A Multiwavelength Study of ULXs in NGC 1792: A New Transient ULX and Candidate Optical/NIR Counterparts

Abstract

We present a multiwavelength study of the ultraluminous X-ray (ULX) population in NGC 1792 using archival Chandra, HST, and JWST observations. We report the identification of a new ULX candidate (ULX-3), detected only during the 2016 Chandra observation, while ULX-1 and ULX-2 remain persistently detected across all available epochs. Long-term X-ray monitoring shows that ULX-1 and ULX-2 vary by factors of ∼5 and ∼3, respectively, while ULX-3 exhibits strong variability (∼70), consistent with a transient nature. X-ray spectral analysis suggests that all three sources are likely powered by super-Eddington accretion onto stellar-mass compact objects. ULX-1 alternates between hard power-law and hot disc-like emission, ULX-2 shows softer spectra with a cooler disc component, and ULX-3 is harder and more variable. These properties are compatible with either neutron-star or black-hole accretors, but the available data are insufficient to determine the nature. Optical and near-infrared counterparts are identified using HST and JWST imaging, yielding one to two candidates per source. Colour–magnitude analysis suggests young stellar environments for ULX-1 and ULX-3, while ULX-2 is consistent with an older population. Combined CMD, SED, and luminosity-radius constraints suggest that the selected donor candidates associated with these ULXs have estimated masses of ∼10 - 14 M⊙, with radii consistent with evolved massive stars. Overall, the results support a high-mass X-ray binary interpretation for all three ULXs, while the nature of the donor stars remains unconstrained with the current data and is dependent on model assumptions and limited photometric coverage.