Total X-Ray Emission from the LMC Observed with HaloSat

Abstract

We constrain the global parameters of the Large Magellanic Cloud (LMC) by modeling the first soft X-ray (0.4–6.8 keV) observations of the entire LMC produced in a single pointing with moderate spectral resolution by the HaloSat CubeSat. These data are best fit with the sum of two thermal plasma components in collisional ionization equilibrium and a power law. We find cool (0.210 ± 0.014 keV) and hot (0.89 ± 0.14 keV) components. The total X-ray luminosity of the LMC is (1.08 ± 0.14) × 10³⁹ erg s⁻¹. X-ray binaries make up a large fraction of the emission with a luminosity of (6.0 ± 0.8) × 10³⁸ erg s⁻¹, followed by cool gas from superbubbles, supernovae, and diffuse emission with a luminosity of (3.0 ± 0.3) × 10³⁸ erg s−¹. The hot gas from star formation contributes the smallest fraction, with a luminosity of (1.9 ± 0.5) × 10³⁸ erg s⁻¹. We estimate the total volume of the cool gas to be between (0.2–1.2) × 10¹⁰ pc³ and the hot gas to be between (1.0–5) × 10⁷ pc³ for filling factors of f = 1 and 0.2. These volumes result in a total thermal energy for the cool gas between (1.4–3) × 1054 erg for electron densities of 0.017–0.04 cm⁻³, and a thermal energy for the hot gas between (1.7–4) × 10⁵³ erg for electron densities of 0.12–0.3 cm⁻³. This yields cooling timescales for the cool and hot gas of (1.5–3) × 10⁸ yr and (1.8–6) × 10⁷ yr, respectively.