Comprehensive X-ray and Multiwavelength Study of ULXs in NGC 1566

TL;DR

This study uses archival X-ray and multi-wavelength data to analyze ULXs in NGC 1566, revealing spectral state transitions, a new transient ULX, and insights into their optical/NIR counterparts and donor stars.

Contribution

It provides the first detailed multi-wavelength analysis of ULXs in NGC 1566, including the discovery of a new transient ULX and characterization of their counterparts.

Findings

ULX-3 shows spectral state transitions from hard to soft.

A new transient ULX-4 was identified with peak luminosity 10E40 erg/s.

Optical/NIR counterparts suggest a circumbinary disk for ULX-1 and ULX-2, and a B-type supergiant donor for ULX-3.

Abstract

This paper presents a comprehensive X-ray and multi-wavelength study of ultraluminous X-ray sources (ULXs) in NGC 1566 using archival Chandra, Swift/XRT, James Webb Space Telescope, JWST, and Hubble Space Telescope, HST observations. The main results are, first, from the hardness ratio diagram, where spectral state transitions from hard to soft as seen in typical Galactic high mass X-ray binaries for ULX-3 was observed. Second, a new transient ULX candidate (ULX-4) was identified, reaching a peak luminosity of 10E40 erg/s. Third, the optical and NIR (near-infrared) counterparts of the ULXs were searched from the precise astrometric calculations. For ULX-1 and ULX-2, evidence was found that the observed NIR emission is due to the circumbinary disk/dust disrupted by X-rays. Fourth, the optical observations suggest that the possible donor star of ULX-3 is a B-type supergiant. In the case of ULX-4, the multi-wavelength properties are not clear since many sources are detected within the astrometric error radius.