AX J1749.1-2733 and AX J1749.2-2725 - the close pair of X-ray pulsars behind the Galactic Center: an optical identification

TL;DR

This study identifies the infrared counterparts of two faint X-ray pulsars near the Galactic Center, revealing they are likely massive stars behind the galactic bulge, and examines the unique extinction law in that region.

Contribution

First precise localization and optical identification of the pulsars' counterparts, revealing their likely nature and location behind the Galactic Center.

Findings

Counterparts are likely B0-B3 type massive stars.

Distances are estimated at 12-20 kpc.

The extinction law towards the galactic bulge differs from the standard.

Abstract

Two faint X-ray pulsars, AX J1749.2-2725 and AX J1749.1-2733, located in the direction to the Galactic Center, were studied in detail using data of INTEGRAL, XMM-Newton and Chandra observatories in X-rays, the SOFI/NTT instrument in infrared and the RTT150 telescope in optics. X-ray positions of both sources were determined with the uncertainty better than ~1 arcsec, that allowed us to identify their infrared counterparts. From the subsequent analysis of infrared and optical data we conclude that counterparts of both pulsars are likely massive stars of B0-B3 classes located behind the Galactic Center at distances of 12-20 kpc, depending on the type, probably in further parts of galactic spiral arms. In addition, we investigated the extinction law towards the galactic bulge and found that it is significantly different from standard one.