Synchrotron emission from neutralino dark matter annihilation in dwarf spheroidal galaxies

Abstract

The existence of non-baryonic cold dark matter has been established by several astrophysical evidences. In the regions of high dark matter density, the dark matter particles can undergo self-annihilation yielding standard model particles. Such particles may have effects on the observational properties of astronomical objects, which may then be used to constrain the nature of dark matter. High-energy electrons and positrons produced by dark matter annihilation in an astrophysical system emit synchrotron radiation due to the presence of the magnetic field. This synchrotron radiation can be detected by a radio telescope. Dwarf spheroidal galaxies of the Milky Way are some of the darkest matter-dominated objects in the Universe and thus provide natural targets for indirect dark matter searches or to constrain the synchrotron signal from the annihilation of dark matter. In this work, we study the radio emission due to neutralino dark matter emission in the nearby dwarf spheroidal galaxies – Ursa Minor, Willman I, Sculptor and Ursa Major II. Assuming the Navarro–Frenk–White (NFW) dark matter density profile within the halo of the dwarf galaxies, the upper limit of synchrotron flux is found to be ~10⁻¹⁴ ergs cm⁻² s⁻¹ for neutralino mass $M_{\chi } = 1 \,{\text{TeV}}$ annihilating into μ⁺μ⁻ state and B₀ $=$ 4 μG. For B₀ $=$ 2 μG, the flux is one order less. It is seen that as the electron energy approaches the neutralino mass, electron number density decreases. Moreover, the peak frequency is found to follow a power-law with the neutralino mass with a universal exponent.