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Detection of Nonthermal Hard X-Ray Emission from the 'Fermi Bubble' in an External Galaxy
- Source :
- Astrophys.J., Astrophys.J., 2019, 873 (1), pp.27. ⟨10.3847/1538-4357/ab010a⟩
- Publication Year :
- 2019
- Publisher :
- HAL CCSD, 2019.
-
Abstract
- We report new Chandra hard X-ray ($>2\rm~keV$) and JVLA C-band observations of the nuclear superbubble of NGC 3079, an analog of the "Fermi bubble" in our Milky Way. We detect extended hard X-ray emission on the SW side of the galactic nucleus with coherent multi-wavelength features in radio, H$\alpha$, and soft X-ray. The hard X-ray feature has a cone shape with possibly a weak cap, forming a bubble-like structure with a diameter of $\sim1.1\rm~kpc$. A similar extended feature, however, is not detected on the NE side, which is brighter in all other wavelengths such as radio, H$\alpha$, and soft X-ray. Scattered photons from the nuclear region or other nearby point-like X-ray bright sources, inverse Compton emission from cosmic ray electrons via interaction with the cosmic microwave background, or any individually faint stellar X-ray source populations, cannot explain the extended hard X-ray emission on the SW side and the strongly NE/SW asymmetry. A synchrotron emission model, plus a thermal component accounting for the excess at $\sim1\rm~keV$, can well characterize the broadband radio/hard X-ray spectra. The broadband synchrotron spectra do not show any significant cutoff, and even possibly slightly flatten at higher energy. This rules out a loss-limited scenario in the acceleration of the cosmic ray electrons in or around this superbubble. As the first detection of kpc-scale extended hard X-ray emission associated with a galactic nuclear superbubble, the spatial and spectral properties of the multi-wavelength emissions indicate that the cosmic ray leptons responsible for the broad-band synchrotron emission from the SW bubble must be accelerated in situ, instead of transported from the nuclear region of the galaxy.<br />Comment: 7 pages, 3 figures, ApJ in press
- Subjects :
- 010504 meteorology & atmospheric sciences
Milky Way
Astrophysics::High Energy Astrophysical Phenomena
Cosmic microwave background
galaxies: active
FOS: Physical sciences
Cosmic ray
Superbubble
galaxies: starburst
Astrophysics
Astrophysics::Cosmology and Extragalactic Astrophysics
01 natural sciences
Spectral line
law.invention
cosmic rays
law
0103 physical sciences
010303 astronomy & astrophysics
Astrophysics::Galaxy Astrophysics
0105 earth and related environmental sciences
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics
radio continuum: galaxies
Astronomy and Astrophysics
Astrophysics - Astrophysics of Galaxies
Synchrotron
Galaxy
X-rays: galaxies
Space and Planetary Science
Astrophysics of Galaxies (astro-ph.GA)
Astrophysics - High Energy Astrophysical Phenomena
ISM: bubbles
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Fermi Gamma-ray Space Telescope
Subjects
Details
- Language :
- English
- Database :
- OpenAIRE
- Journal :
- Astrophys.J., Astrophys.J., 2019, 873 (1), pp.27. ⟨10.3847/1538-4357/ab010a⟩
- Accession number :
- edsair.doi.dedup.....ab49cf72fb6db8de45eb5e7b4c3bd33e