  We report the discovery of the new dipping X-ray source, XMMU
J004308.6+411247, in M31, during a systematic search for periodicities in
XMM-Newton archival observations. During the 2002 January 6 observation, the
dips recur with a 107 min period and the source count rate is consistent with
zero at the dip minimum. Dips with the same modulation and period are also
observed during the XMM-Newton observations carried out on 2000 June 25, 2001
June 29 and the Chandra observation of 2001 October 5. The dips of XMMU
J004308.6+411247 show no evidence of energy dependence. The average X-ray flux
of XMMU J004308.6+411247 is nearly constant across different observations
(~1.e37 erg/s for an assumed M31 distance of 780 kpc in the 0.3-10 keV band);
the spectrum is well fit by an absorbed power law with a photon index ~0.8 or
an absorbed Comptonization model. The photo-electric absorption is consistent
with the Galactic value in the source direction. If XMMU J004308.6+411247 is
located in M31 its properties are consistent with those of dipping low mass
X-ray binaries in the Galaxy. Present observations do not allow to distinguish
between dips and eclipses. The possibility that XMMU J004308.6+411247 is a
foreground X-ray source cannot be ruled out at present; in this case the source
might be a magnetic cataclysmic variable.
