Discovery of the faint X-ray pulsar AX J1820.5-1434 with ASCA

A new X-ray pulsar, AX J1820.5-1434, has been discovered during the ASCA Galactic plane survey project on April 9, at R.A. = 18(h)20(m)29.(s)5, decl. = -14 degrees 34'24 " (equinox 2000.0; error radius 0.'5). A coherent pulsation was detected from the source with an apparent barycentric pulse period of 152.26 +/- 0.04 s. The mean flux, not corrected for the interstellar absorption, was 2.3 x 10(-11) ergs s(-1) cm(-2) in the 2-10 keV energy band. The energy spectra obtained by the GIS and SIS can be fitted by a power-law model (photon index = 0.9 +/- 0.2) with a large column density of 9.8 +/- 1.7 x 10(22) H atoms cm(-2). These parameters indicate that the new pulsar is a highly obscured accretion-driven binary X-ray pulsar. This discovery of a faint pulsar suggests existence of many hidden pulsars in our Galaxy.