Extreme variability in an active galactic nucleus: Gaia16aax

Abstract

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 $\sim 6\times 10^8{\mathrm{M}}_{\odot }$. 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. During the outburst, the $\mathrm{H}\alpha$ and $\mathrm{H}\beta$ emission lines develop a secondary peak. We also report on the discovery of two transients with similar light curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disk. We consider variability in the accretion flow in the inner part of the disk, or a tidal disruption event of a star $\ge 1M_{\odot }$ by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria.

21 pages, 17 figure - accepted for publication in MNRAS main journal

References in corpus (19)

• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Accretion disc viscosity: how big is alpha?
• Determining the Type, Redshift, and Age of a Supernova Spectrum
• A Continuum of H- to He-Rich Tidal Disruption Candidates With a Preference for E+A Galaxies
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• Stellar disruption by a supermassive black hole: is the light curve really proportional to $t^{-5/3}$?
• The Superluminous Transient ASASSN-15lh as a Tidal Disruption Event from a Kerr Black Hole
• Quasar Accretion Disks Are Strongly Inhomogeneous
• Understanding extreme quasar optical variability with CRTS: I. Major AGN flares
• A likely decade-long sustained tidal disruption event
• A population of highly energetic transient events in the centres of active galaxies
• The Long Term Evolution of ASASSN-14li
• MUSE Reveals a Recent Merger in the Post-starburst Host Galaxy of the TDE ASASSN-14li
• The Nature of Transition Blazars
• X-ray bolometric corrections for Compton-thick active galactic nuclei
• Correcting second-order contamination in low-resolution spectra
• Magnetorotationally driven wind cycles in local disc models
• The 'Big Dipper': The nature of the extreme variability of the AGN SDSS J2232-0806