2021/06/30 by SOYDUGAN, FARUK, S. Allak, A. Akyuz +15
Physics and Astronomy · #Accretion (finance) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black-body radiation #Compact star #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Light curve #Luminosity #Optics #Photon #Physics #RADIUS #Radiation #Spectral energy distribution #Spectral line #Stars #Supergiant #astro-ph.GA #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stab3693
Accepted for publication in MNRAS. 16 pages, 12 figures, 6 tables
arxiv created 2021/12/15 · openalex publication_date 2021/12/17 · arxiv updated 2021/12/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT We present the results of a temporal and spectral analysis of the transient source ULX-4 in the galaxy M51. The data used were drawn from Chandra, XMM–Newton, and Swift-XRT archives, spanning the years 2000–2019.. The X-ray flux of the source is seen to vary by two orders of magnitudes within a month but a short-term variability was not observed over the time intervals of 100–2000 s in the 0.3–10 keV energy band. We find some evidence for the existence of bi-modality feature in the flux distribution of ULX-4. We identified two optical sources as possible counterparts within an error radius of 0.′′18 at 95 \rm per cent confidence level for ULX-4 based on the archival Hubble Space Telescope (HST)/ACS and HST/WFC3 data. Blackbody fits of the spectral energy distributions (SEDs) indicate the spectral type to be B-type stars. One of these counterparts exhibits a low-amplitude optical periodicity of 264 ± 37 d in the F606W filter; if we assume this apparent periodicity is associated with the orbital motion of the donor, then it is more likely that the donor is a red supergiant satisfying the long periodicity and accretion via Roche lobe overflow. Consequently, the SED would then have to be interpreted as a superposition of emissions from a cold donor and a hot flow component, most likely from an accretion disc. If, on the other hand, the periodicity is superorbital in nature i.e. due to possible interactions of the compact object with a circumstellar disc, the donor could then be a Be/X star hosting a neutron star.