Discovery of the Faint X‐Ray Pulsar AX J1820.5−1434 withASCA

Abstract

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. = 18h20m295, decl. = -14°34'24'' (equinox 2000.0; error radius 05). 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 × 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 × 1022 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.