Gamma-ray emission from the Sagittarius dwarf spheroidal galaxy due to millisecond pulsars
Abstract
The Fermi bubbles are giant, γ-ray-emitting lobes emanating from the nucleus of the Milky Way discovered in ~1-100 GeV data collected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. Previous work has revealed substructure within the Fermi bubbles that has been interpreted as a signature of collimated outflows from the Galaxy's supermassive black hole. Here we show via a spatial template analysis that much of the γ-ray emission associated with the brightest region of substructure—the so-called cocoon—is probably due to the Sagittarius dwarf spheroidal galaxy (dSph). This large Milky Way satellite is viewed through the Fermi bubbles from the position of the Solar System. As a tidally and ram-pressure stripped remnant, the Sagittarius dSph has no ongoing star formation, but we nevertheless demonstrate that the dwarf's millisecond pulsar population can plausibly supply the γ-ray signal that our analysis associates with its stellar template. The measured spectrum is naturally explained by inverse Compton scattering of cosmic microwave background photons by high-energy electron-positron pairs injected by millisecond pulsars belonging to the Sagittarius dSph, combined with these objects' magnetospheric emission. This finding plausibly suggests that millisecond pulsars produce significant γ-ray emission among old stellar populations, potentially confounding indirect dark-matter searches in regions such as the Galactic Centre, the Andromeda galaxy and other massive Milky Way dSphs.
- Publication:
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Nature Astronomy
- Pub Date:
- November 2022
- DOI:
- 10.1038/s41550-022-01777-x
- arXiv:
- arXiv:2204.12054
- Bibcode:
- 2022NatAs...6.1317C
- Keywords:
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- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Updated to match version accepted for publication in Nature Astronomy (2022). 14 pages main text, 3 main figures, 7 extended data figures. For published version of the paper, see https://rdcu.be/cUZ6X