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, AX J1820.5-1434 and AX J1832.3-0840) which have long pulse periods (>150 s). The X-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 that AX J1749.2-2725 and AX J1820.5-1434 most likely harbour accreting neutron stars, while AX J1700.1-4157, AX J1740.1-2847 and AX J1832.3-0840 could be IPs