Abstract
ABSTRACT This paper presents the identification of a new transient ultraluminous X-ray source (ULX) candidate (ULX-3) with reaching a peak luminosity of ∼4 × 1039 erg s−1 in NGC 4254 by using archival Chandra, Swift/X-Ray Telescope, Hubble Space Telescope, and JWST observations. From precise astrometric calculations, unique optical, near-infrared, and mid-infrared counterparts were found. The spectral energy distribution (SED) and colour–magnitude diagrams of counterparts of the new ULX candidate were plotted to constrain the nature of the possible donor star. Evidence of a circumbinary disc 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 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.
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