Ionization cone in the X-ray binary LMC X-1

In an earlier paper, we presented the first evidence for a bow-shock nebula surrounding the X-ray binary LMC X-1 on a scale of ∼15 pc, which we argued was powered by a jet associated with an accretion disk. We now present the first evidence for an ionization cone extending from an X-ray binary, a phenomenon only seen to date in active galactic nuclei (AGNs). The ionization cone, detected in the He ii λ4686/Hβ and [O III] λ5007/ Hβ line ratio maps, aligns with the direction of the jet inferred from the bow-shock nebula. The cone has an opening angle ≈45° and radial extent ≈3.8 pc. Since the He II emission cannot be explained by the companion O star, the gas in the ionization cone must be exposed to the "naked" accretion disk, thereby allowing us to place constraints on the unobservable ionizing spectrum. The energetics of the ionization cone give unambiguous evidence for an "ultraviolet-soft X-ray" (XUV) excess in LMC X-1. Any attempt to match the hard X-ray spectrum (>1 keV) with a conventional model of the accretion disk fails to account for this XUV component. We propose two likely sources for the observed anisotropy: (1) obscuration by a dusty torus, or (2) a jet-blown hole in a surrounding envelope of circumstellar absorbing material. We discuss the implications of our discovery in the context of the mass-scaling hypothesis for accretion onto black holes and suggest avenues for future research.