Near-infrared/optical identification of five low-luminosity X-ray pulsators

Abstract

We present the identification of the most likely near-infrared (NIR)/optical counterparts of five low-luminosity X-ray pulsators (AX J1700.1−4157, AX J1740.1−2847, AX J1749.2−2725, AXJ1820.5−1434 andAXJ1832.3−0840) which have long pulse periods (>150 s). TheX-ray properties of these systems suggest that they are likely members of persistent high-mass X-ray binaries or intermediate polars (IPs). Using our Chandra observations, we detected the most likely counterparts of three sources (excluding AX J1820.5−1434 and AX J1832.3−0840) in their European Southern Observatory-New Technology Telescope (ESO-NTT) NIR observations, and a possible counterpart for AX J1820.5−1434 and AX J1832.3−0840 in the Two Micron All Sky Survey and Digitized Sky Survey observations, respectively. We also performed the X-ray timing and spectral analysis for all the sources using our XMM–Newton observations, which further helped us to constrain the nature of these systems. Our multiwavelength observations suggest thatAXJ1749.2−2725 andAXJ1820.5−1434 most likely harbour accreting neutron stars, while AX J1700.1−4157, AX J1740.1−2847 and AX J1832.3−0840 could be IPs.