X-ray and Gamma-ray Observations of the Fermi Bubbles and NPS/Loop I Structures

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 deg 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_solar) 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 pi^0 decay of accelerated protons or electron bremsstrahlung.

arXiv comment21 pages, 13 figures, invited review for the special issue of Galaxies, MDPI

References in corpus (68)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• The Demography of Massive Dark Objects in Galaxy Centres
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Production and propagation of cosmic-ray positrons and electrons
• Quasars, their host galaxies, and their central black holes
• A Three-Dimensional Map of Milky-Way Dust
• The Spectrum and Morphology of the Fermi Bubbles
• An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
• The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze
• On Black Hole Masses and Radio Loudness in AGN
• Study of the X-Ray Background Spectrum and its Large-Scale Fluctuation with ASCA
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• The Structure of the Milky Way's Hot Gas Halo
• Extended Anomalous Foreground Emission in the WMAP 3-Year Data
• Giant Magnetized Outflows from the Centre of the Milky Way
• The Fermi Bubbles. I. Possible Evidence for Recent AGN Jet Activity in the Galaxy
• A Chandra X-ray Survey of Ejecta in the Cassiopeia A Supernova Remnant
• Energy Spectra of the Soft X-ray Diffuse Emission in Fourteen Fields Observed with Suzaku
• X-ray Emission from the Hot ISM and SW Radio Lobe of the Nearby Radio Galaxy Centaurus A
• Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*
• The Fermi Bubbles: Supersonic AGN Jets with Anisotropic Cosmic Ray Diffusion
• High-energy particle acceleration at the radio-lobe shock of Centaurus A
• A New Model For The Loop-I (The North Polar Spur) Region
• Fermi gamma-ray `bubbles' from stochastic acceleration of electrons
• A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center's Giant Outflows
• Suzaku observations of the diffuse x-ray emission across the fermi bubbles' edges
• An XMM-Newton Survey of the Soft X-ray Background. III. The Galactic Halo X-ray Emission
• Probing the Fermi Bubbles in Ultraviolet Absorption: A Spectroscopic Signature of the Milky Way's Biconical Nuclear Outflow
• Chandra Observation of the Edge-on Spiral NGC 5775: Probing the Hot Galactic Disk/Halo Connection
• Planck 2015 results. XXV. Diffuse low-frequency Galactic foregrounds
• Bipolar-Hyper-Shell Galactic Center Statrburst Model: Further Evidence from ROSAT Data and New Radio and X-ray Simulations
• A RIAF Interpretation for the Past Higher Activity of the Galactic Center Black Hole and the 511 keV Annihilation Emission
• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial Extent of the Northern Fermi Bubble
• A High-Resolution X-Ray and Optical Study of SN 1006: Asymmetric Expansion and Small-Scale Structure in a Type Ia Supernova Remnant
• The Fermi Bubbles. II. The Potential Roles of Viscosity and Cosmic Ray Diffusion in Jet Models
• The Fermi Bubbles as Starburst Wind Termination Shocks
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
• The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations
• Multi-wavelength features of Fermi Bubbles as signatures of a Galactic wind
• Discovery of the recombining plasma in the south of the Galactic center; a relic of the past Galactic center activity?
• Discovery of GeV Emission from the Circinus galaxy with the Fermi-LAT
• Local ISM 3D distribution and soft X-ray background: Inferences on nearby hot gas and the North Polar Spur
• Giant Explosion at the Galactic Center and Huge Shocked Shells in the Halo
• Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement
• Radio spectral properties and the magnetic field of the SNR S147
• Evidence of Fermi bubbles around M31
• X-ray Halo Around the Spiral Galaxy NGC 4631 Observed with Suzaku
• The Fermi Bubbles as a Scaled-up Version of Supernova Remnants
• Diffuse X-Ray Sky in the Galactic Center
• The North Polar Spur and Aquila Rift
• Clues to the origin of Fermi Bubbles from OVIII/OVII line ratio
• On the distance to the North Polar Spur and the local CO-H2 factor
• A Hadronic-Leptonic Model for the Fermi Bubbles: Cosmic-Rays in the Galactic Halo and Radio Emission
• High Resolution X-ray Spectroscopy of the Local Hot Gas along the 3C 273 Sightline
• Polarization observations of SNR G156.2+5.7 at lambda 6cm
• XMM-Newton and Suzaku X-ray Shadowing Measurements of the Solar Wind Charge Exchange, Local Bubble, and Galactic Halo Emission
• Galactic-Center Hyper-Shell Model for the North Polar Spurs
• Suzaku X-ray Observations of the Fermi Bubbles: Northernmost Cap and Southeast Claw Discovered with MAXI-SSC
• Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines
• The dynamics and environmental impact of 3C452
• Galactic Center Shells and a Recurrent Starburst Model
• Interaction of the Loop I Supershell with the Local Hot Bubble
• Metal Enrichment in the Fermi Bubbles as a Probe of Their Origin
• The AGN Jet Model of the Fermi Bubbles

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• Detection of large-scale X-ray bubbles in the Milky Way halo
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• Fermi and eRosita bubbles as relics of the past activity of the Galactic black hole
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• The hot circumgalactic medium of the Milky Way: evidence for super-virial, virial, and sub-virial temperature, non-solar chemical composition, and non-thermal line broadening
• Simulating the Fermi Bubbles as Forward Shocks Driven by AGN Jets
• Revisiting the distance to radio Loops I and IV using Gaia and radio/optical polarization data
• On the Comparison of AGN with GRMHD Simulations: I. Sgr A*
• Thermal and chemical properties of the eROSITA bubbles from Suzaku observations
• A Unified Model for the Fan Region and the North Polar Spur: A bundle of filaments in the Local Galaxy
• Three-Dimensional Structure of the Central Molecular Zone
• Interaction of the Galactic-Centre Super Bubbles with the Gaseous Disc
• Origin of Galactic Spurs: New Insight from Radio/X-ray All-sky Maps
• The Central 300 pc of the Galaxy probed by infrared spectra of H3+ and CO: II. Expansion and morphology of the warm diffuse gas
• Galactic Centre Threads as Nuclear MHD Waves
• Diffuse x-ray emission from the northern arc of loop I observed with suzaku
• Diagnostics of Gaseous Halo of the Milky Way by a Shock Wave from the Galactic Centre
• North Polar Spur: gaseous plume(s) from star-forming regions at $\sim$3-5 kpc from Galactic Center?
• Cosmic rays escaping from Galactic starburst-driven superbubbles
• The Bending Feature of the Fermi Bubbles: A Presumed Horizontal Galactic Wind and Its Implication on the Bubbles' Age
• eROSITA narrowband maps at the energies of soft X-ray emission lines
• Supernova-remnant origin of the Galactic-Centre filaments
• Probing the Halo Gas Distribution in the Inner Galaxy with Fermi Bubble Observations
• Discovery of non-equilibrium ionization plasma associated with the North Polar Spur and Loop I
• Signatures of Recent Cosmic-Ray Acceleration in the High-Latitude $\gamma$-Ray Sky
• Feedback between Sgr A and B : AGN-Starburst Connection in the Galactic Centre
• Galactic Centre as an efficient source of cosmic rays
• One-kpc Expanding Cylinder of HI-Gas around the Galactic Center
• On the Hα faintness of the North Polar Spur
• Investigating the mysterious nature of 1LHAASO J1740+0948u through deep XMM-Newton observations
• Diffuse Hot Plasma in the Interstellar Medium and Galactic Outflows
• Diffuse continuum emission and large extended sources at MeV energies
• Machine learning application to Fermi-LAT data: sharpening all-sky map and emphasizing variable sources