  The 30-year recurrent symbiotic nova V3890 Sgr exploded 2019 August 28 and
was observed with multiple X-ray telescopes. An XMM-Newton observation during
the SSS phase captured a high degree of X-ray variability including a deep dip
in the middle of the observation, an initial rise of similar depth and shape
and, after the deep dip, smaller dips of 10% amplitude, which might be periodic
over 18.1-minutes. An eclipse model of the dips yields clump sizes and orbital
radii of 0.5-8 and 5-150 white dwarf radii, respectively. The simultaneous UV
light curve shows no significant variations beyond slow fading. The RGS
spectrum contains both residual shock emission at short wavelengths and the SSS
emission at longer wavelengths. The shock temperature has clearly decreased
compared to an earlier Chandra observation (day 6). The dip spectrum is
dominated by emission lines like in U Sco. The intensity of underlying
blackbody-like emission is much lower with the blackbody normalisation yielding
a similar radius as during the brighter phases, while the lower bolometric
luminosity is ascribed to lower T_eff. This would be inconsistent with clump
occultations unless Compton scattering of the continuum emission reduces the
photon energies to mimic a lower effective temperature. However, systematic
uncertainties are high. The absorption lines in the bright SSS spectrum are
blue-shifted by 870+/-10 km/s before the dip and 900+/-10 km/s, after the dip.
The reproduction of the observed spectrum is astonishing, especially that only
a single absorbing layer is necessary while three such layers are needed to
reproduce the RGS spectrum of V2491 Cyg. The ejecta of V3890 Sgr are thus more
homogeneous than many other SSS spectra indicate. Abundance determination is in
principle possible but highly uncertain. Generally, solar abundances are found
except for N and possibly O higher by an order of magnitude.
