  The transient 500 s X-ray pulsar MAXI J1409-619 was discovered by the slit
cameras aboard MAXI on October 17, 2010, and soon after accurately localized by
Swift. We found that the source position was serendipitously observed in 2000
during BeppoSAX observations of the Galactic plane. Two sources are clearly
detected in the MECS: one is consistent with the position of IGR J14043-6148
and the other one with that of MAXI J1409-619. We report on the analysis of
this archival BeppoSAX/MECS observation integrated with newly analyzed
observation from ASCA and a set of high-energy observations obtained from the
offset fields of the BeppoSAX/PDS instrument. For the ON-source observation,
the 1.8-100 keV spectrum is fit by an absorbed power law with a photon index
Gamma = 0.87_{-0.19}^{+0.29}, corresponding to 2-10 and 15-100 keV unabsorbed
fluxes of 2.7E-12 and 4E-11 erg/cm2/s, respectively, and a 2-10 keV luminosity
of 7E+34 erg/s for a 15 kpc distance. For a PDS offset field observation,
performed about one year later and showing a 15-100 keV flux of 7E-11
erg/cm2/s, we clearly pinpoint three spectral absorption features at 44, 73,
and 128 keV, resolved both in the spectral fit and in the Crab ratio. We
interpret these not harmonically spaced features as due to cyclotron
resonances. The fundamental energy of 44 +/- 3 keV corresponds to a magnetic
field strength at the neutron star surface of 3.8E12 (1+z) G, where z is the
gravitational redshift. We discuss the nature of the source in the light of its
possible counterpart.
