Optical Polarization Reveals a Quenched Core in GSN 069
A new three-dimensional analysis conducted with the Very Large Telescope (VLT) has delved deeper into the mysteries of GSN 069, the galaxy where quasi-periodic X-ray eruptions (QPEs) were first detected. The research focuses on deciphering the origin of the past nuclear activity that shaped this cosmic system. 🔭
A Polarization Gradient that Betrays the Past
Optical polarimetry measurements have delivered a key finding: polarization increases radially, starting from values close to 0% in the core to reaching approximately 1.5% in more outer regions. This pattern is not an effect of the interstellar medium but is intrinsic to the galaxy's central engine. The gradient acts as a clear signature of a core that is no longer active, because light scattered in distant structures takes longer to reach us than light traveling directly.
Key Evidence from the Study:- The radial increase in polarization confirms the existence of an extended emission line region that had been previously detected.
- The geometry and light travel time indicate that we are observing echoes of activity that has already ceased.
- These data rule out that the pattern is caused by local or instrumental phenomena.
The polarization gradient is the luminous echo of a central engine that has shut down. The scattered light tells a story that the direct light can no longer reveal.
The Geometry of the Gas Traces a Relict Structure
The orientation of the polarization angle aligns precisely with the elongated distribution of ionized gas, observable through emission lines such as [OIII], [NII], and H-alpha. This geometric correlation suggests that the extended emission region has the shape of relict polarization cones. Such structures are usually associated with the historical presence of a dust and gas torus around the central supermassive black hole.
Implications of this Geometry:- It reinforces the idea that GSN 069 hosted an active galactic nucleus (AGN) in the past, which has now faded.
- It makes less likely, though does not entirely rule out, the hypothesis that the previous activity was primarily driven by tidal disruption events.
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