SUZAKU observations of the diffuse X-ray emission across the Fermi Bubbles' edges

Jun Kataoka, M. Tahara, T. Totani, Y. Sofue, Stawarz, Y. Takahashi, Y. Takeuchi, H. Tsunemi, M. Kimura, Y. Takei, C. C. Cheung, Y. Inoue, T. Nakamori

    Research output: Contribution to journalArticle

    53 Citations (Scopus)

    Abstract

    We present Suzaku X-ray observations along two edge regions of the Fermi Bubbles, with eight ≃ 20 ks pointings across the northern part of the North Polar Spur (NPS) surrounding the north bubble and six across the southernmost edge of the south bubble. After removing compact X-ray features, diffuse X-ray emission is clearly detected and is well reproduced by a three-component spectral model consisting of unabsorbed thermal emission (temperature kT ≃ 0.1 keV) from the Local Bubble, absorbed kT ≃ 0.3 keV thermal emission related to the NPS and/or Galactic halo (GH), and a power-law component at a level consistent with the cosmic X-ray background. The emission measure (EM) of the 0.3 keV plasma decreases by ≃ 50% toward the inner regions of the northeast bubble, with no accompanying temperature change. However, such a jump in the EM is not clearly seen in the south bubble data. While it is unclear whether the NPS originates from a nearby supernova remnant or is related to previous activity within or around the Galactic center, our Suzaku observations provide evidence that suggests the latter scenario. In the latter framework, the presence of a large amount of neutral matter absorbing the X-ray emission as well as the existence of the kT ≃ 0.3 keV gas can be naturally interpreted as a weak shock driven by the bubbles' expansion in the surrounding medium, with velocity v exp ∼ 300 km s-1 (corresponding to shock Mach number ), compressing the GH gas to form the NPS feature. We also derived an upper limit for any non-thermal X-ray emission component associated with the bubbles and demonstrate that, in agreement with the aforementioned findings, the non-thermal pressure and energy estimated from a one-zone leptonic model of its broadband spectrum, are in rough equilibrium with that of the surrounding thermal plasma.

    Original languageEnglish
    Article number57
    JournalAstrophysical Journal
    Volume779
    Issue number1
    DOIs
    Publication statusPublished - 2013 Dec 10

    Fingerprint

    North Polar Spur (astronomy)
    bubble
    bubbles
    x rays
    galactic halos
    thermal emission
    shock
    plasma
    thermal plasmas
    supernova remnants
    gases
    gas
    compressing
    Mach number
    power law
    temperature
    broadband
    expansion
    energy

    Keywords

    • acceleration of particles
    • cosmic rays
    • Galaxy: center
    • Galaxy: halo
    • X-rays: ISM

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Kataoka, J., Tahara, M., Totani, T., Sofue, Y., Stawarz, Takahashi, Y., ... Nakamori, T. (2013). SUZAKU observations of the diffuse X-ray emission across the Fermi Bubbles' edges. Astrophysical Journal, 779(1), [57]. https://doi.org/10.1088/0004-637X/779/1/57

    SUZAKU observations of the diffuse X-ray emission across the Fermi Bubbles' edges. / Kataoka, Jun; Tahara, M.; Totani, T.; Sofue, Y.; Stawarz; Takahashi, Y.; Takeuchi, Y.; Tsunemi, H.; Kimura, M.; Takei, Y.; Cheung, C. C.; Inoue, Y.; Nakamori, T.

    In: Astrophysical Journal, Vol. 779, No. 1, 57, 10.12.2013.

    Research output: Contribution to journalArticle

    Kataoka, J, Tahara, M, Totani, T, Sofue, Y, Stawarz, Takahashi, Y, Takeuchi, Y, Tsunemi, H, Kimura, M, Takei, Y, Cheung, CC, Inoue, Y & Nakamori, T 2013, 'SUZAKU observations of the diffuse X-ray emission across the Fermi Bubbles' edges', Astrophysical Journal, vol. 779, no. 1, 57. https://doi.org/10.1088/0004-637X/779/1/57
    Kataoka, Jun ; Tahara, M. ; Totani, T. ; Sofue, Y. ; Stawarz ; Takahashi, Y. ; Takeuchi, Y. ; Tsunemi, H. ; Kimura, M. ; Takei, Y. ; Cheung, C. C. ; Inoue, Y. ; Nakamori, T. / SUZAKU observations of the diffuse X-ray emission across the Fermi Bubbles' edges. In: Astrophysical Journal. 2013 ; Vol. 779, No. 1.
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    AU - Kataoka, Jun

    AU - Tahara, M.

    AU - Totani, T.

    AU - Sofue, Y.

    AU - Stawarz,

    AU - Takahashi, Y.

    AU - Takeuchi, Y.

    AU - Tsunemi, H.

    AU - Kimura, M.

    AU - Takei, Y.

    AU - Cheung, C. C.

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    AU - Nakamori, T.

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    N2 - We present Suzaku X-ray observations along two edge regions of the Fermi Bubbles, with eight ≃ 20 ks pointings across the northern part of the North Polar Spur (NPS) surrounding the north bubble and six across the southernmost edge of the south bubble. After removing compact X-ray features, diffuse X-ray emission is clearly detected and is well reproduced by a three-component spectral model consisting of unabsorbed thermal emission (temperature kT ≃ 0.1 keV) from the Local Bubble, absorbed kT ≃ 0.3 keV thermal emission related to the NPS and/or Galactic halo (GH), and a power-law component at a level consistent with the cosmic X-ray background. The emission measure (EM) of the 0.3 keV plasma decreases by ≃ 50% toward the inner regions of the northeast bubble, with no accompanying temperature change. However, such a jump in the EM is not clearly seen in the south bubble data. While it is unclear whether the NPS originates from a nearby supernova remnant or is related to previous activity within or around the Galactic center, our Suzaku observations provide evidence that suggests the latter scenario. In the latter framework, the presence of a large amount of neutral matter absorbing the X-ray emission as well as the existence of the kT ≃ 0.3 keV gas can be naturally interpreted as a weak shock driven by the bubbles' expansion in the surrounding medium, with velocity v exp ∼ 300 km s-1 (corresponding to shock Mach number ), compressing the GH gas to form the NPS feature. We also derived an upper limit for any non-thermal X-ray emission component associated with the bubbles and demonstrate that, in agreement with the aforementioned findings, the non-thermal pressure and energy estimated from a one-zone leptonic model of its broadband spectrum, are in rough equilibrium with that of the surrounding thermal plasma.

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