  The hard X-ray survey that Swift-BAT has been performing since late 2004 has
provided a considerable database for a large number of sources whose hard X-ray
emission was poorly known. We are exploiting the BAT survey archive to improve
the temporal and spectral characterization of the Galactic hard-X-ray sources.
In this letter we focus on the study of the high mass X-ray binary AX
J1820.5-1434. All the data relevant to AX J1820.5-1434 have been extracted from
the BAT survey archive and analyzed using a folding technique to search for
periodical modulations. A broad-band spectral analysis was also performed
complementing the BAT spectrum with the available Swift-XRT and XMM-Newton
pointed observations. A timing analysis has revealed the detection of a
coherent signal at P_0=54.0 +/- 0.4 days, that we interpret as the orbital
period of the binary system. When folded with a period of P_0, the light curve
shows an asymmetric profile, with a minimum roughly consistent with zero
intensity. The broad band spectral analysis performed coupling Swift-XRT,
XMM-Newton and Swift-BAT spectra is well modeled with an absorbed power law
with no evidence for an exponential cutoff.
