Dept. of Space Astronomy and Astrophysics

磯部 直樹

イソベ ナオキ  (Naoki Isobe)

基本情報

所属
国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙物理学研究系 助教
学位
博士(理学)(2002年3月 東京大学理学系研究科物理学専攻)

J-GLOBAL ID
202001017082346100
researchmap会員ID
R000012159

受賞

 2

主要な論文

 104
  • Naoki Isobe, Hiroshi Nagai, Motoki Kino, Shunsuke Baba, Takao Nakagawa, Yuji Sunada, Makoto Tashiro
    The Astrophysical Journal 2023年8月1日  査読有り筆頭著者
  • Yuji Sunada, Naoki Isobe, Makoto S Tashiro, Motoki Kino, Shoko Koyama, Satomi Nakahara
    Monthly Notices of the Royal Astronomical Society 512(4) 5995-6006 2022年3月25日  査読有り
    ABSTRACT The far-infrared counterpart of hotspot D, the terminal hotspot of the eastern jet hosted by the radio galaxy Cygnus A, is detected with Herschel Aperture photometry of the source performed in 5 photometric bands covering the wavelength range of 70–350 $\mu$m. After removing the contamination from another nearby hotspot, E, the far-infrared intensity of hotspot D is derived as 83 ± 13 and 269 ± 66 mJy at 160 and 350 $\mu$m, respectively. Since the far-infrared spectrum of the object smoothly connects to the radio one, the far-infrared emission is attributed to the synchrotron radiation from the radio-emitting electron population. The radio-to-near-infrared spectrum is confirmed to exhibit a far-infrared break feature at the frequency of $\nu _\mathrm{br}=2.0^{+1.2}_{-0.8} \times 10^{12}$ Hz. The change in energy index at the break (Δα = 0.5) is interpreted as the impact of radiative cooling on an electron distribution sustained by continuous injection from diffusive shock acceleration. By ascribing the derived break to this cooling break, the magnetic field, B, in the hotspot is determined as a function of its radius, R within a uniform one-zone model combined with the strong relativistic shock condition. An independent B–R constraint is obtained by assuming the X-ray spectrum is wholly due to synchrotron self-Compton emission. By combining these conditions, the two parameters are tightly determined as B = 120–150 μG and R = 1.3–1.6 kpc. A further investigation into the two conditions indicates the observed X-ray flux is highly dominated by the synchrotron self-Compton emission.
  • Naoki Isobe, Yuji Sunada, Motoki Kino, Shoko Koyama, Makoto Tashiro, Hiroshi Nagai, Chris Pearson
    The Astrophysical Journal 899(1) 17-17 2020年8月7日  査読有り筆頭著者
  • Naoki Isobe, Shoko Koyama, Motoki Kino, Takehiko Wada, Takao Nakagawa, Hideo Matsuhara, Kotaro Niinuma, Makoto Tashiro
    The Astrophysical Journal 850(2) 193-193 2017年12月1日  査読有り筆頭著者
    Mid-infrared properties are reported of the west hot spot of the radio galaxy Pictor A with the Wide-field Infrared Survey Explorer (WISE). The mid-infrared counterpart to the hot spot, WISE J051926.26-454554.1, is listed in the AllWISE source catalog. The source was detected in all four of the WISE photometric bands. A comparison between the WISE and radio images reinforces the physical association of the WISE source to the hot spot. The WISE flux density of the source was carefully evaluated. A close investigation of the multi-wavelength synchrotron spectral energy distribution from the object reveals a mid-infrared excess at the wavelength of lambda = 22 mu m with a statistical significance of 4.8 sigma over the simple power-law extrapolation from the synchrotron radio spectrum. The excess is reinforced by single and double cutoff power-law modeling of the radio-to-optical spectral energy distribution. The synchrotron cutoff frequency of the main and excess components was evaluated as 7.1 x 10(14) Hz and 5.5 x 10(13) Hz, respectively. From the cutoff frequency, the magnetic field of the emission region was constrained as a function of the region size. In order to interpret the excess component, an electron population different from the main one dominating the observed radio spectrum is necessary. The excess emission is proposed to originate in a substructure within the hot spot, in which the magnetic field is a factor of a few stronger than that in the minimum-energy condition. The relation of the mid-infrared excess to the X-ray emission is briefly discussed.
  • Naoki Isobe, Taiki Kawamuro, Shinki Oyabu, Takao Nakagawa, Shunsuke Baba, Kenichi Yano, Yoshihiro Ueda, Yoshiki Toba
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68(6) 2016年12月  
    Nearby active galactic nuclei were diagnosed in the X-ray and mid-to-far infrared wavelengths with Monitor of All-sky X-ray Image (MAXI) and the Japanese infrared observatory AKARI, respectively. One hundred of the X-ray sources listed in the second release of theMAXI all-sky X-ray source catalog are currently identified as non-blazar-type active galactic nuclei. These include 95 Seyfert galaxies and 5 quasars, and they are composed of 73 type-1 and 27 type-2 objects. The AKARI all-sky survey point source catalog was searched for their mid-and far-infrared counterparts at 9, 18, and 90 mu m. As a result, 69 Seyfert galaxies in the MAXI catalog (48 type-1 and 21 type-2) were found to be detected with AKARI. The X-ray (3-4 keV and 4-10 keV) and infrared luminosities of these objects were investigated, together with their color information. Adopting the canonical photon index, Gamma = 1.9, of the intrinsic X-ray spectrum of the Seyfert galaxies, the X-ray hardness ratio between the 3-4 and 4-10 keV ranges derived with MAXI was roughly converted into the absorption column density. After the X-ray luminosity was corrected for absorption from the estimated column density, the well-known X-ray-to-infrared luminosity correlation was confirmed, at least in the Compton-thin regime. In contrast, NGC 1365, the only Compton-thick object in the MAXI catalog, was found to deviate from the correlation toward a significantly lower X-ray luminosity by nearly an order of magnitude. It was verified that the relation between the X-ray hardness below 10 keV and X-ray-to-infrared color acts as an effective tool to pick up Compton-thick objects. The difference in the infrared colors between the type-1 and type-2 Seyfert galaxies and its physical implication on the classification and unification of active galactic nuclei are briefly discussed.

MISC

 51
  • 井口聖, 磯部直樹, 山田亨, 大西利和, 山崎康正, 松本健, 山内大介, 土屋史紀, 高橋慶太郎, 岩田隆浩, 宇佐美尚人, 関本裕太郎, 宮崎康行, 佐伯孝尚, 森治, 吉光徹雄
    日本天文学会年会講演予稿集 2024 2024年3月  
  • Hori, T, Shidatsu, M, Ueda, Y, Kawamuro, T, Morii, M, Nakahira, S, Isobe, N, Kawai, N, Mihara, T, Matsuoka, M, Morita, T, Nakajima, M, Negoro, H, Oda, S, Sakamoto, T, Serino, M, Sugizaki, M, Tanimoto, A, Tomida, H, Tsuboi, Y, Tsunemi, H, Ueno, S, Yamaoka, K, Yamada, S, Yoshida, A, Iwakiri, W, Kawakubo, Y, Sugawara, Y, Sugita, S, Tachibana, Y, Yoshii, T
    VizieR On-line Data Catalog 2023年10月  
  • 井口聖, 自然科学研究機構国立天文台, 山田亨(JAXA 宇宙科学研究所, 大西利和, 山崎康正, 松, 本健, 山内大介, 土屋史紀, 高橋慶太郎, 磯部直樹, 岩田隆浩, 宇佐美尚人, 関本裕太郎, 宮崎康行, 佐伯孝尚, 森治, 吉光徹雄
    日本天文学会年会講演予稿集 2023 2023年9月  
  • 末松芳法, 都築俊宏, 小原直樹, 磯部直樹, 鹿島伸悟ほか, JASMINE光学系検討チーム
    日本天文学会年会講演予稿集 2023 2023年9月  
  • 磯部 直樹 (ISAS/JAXA), 永井 洋 (国立天文台), 紀 基樹 (工学院大学/国立天文台), 馬場 俊介 (鹿児 島大), 中川 貴雄 (ISAS/JAXA), 砂田 裕志, 田代 信 (埼玉大学)
    日本天文学会年会講演予稿集 2023 2023年9月  筆頭著者

講演・口頭発表等

 24

共同研究・競争的資金等の研究課題

 4