Ultraviolet Spectra of ULX Systems
Abstract
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 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 most similar to intermediate mass black hole systems in the Milky Way and LMC. The weak spectrum of the ULX in M81 is suggestive of a late-type Wolf-Rayet star. We gratefully acknowledge support from NASA grant NNX10AH83G.
- Publication:
-
American Astronomical Society Meeting Abstracts #219
- Pub Date:
- January 2012
- Bibcode:
- 2012AAS...21915318F