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Title: Suzaku observations of the diffuse X-ray emission across the Fermi bubbles' edges

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 asmore » 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 {sub exp} ∼ 300 km s{sup –1} (corresponding to shock Mach number M≃1.5), 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.« less
Authors:
; ; ;  [1] ; ;  [2] ; ; ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan)
  2. Department of Astronomy, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)
  3. Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
  4. Department of Earth and Space Science, Osaka University, Osaka 560-0043 (Japan)
  5. Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
  6. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States)
  7. Department of Physics, Faculty of Science, Yamagata University, Yamagata 990-8560 (Japan)
Publication Date:
OSTI Identifier:
22348527
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COSMIC PHOTONS; EMISSION; EQUILIBRIUM; EXPANSION; GALAXIES; KEV RANGE; MACH NUMBER; PLASMA; SPECTRA; SUPERNOVA REMNANTS; X RADIATION