection from 3C 120 in MJD 56240-56300, 43 GHz Very Long Baseline Array (VLBA) monitoring revealed a brightening of the radio core, followed by the ejection of a superluminal knot. Since we observed the γ-ray and VLBA phenomena in temporal proximity to each other, it is naturally assumed that they are physically connected. This assumption was further supported by the subsequent observation that the 43 GHz core brightened again after a γ-ray flare occurred around MJD 56560. We can then infer that the MeV/GeV emission took place inside an unresolved 43 GHz core of 3C 120 and that the jet dissipation occurred at sub-parsec distances from the central black hole (BH), if we take the distance of the 43 GHz core from the central BH as ∼0.5 pc, as previously estimated from the time lag between X-ray dips and knot ejections. Based on our constraints on the relative locations of the emission regions and energetic arguments, we conclude that the γ rays are more favorably produced via the synchrotron self-Compton process, rather than inverse Compton scattering of external photons coming from the broad line region or hot dusty torus. We also derived the electron distribution and magnetic field by modeling the simultaneous broadband spectrum.",
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    T1 - Six years of Fermi-LAT and multi-wavelength monitoring of the broad-line radio galaxy 3C 120

    T2 - Jet dissipation at sub-parsec scales from the central engine

    AU - Tanaka, Y. T.

    AU - Doi, A.

    AU - Inoue, Y.

    AU - Cheung, C. C.

    AU - Stawarz, L.

    AU - Fukazawa, Y.

    AU - Gurwell, M. A.

    AU - Tahara, M.

    AU - Kataoka, Jun

    AU - Itoh, R.

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    N2 - We present multi-wavelength monitoring results for the broad-line radio galaxy 3C 120 in the MeV/GeV, sub-millimeter, and 43 GHz bands over 6 yr. Over the past 2 yr, the Fermi-Large Area Telescope sporadically detected 3C 120 with high significance and the 230 GHz data also suggest an enhanced activity of the source. After the MeV/GeV detection from 3C 120 in MJD 56240-56300, 43 GHz Very Long Baseline Array (VLBA) monitoring revealed a brightening of the radio core, followed by the ejection of a superluminal knot. Since we observed the γ-ray and VLBA phenomena in temporal proximity to each other, it is naturally assumed that they are physically connected. This assumption was further supported by the subsequent observation that the 43 GHz core brightened again after a γ-ray flare occurred around MJD 56560. We can then infer that the MeV/GeV emission took place inside an unresolved 43 GHz core of 3C 120 and that the jet dissipation occurred at sub-parsec distances from the central black hole (BH), if we take the distance of the 43 GHz core from the central BH as ∼0.5 pc, as previously estimated from the time lag between X-ray dips and knot ejections. Based on our constraints on the relative locations of the emission regions and energetic arguments, we conclude that the γ rays are more favorably produced via the synchrotron self-Compton process, rather than inverse Compton scattering of external photons coming from the broad line region or hot dusty torus. We also derived the electron distribution and magnetic field by modeling the simultaneous broadband spectrum.

    AB - We present multi-wavelength monitoring results for the broad-line radio galaxy 3C 120 in the MeV/GeV, sub-millimeter, and 43 GHz bands over 6 yr. Over the past 2 yr, the Fermi-Large Area Telescope sporadically detected 3C 120 with high significance and the 230 GHz data also suggest an enhanced activity of the source. After the MeV/GeV detection from 3C 120 in MJD 56240-56300, 43 GHz Very Long Baseline Array (VLBA) monitoring revealed a brightening of the radio core, followed by the ejection of a superluminal knot. Since we observed the γ-ray and VLBA phenomena in temporal proximity to each other, it is naturally assumed that they are physically connected. This assumption was further supported by the subsequent observation that the 43 GHz core brightened again after a γ-ray flare occurred around MJD 56560. We can then infer that the MeV/GeV emission took place inside an unresolved 43 GHz core of 3C 120 and that the jet dissipation occurred at sub-parsec distances from the central black hole (BH), if we take the distance of the 43 GHz core from the central BH as ∼0.5 pc, as previously estimated from the time lag between X-ray dips and knot ejections. Based on our constraints on the relative locations of the emission regions and energetic arguments, we conclude that the γ rays are more favorably produced via the synchrotron self-Compton process, rather than inverse Compton scattering of external photons coming from the broad line region or hot dusty torus. We also derived the electron distribution and magnetic field by modeling the simultaneous broadband spectrum.

    KW - Galaxies: active

    KW - Galaxies: individual (3C 120)

    KW - Galaxies: jets

    KW - Gamma-rays: galaxies

    KW - Radiation mechanisms: non-thermal

    KW - Radio continuum: galaxies

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