Constraints on dark matter annihilation in the Large Magellanic Cloud from multiple low-frequency radio observations

Abstract

Low-frequency radio emission from the Large Magellanic Cloud (LMC) is assumed to be dominated by nonthermal synchrotron radiation from energy loss of energetic e+/e- in magnetic field. Two different kinds of sources of e+/e-, dark matter (DM) annihilation and cosmic rays (CR) related to massive stars, are taken into account in this paper. We fit the multiple low-frequency radio observations, from 19.7 MHz to 1.4 GHz, with a double power-law model Snth = SDM(ν/ν★)-αDM+SCR(ν/ν★)-αCR. ν★ is set to be 1.4 GHz. For gaugino annihilation, the flux from dark matter annihilation exhibits a ν-0.75 power-law dependence on frequency. We fix αDM and treat SCR, SDM, and αCR as free parameters when fitting the low frequency radio data. Depending on whether thermal emission is included or not, our best-fit values for SDM(ν★) range from 98.4 Jy to 114.8 Jy. Furthermore, we derive upper limits on the particle properties of dark matter associated with gaugino annihilation across various radio frequencies. Future low-frequency and high-resolution radio surveys are expected to serve as promising and powerful tools for constraining the properties of dark matter.