A major prediction of most super-Eddington accretion theories is the presence of highly anisotropic emission resulting from the wind/funnel structure formed due to the intense radiation pressure in supercritical discs. Understanding the exact emission pattern of such flows has strong implications on how super-Eddington accreting sources will affect their environments. A key breakthrough allowing to test such predictions was the discovery of high-excitation photoionized nebula around Ultraluminous X-ray sources (ULXs). In such circumstances one can study the emission lines from high-excitation nebulae to assess whether the nebula ‘sees’ the same SED as observed along the line of sight. In this talk, I will present our efforts to tackle the degree of anisotropy of the emission in ULXs, coupling multi-band spectroscopy of the source with Integral-Field Unit spectroscopy of the nebular emission. I will present our recent results on the emission of the famous ULX NGC 1313 X-1, where we find that in order to reproduce the lines in the surrounding nebula, the photoionizing SED must be a factor ∼ 4 dimmer in ultraviolet emission than the line-of-sight SED. I will discuss the implications of these results in the context of ULXs and present ongoing work on another ULX with similar properties. I will finalise with some thoughts on what improvements in instrumentation and methods are needed to reduce existing uncertainties and explore the degree of anisotropy at higher energies.
27/02/2024
Colloquium Osservatorio Astronomico di Roma - Aula Gratton Tuesday 27 FEBRUARY - 11:30 (CET)
Speaker: Andres Gurpide (University of Southampton)
The seminar will be also given remotely using Google Meet at the following link: meet.google.com/zev-pdvv-gku