Measuring microlensing parallax via simultaneous observations from
  Chinese Space Station Telescope and Roman Telescope
  Simultaneous observations from two spatially well-separated telescopes can
lead to the measurements of the microlensing parallax parameter, an important
quantity toward the determinations of the lens mass. The separation between
Earth and Sun-Earth L2 point, $\sim0.01$ AU, is ideal for parallax measurements
of short and ultra-short ($\sim$1\,hr to 10\,days) microlensing events, which
are candidates of free-floating planet (FFP) events. In this work, we study the
potential of doing so in the context of two proposed space-based missions, the
Chinese Space Station Telescope (CSST) in a Leo orbit and the Nancy Grace Roman
Space Telescope (\emph{Roman}) at L2. We show that the joint observations of
the two can directly measure the microlensing parallax of nearly all FFP events
with timescales $t_{\rm E}\lesssim$ 10\,days as well as planetary (and stellar
binary) events that show caustic crossing features. The potential of using CSST
alone in measuring microlensing parallax is also discussed.
