Abstract
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 associationwith theNPS 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.
| Original language | English |
|---|---|
| Article number | 27 |
| Journal | Galaxies |
| Volume | 6 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 2018 Feb 26 |
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Keywords
- Fermi bubbles
- Galactic halo
- Loop I
- North Polar Spur
- X-rays
ASJC Scopus subject areas
- Astronomy and Astrophysics
Cite this
X-ray and gamma-ray observations of the fermi bubbles and NPS/Loop I structures. / Kataoka, Jun; Sofue, Yoshiaki; Inoue, Yoshiyuki; Akita, Masahiro; Nakashima, Shinya; Totani, Tomonori.
In: Galaxies, Vol. 6, No. 1, 27, 26.02.2018.Research output: Contribution to journal › Review article
}
TY - JOUR
T1 - X-ray and gamma-ray observations of the fermi bubbles and NPS/Loop I structures
AU - Kataoka, Jun
AU - Sofue, Yoshiaki
AU - Inoue, Yoshiyuki
AU - Akita, Masahiro
AU - Nakashima, Shinya
AU - Totani, Tomonori
PY - 2018/2/26
Y1 - 2018/2/26
N2 - 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 associationwith theNPS 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.
AB - 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 associationwith theNPS 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.
KW - Fermi bubbles
KW - Galactic halo
KW - Loop I
KW - North Polar Spur
KW - X-rays
UR - http://www.scopus.com/inward/record.url?scp=85043391655&partnerID=8YFLogxK
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U2 - 10.3390/galaxies6010027
DO - 10.3390/galaxies6010027
M3 - Review article
VL - 6
JO - Galaxies
JF - Galaxies
SN - 2075-4434
IS - 1
M1 - 27
ER -