Gamma-ray emission from the Sagittarius Dwarf Spheroidal galaxy due to millisecond pulsars

Abstract

The Fermi Bubbles are giant, gamma-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 super-massive black hole. Here we show via a spatial template analysis that much of the gamma-ray emission associated to the brightest region of substructure -- the so-called cocoon -- is likely due to the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. 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 Sgr dSph has no on-going star formation, but we nevertheless demonstrate that the dwarf's millisecond pulsar (MSP) population can plausibly supply the gamma-ray signal that our analysis associates to 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 MSPs belonging to the Sgr dSph, combined with these objects' magnetospheric emission. This finding plausibly suggests that MSPs produce significant gamma-ray emission amongst old stellar populations, potentially confounding indirect dark matter searches in regions such as the Galactic Centre, the Andromeda galaxy, and other massive Milky Way dwarf spheroidals.

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

References in corpus (21)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Atlas3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies
• The Spectrum and Morphology of the Fermi Bubbles
• Tango for three: Sagittarius, LMC, and the Milky Way
• Global cosmic-ray related luminosity and energy budget of the Milky Way
• The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
• A New Model For The Loop-I (The North Polar Spur) Region
• High-Energy Gamma Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium
• The last breath of the Sagittarius dSph
• 3D Distribution of Molecular Gas in the Barred Milky Way
• Observations of M31 and M33 with the Fermi Large Area Telescope: a galactic center excess in Andromeda?
• A model-independent analysis of the Fermi Large Area Telescope gamma-ray data from the Milky Way dwarf galaxies and halo to constrain dark matter scenarios
• Millisecond Pulsars from Accretion Induced Collapse as the Origin of the Galactic Centre Gamma-ray Excess Signal
• Cosmic-ray positrons from millisecond pulsars
• The star formation history of the Sculptor dwarf spheroidal galaxy
• Local Group dSph radio survey with ATCA (II): Non-thermal diffuse emission
• Revealing the Structure and Internal Rotation of the Sagittarius Dwarf Spheroidal Galaxy with Gaia and Machine Learning
• Estimating the GeV Emission of Millisecond Pulsars in Dwarf Spheroidal Galaxies
• Evidence for a high-energy tail in the gamma-ray spectra of globular clusters

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• Investigating the effect of Milky Way dwarf spheroidal galaxies extension on dark matter searches with Fermi-LAT data
• Search for Ultraheavy Dark Matter from Observations of Dwarf Spheroidal Galaxies with VERITAS
• Dark Matter Line Searches with the Cherenkov Telescope Array
• Revisiting Primordial Black Hole Capture by Neutron Stars
• CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra). I. A predictive model for galactic non-thermal emission
• CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra). II. Population-level correlations between galactic infrared, radio, and γ-ray emission
• Gamma-Ray Millisecond Pulsars: Off-pulse Emission Characteristics, Phase-Resolved Pseudo-Luminosity--Cutoff Energy Correlation, and High-energy Pulsed Emission