Extreme Accretion Events: TDEs and Changing-Look AGN

Abstract

We present a review of the topics of X-ray stellar tidal disruption events (TDEs) and changing-look active galactic nuclei (AGN). Stars approaching a supermassive black hole (SMBH) can be tidally disrupted and accreted. TDEs were first discovered in the X-ray regime and appear as luminous, giant-amplitude flares from inactive galaxies. The early X-ray observations with ROSAT also established the extreme X-ray spectral softness of these events with temperatures of order 50-100 eV that continues to be seen in the majority of more recently identified events. While the majority of X-ray TDEs has been identified from {\it inactive} galaxies and some showed the highest amplitudes of variability recorded from galaxy cores (amplitudes exceeding factors of 1000--6000), a small fraction of {\it active} galactic nuclei (AGN) has been found to be highly variable as well. In AGN, this so-called changing-look phenomenon often comes with a strong change in the optical broad emission lines, leading to Seyfert-type changes between class 1 and class 2. These two forms of activity represent the extremes of variability among active and quiescent galaxies, and have opened up a new window on understanding accretion physics under extreme conditions. Finally, we introduce the term ``frozen-look AGN'' to describe systems that show constant line emission despite strong/dramatic changes in the observed ionizing continuum. These systems are best explained by strong changes of absorption along our line-of-sight.

Invited review, XMM-Newton Science Workshop 2022 on Black Hole Accretion, to appear in AN

References in corpus (22)

• An online repository of Swift/XRT light curves of GRBs
• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Evolution of tidal disruption candidates discovered by XMM-Newton
• The destruction and recreation of the X-ray corona in a changing-look Active Galactic Nucleus
• A milliparsec supermassive black hole binary candidate in the galaxy SDSS J120136.02+300305.5
• Disc tearing: implications for black hole accretion and AGN variability
• New changing look case in NGC 1566
• Discovery of the Narrow-Line Seyfert 1 galaxy Mkn 335 in an historical low X-ray flux state
• The Time Domain Spectroscopic Survey: Changing-Look Quasar Candidates from Multi-Epoch Spectroscopy in SDSS-IV
• A candidate tidal disruption event in the Galaxy cluster Abell 3571
• IC 3599 did it again: A second outburst of the X-ray transient Seyfert 1.9 Galaxy
• RBS 1032: A Tidal Disruption Event in Another Dwarf Galaxy?
• The Eccentric Nature of Eccentric Tidal Disruption Events
• XMM-Newton observation of the deep minimum state of PG 2112+059: A spectrum dominated by reflection from the accretion disk?
• Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events
• Optical and X-ray discovery of the changing-look AGN IRAS23226-3843 showing extremely broad and double-peaked Balmer profiles
• The nozzle shock in tidal disruption events
• A Library of Synthetic X-ray Spectra for Fitting Tidal Disruption Events
• Stars Crushed by Black Holes. II. A Physical Model of Adiabatic Compression and Shock Formation in Tidal Disruption Events
• Follow-up Observations of the Prolonged, super-Eddington, Tidal Disruption Event Candidate 3XMM~J150052.0+015452: the Slow Decline Continues
• Tidal Disruption Events by Compact Supermassive Black Hole Binaries

Cited by in corpus (4)

• Science objectives of the Einstein Probe mission
• The rate of extreme coronal line emitting galaxies in the Sloan Digital Sky Survey and their relation to tidal disruption events
• Clues on the nature of the quasi-periodic optical outbursts of the blazar OJ 287
• X-ray properties of two complementary samples of intermediate Seyfert galaxies