X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures
The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning...
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MDPI AG
2018-02-01
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| Series: | Galaxies |
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| Online Access: | http://www.mdpi.com/2075-4434/6/1/27 |
| _version_ | 1818543143878918144 |
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| author | Jun Kataoka Yoshiaki Sofue Yoshiyuki Inoue Masahiro Akita Shinya Nakashima Tomonori Totani |
| author_facet | Jun Kataoka Yoshiaki Sofue Yoshiyuki Inoue Masahiro Akita Shinya Nakashima Tomonori Totani |
| author_sort | Jun Kataoka |
| collection | DOAJ |
| description | The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π0 decay of accelerated protons or electron bremsstrahlung. |
| first_indexed | 2024-12-11T22:31:28Z |
| format | Article |
| id | doaj.art-c2986dd02c864f3b80432fdb625ff79d |
| institution | Directory Open Access Journal |
| issn | 2075-4434 |
| language | English |
| last_indexed | 2024-12-11T22:31:28Z |
| publishDate | 2018-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Galaxies |
| spelling | doaj.art-c2986dd02c864f3b80432fdb625ff79d2022-12-22T00:48:08ZengMDPI AGGalaxies2075-44342018-02-01612710.3390/galaxies6010027galaxies6010027X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I StructuresJun Kataoka0Yoshiaki Sofue1Yoshiyuki Inoue2Masahiro Akita3Shinya Nakashima4Tomonori Totani5Institute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, JapanDepartment of Astronomy, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanRIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, JapanInstitute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, JapanRIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, JapanDepartment of Astronomy, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, JapanThe Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π0 decay of accelerated protons or electron bremsstrahlung.http://www.mdpi.com/2075-4434/6/1/27Fermi bubblesNorth Polar SpurLoop IGalactic haloX-rays |
| spellingShingle | Jun Kataoka Yoshiaki Sofue Yoshiyuki Inoue Masahiro Akita Shinya Nakashima Tomonori Totani X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures Galaxies Fermi bubbles North Polar Spur Loop I Galactic halo X-rays |
| title | X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures |
| title_full | X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures |
| title_fullStr | X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures |
| title_full_unstemmed | X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures |
| title_short | X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures |
| title_sort | x ray and gamma ray observations of the fermi bubbles and nps loop i structures |
| topic | Fermi bubbles North Polar Spur Loop I Galactic halo X-rays |
| url | http://www.mdpi.com/2075-4434/6/1/27 |
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