The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations

K. Tanada, Jun Kataoka, M. Arimoto, M. Akita, C. C. Cheung, S. W. Digel, Y. Fukazawa

    Research output: Contribution to journalArticle

    4 Citations (Scopus)

    Abstract

    We present an analysis of eight years of Fermi-LAT (>0.1 GeV) γ-ray data obtained for the radio galaxy NGC 1275. The γ-ray flux from NGC 1275 is highly variable on short (∼days to weeks) timescales, and has steadily increased over this eight year timespan. By examining the changes in its flux and spectral shape in the LAT energy band over the entire data set, we found that its spectral behavior changed around 2011 February (∼MJD 55600). The γ-ray spectra at early times evolved largely at high energies, while the photon indices were unchanged at later times despite rather large flux variations. To explain these observations, we suggest that the flux changes at the early times were caused by injection of high-energy electrons into the jet while, later, the γ-ray flares were caused by a changing Doppler factor owing to variations in the jet Lorentz factor and/or changes in the angle to our line of sight. To demonstrate the viability of these scenarios, we fit the broad band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior in the context of the SSC model, the maximum electron Lorentz factor would have changed at the early times, while a modest change in the Doppler factor adequately fits the quiescent and flaring state γ-ray spectra at the later times.

    Original languageEnglish
    Article number74
    JournalAstrophysical Journal
    Volume860
    Issue number1
    DOIs
    Publication statusPublished - 2018 Jun 10

    Fingerprint

    rays
    gamma rays
    energy
    synchrotrons
    electron
    radio galaxies
    spectral energy distribution
    viability
    high energy electrons
    line of sight
    flares
    energy bands
    radio
    timescale
    injection
    broadband
    intervals
    photons
    electrons
    flaring

    Keywords

    • galaxies: active
    • galaxies: individual (NGC 1275)
    • galaxies: jets
    • galaxies: Seyfert
    • gamma rays: general
    • radiation mechanisms: non-thermal

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations. / Tanada, K.; Kataoka, Jun; Arimoto, M.; Akita, M.; Cheung, C. C.; Digel, S. W.; Fukazawa, Y.

    In: Astrophysical Journal, Vol. 860, No. 1, 74, 10.06.2018.

    Research output: Contribution to journalArticle

    Tanada, K. ; Kataoka, Jun ; Arimoto, M. ; Akita, M. ; Cheung, C. C. ; Digel, S. W. ; Fukazawa, Y. / The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations. In: Astrophysical Journal. 2018 ; Vol. 860, No. 1.
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    AB - We present an analysis of eight years of Fermi-LAT (>0.1 GeV) γ-ray data obtained for the radio galaxy NGC 1275. The γ-ray flux from NGC 1275 is highly variable on short (∼days to weeks) timescales, and has steadily increased over this eight year timespan. By examining the changes in its flux and spectral shape in the LAT energy band over the entire data set, we found that its spectral behavior changed around 2011 February (∼MJD 55600). The γ-ray spectra at early times evolved largely at high energies, while the photon indices were unchanged at later times despite rather large flux variations. To explain these observations, we suggest that the flux changes at the early times were caused by injection of high-energy electrons into the jet while, later, the γ-ray flares were caused by a changing Doppler factor owing to variations in the jet Lorentz factor and/or changes in the angle to our line of sight. To demonstrate the viability of these scenarios, we fit the broad band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior in the context of the SSC model, the maximum electron Lorentz factor would have changed at the early times, while a modest change in the Doppler factor adequately fits the quiescent and flaring state γ-ray spectra at the later times.

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