  We report results of one-day simultaneous multiwavelength observations of
Cygnus X-2 using XMM, Chandra, the European VLBI Network and the XMM Optical
Monitor. During the observations, the source did not exhibit Z-track movement,
but remained in the vicinity of the soft apex. It was in a radio
quiescent/quiet state of < 150 microJy. Strong dip events were seen as 25%
reductions in X-ray intensity. The use of broadband CCD spectra in combination
with narrow-band grating spectra has now demonstrated for the first time that
these dipping events in Cygnus X-2 are caused by absorption in cool material in
quite a unique way. In the band 0.2 - 10 keV, dipping appears to be due to
progressive covering of the Comptonized emission of an extended accretion disk
corona, the covering factor rising to 40% in deep dipping with an associated
column density of 3.10^{23} atom cm^{-2}. Remarkably, the blackbody emission of
the neutron star is not affected by these dips, in strong contrast with
observations of typical low mass X-ray binary dipping sources. The Chandra and
XMM gratings directly measure the optical depths in absorption edges such as Ne
K, Fe L, and O K and a comparison of the optical depths in the edges of non-dip
and dip data reveals no increase of optical depth during dipping even though
the continuum emission sharply decreases. Based on these findings, at orbital
phase 0.35, we propose that dipping in this observation is caused by absorption
in the outer disk by structures located opposite to the impact bulge of the
accretion stream. With an inclination angle > 60 deg, these structures can
still cover large parts of the extended ADC, without absorbing emission from
the central neutral star.
