Gamma-ray emission from the Sagittarius dwarf spheroidal galaxy due to millisecond pulsars

Roland M. Crocker*, Oscar Macias*, Dougal Mackey, Mark R. Krumholz, Shin’ichiro Ando, Shunsaku Horiuchi, Matthew G. Baring, Chris Gordon, Thomas Venville, Alan R. Duffy, Rui Zhi Yang, Felix Aharonian, J. A. Hinton, Deheng Song, Ashley J. Ruiter, Miroslav D. Filipović

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    12 Citations (Scopus)


    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.

    Original languageEnglish
    Pages (from-to)1317-1324
    Number of pages8
    JournalNature Astronomy
    Issue number11
    Publication statusPublished - Nov 2022


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