1. Introduction  
2. Observations and Data Reduction  
2.1. Narrow-band Imaging  
2.2. MUSE Spectroscopy  
2.3. UV  
2.4. Visible  
3. Analysis  
3.1. Narrow-band Imaging  
3.2. Spectroscopy  
3.3. Comparison with Other Bands  
4. Discussion  
4.1. The Source of Ionisation  
4.2. The Origin of the Filament  
5. Conclusions