2012/05/02 by Joel N. Bregman, Julie N. Felberg, Bregman, Joel N. +9
Decision Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Scientific Measurement and Uncertainty Evaluation #X-ray Spectroscopy and Fluorescence Analysis #astro-ph.HE
paper · pdf · doi:10.48550/arxiv.1205.0424
18 pages, 6 figures
arxiv created 2012/05/02 · openalex publication_date 2012/05/02 · arxiv updated 2012/05/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
To further understand the nature of the optical counterparts associated with Ultraluminous X-Ray sources (ULXs), we obtained far ultraviolet spectra of the reported counterparts to the ULXs in NGC 1313, Holmberg II, NGC 5204, and M81. The spectral resolution of the ACS prism spectra degrades from 300 at 1300 A to 40 at 1850 A, so longer wavelength features have lower S/N. The spectra of the ULXs in NGC 1313, Ho II, and NGC 5204 are quite similar, showing the N V 1240 A line at about the same equivalent width strength. The presence of this and other emission lines confirms the presence of an accretion disk, probably diluted by the light of an early B star companion. The spectra differ strongly from high mass X-ray binaries dominated by O star winds (e.g., Cyg X-1) and are most similar to intermediate mass X-ray binary systems in the Milky Way and LMC. This indicates that the mass transfer is due to Roche Lobe overflow. The spectrum of the ULX in M81 is quite weak but suggestive of a late-type Wolf-Rayet star.