New Transient ULX Candidate in NGC 4254: Evidence of Circumbinary Disk?

Abstract

This paper presents the identification of a new transient ULX candidate (ULX-3) with reaching a peak luminosity of ~ 4e39 erg/s in NGC 4254 by using archival Chandra, Swift X-Ray Telescope (Swift/XRT), Hubble Space Telescope (HST), and James Webb Space Telescope (JWST) observations. From precise astrometric calculations, unique optical, near-infrared (NIR) and mid-infrared (mid-IR) counterparts were found. The spectral energy distribution (SED) and color-magnitude diagrams (CMDs) of counterparts of the new ULX candidate were plotted to constrain the nature of the possible donor star. Evidence of a circumbinary disk was found from its SED with two blackbody temperatures of 1000 and 200 K. Moreover, according to the X-ray hardness ratios, ULX-3 exhibits very hard to very soft transitions as seen in some high-mass X-ray binaries (HMXBs) with Be-star donors Moreover, ULX-3 varies by more than two orders of magnitude in the 0.3-10 keV energy band as seen in typical transient ULXs.