The Hydrostatic Mass of A478: Differing Results From Chandra, NuSTAR, and XMM-Newton

Galaxy clusters are the most recently formed and most massive, gravitationally bound structures in the universe. The number of galaxy clusters formed is highly dependent on cosmological parameters, such as the dark matter density, σ₈, and Ω_m. The number per volume is a function of the cluster mass, which can be estimated from the density and temperature profiles of the intracluster medium (ICM) under the assumption of hydrostatic equilibrium. The X-ray spectra are ideal for measuring temperature; however, different X-ray telescopes report different temperatures for the same clusters, resulting in the masses differing by ~10%. This is suspected to be a calibration issue. NuSTAR is potentially less susceptible to calibration issues than Chandra and XMM-Newton, having greater sensitivity at higher energies, where the effective area is relatively constant and the exponential turnover of the continuum is more prominent. We present analyses of Chandra, NuSTAR, and XMM-Newton data of Abell 478 to investigate the nature of this calibration discrepancy. We find that the NuSTAR temperatures are on average ~10% cooler than Chandra temperatures, and XMM-Newton temperatures are on average ~5% cooler than the NuSTAR temperatures. This results in the NuSTAR mass at r₂₅₀₀ being ~10% lower than the Chandra mass at r₂₅₀₀, as expected, and the XMM-Newton mass at r₂₅₀₀ being ~2% lower than the NuSTAR mass at r₂₅₀₀.