Extreme variability in an active galactic nucleus: Gaia16aax

Understand

We present the results of a multi-wavelength follow up campaign for the luminous nuclear transient Gaia16aax, which was first identified in January 2016.

• The transient is spatially consistent with the nucleus of an active galaxy at z=0.25, hosting a black hole of mass $\rm \sim6\times10^8M_\odot$.
• The nucleus brightened by more than 1 magnitude in the Gaia G-band over a timescale of less than one year, before fading back to its pre-outburst state over the following three years.
• The optical spectra of the source show broad Balmer lines similar to the ones present in a pre-outburst spectrum.