There is compelling evidence for a highly energetic Seyfert explosion ( 10 ^ { 56 - 57 } erg ) that occurred in the Galactic Centre a few million years ago .
The clearest indications are the x-ray/ \gamma -ray ‘ 10 kpc bubbles ’ identified by the Rosat and Fermi satellites .
In an earlier paper , we suggested another manifestation of this nuclear activity , i.e .
elevated H \alpha emission along a section of the Magellanic Stream due to a burst ( or flare ) of ionizing radiation from Sgr A* .
We now provide further evidence for a powerful flare event : UV absorption line ratios ( in particular { C\ > \scriptstyle IV } / { C\ > \scriptstyle II } , { Si\ > \scriptstyle IV } / { Si\ > \scriptstyle II } ) observed by the Hubble Space Telescope reveal that some Stream clouds towards both galactic poles are highly ionized by a source capable of producing ionization energies up to at least 50 eV .
We show how these are clouds caught in a beam of bipolar , radiative ‘ ionization cones ’ from a Seyfert nucleus associated with Sgr A* .
In our model , the biconic axis is tilted by about 15 ^ { \circ } from the South Galactic Pole with an opening angle of roughly 60 ^ { \circ } .
For the Stream at such large Galactic distances ( D \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 75 kpc ) , nuclear activity is a plausible explanation for all of the observed signatures : elevated H \alpha emission and H ionization fraction ( x _ { e } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 0.5 ) , enhanced { C\ > \scriptstyle IV } / { C\ > \scriptstyle II } and { Si\ > \scriptstyle IV } / { Si\ > \scriptstyle II } ratios , and high { C\ > \scriptstyle IV } and { Si\ > \scriptstyle IV } column densities .
Wind-driven ‘ shock cones ’ are ruled out because the Fermi bubbles lose their momentum and energy to the Galactic corona long before reaching the Stream .
Our time-dependent Galactic ionization model ( stellar populations , hot coronal gas , cloud-halo interaction ) is too weak to explain the Stream ’ s ionization .
Instead , the nuclear flare event must have had a radiative UV luminosity close to the Eddington limit ( f _ { E } \approx 0.1 - 1 ) .
Our time-dependent Seyfert flare models adequately explain the observations and indicate the Seyfert flare event took place T _ { o } = 3.5 \pm 1 Myr ago .
The timing estimates are consistent with the mechanical timescales needed to explain the x-ray/ \gamma -ray bubbles in leptonic jet/wind models ( \approx 2 - 8 Myr ) .