XMM-Newton observations of five INTEGRAL sources located towards the Scutum Arm

TL;DR

This study uses XMM-Newton observations to refine positions and classify five INTEGRAL sources towards the Scutum Arm, revealing neutron star pulsations, potential AGN features, and new high-mass X-ray binary candidates.

Contribution

First detailed spectral and timing analysis of five INTEGRAL sources, providing classifications and discovering pulsations and possible AGN signatures.

Findings

Discovered 997-s pulsation in IGR J18462-0223 indicating a neutron star in a HMXB.

Identified IGR J18457+0244 as a potential Sey-2 AGN with possible quasi-periodic oscillation.

Proposed new HMXB candidate IGR J18482+0049 based on spectral properties.

Abstract

Results are presented for XMM-Newton observations of five hard X-ray sources discovered by INTEGRAL in the direction of the Scutum Arm. Each source received more than 20 ks of effective exposure time. We provide refined X-ray positions for all five targets enabling us to pinpoint the most likely counterpart in optical/infrared archives. Spectral and timing information (much of which are provided for the first time) allow us to give a firm classification for IGR J18462-0223 and to offer tentative classifications for the others. For IGR J18462-0223, we discovered a coherent pulsation period of 997+-1 s which we attribute to the spin of a neutron star in a highly-obscured (nH = 2e23 /cm2) high-mass X-ray binary (HMXB). This makes IGR J18462-0223 the seventh supergiant fast X-ray transient (SFXT) candidate with a confirmed pulsation period. IGR J18457+0244 is a highly-absorbed (nH = 8e23 /cm2) source in which the possible detection of an iron line suggests an active galactic nucleus (AGN) of type Sey-2 situated at z = 0.07(1). A periodic signal at 4.4 ks could be a quasi-periodic oscillation which would make IGR J18457+0244 one of a handful of AGN in which such features have been claimed, but a slowly-rotating neutron star in an HMXB can not be ruled out. IGR J18482+0049 represents a new obscured HMXB candidate with nH = 4e23 /cm2. We tentatively propose that IGR J18532+0416 is either an AGN or a pulsar in an HMXB system. The X-ray spectral properties of IGR J18538-0102 are consistent with the AGN classification that has been proposed for this source.