Speaker
Description
Ultraluminous X-ray sources (ULXs) can be considered for the most part an extreme version of X-ray binaries accreting at super-Eddington accretion rates. The most extreme manifestation of this process, other than their abnormally bright X-ray luminosities ($L_\mathrm{X} \gtrsim 10^{39}$ erg/s) occurs in the form of hundred-parsec nebulae of ionized gas surrounding them, offering a nearby opportunity to understand the impact of super-Eddington accretion on its environment. In particular, the presence of nebulae photo-ionized by the extreme-UV (EUV)/X-ray photon field produced in the accretion disk offers clues about the bolometric flux emanating from super-Eddington disks, which are believed to emit highly anisotropically. However, direct evidence for this remains elusive.
Here I will present Integral-Field Unit optical observations with the Multi-Unit Spectroscopic Explorer (MUSE) of the famous ULX NGC 5408 X–1, which powers a $\sim$30pc nebula bright in several high-ionization lines such as HeII $\lambda$ 4686. While the nebula was known before, it is the first time we have spatially-resolved spectral information. Moreover, the low metallicity of the galaxy together with the presence of this bright ($\sim$10$^{40}$ erg/s) ULX makes it an ideal testbed for the so-called “nebular HeII $\lambda4686$ problem”: explaining the puzzling presence of high-excitation nebular lines in metal-poor, star-forming galaxies. I will discuss how from these observables and constraints on the multi-wavelength emission from the accretion disk along the line of sight we can infer the true radiative output from this canonical ULX and how, these observations disfavour ULXs as the engines behind the high-excitation lines observed in metal-poor star-forming galaxies.
| Talk category | NOVA Network 3 |
|---|---|
| Second preference | NOVA 1 |
