Detecting Intracluster Gas Motion in Galaxy Clusters: Mock Astro-E2 Observations

We explore the detectability of bulk motions in the X-ray emitting intracluster medium (ICM) using a catalog of 1,836 mock Astro-E2 observations of simulated clusters of galaxies. We generate high resolution mock spectra for two observing strategies: a four-pointing mosaic and a single central pointing. Normalizing to 200 (400) photons in the iron K-alpha region for the mosaic (central) study, we fit Poisson realizations of each simulated spectrum to a velocity broadened isothermal plasma emission model. We confirm that the velocity characteristics (mean and dispersion) returned by the spectral fittings are unbiased measures of the emission-weighted values within the observed region, with scatter 55 km/s. The maximum velocity difference between mosaic element pairs $\mathrm{\Delta }{v}_{\mathrm{m}\mathrm{a}\mathrm{x}}$ has ~ 6% likelihood of being transonic ($\mathrm{\Delta }{v}_{\mathrm{m}\mathrm{a}\mathrm{x}}\ge 0.5c_s$), and the likelihood falls steeply, $p\text{spropto}(\mathrm{\Delta }{v}_{\mathrm{m}\mathrm{a}\mathrm{x}}\mathrm{/}{c}_s{)}^{-4}$, at high Mach number. The velocity broadening parameter ${\sigma }_v$ from the central pointing fit exceeds the thermal value in 49% of the cases, with again a ${\sigma }_v^{-4}$ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.