Rapid Dimming Followed by a State Transition: A Study of the Highly Variable Nuclear Transient AT 2019avd over 1000+ Days
Journal article, 2024

The tidal disruption of a star around a supermassive black hole (SMBH) offers a unique opportunity to study accretion onto an SMBH on a human timescale. We present results from our 1000+ days monitoring campaign of AT 2019avd, a nuclear transient with tidal-disruption-event-like properties, with NICER, Swift, and Chandra. Our primary finding is that approximately 225 days following the peak of the X-ray emission, there is a rapid drop in luminosity exceeding 2 orders of magnitude. This X-ray dropoff is accompanied by X-ray spectral hardening, followed by a plateau phase of 740 days. During this phase, the spectral index decreases from 6.2 ± 1.1 to 2.3 ± 0.4, while the disk temperature remains constant. Additionally, we detect pronounced X-ray variability, with an average fractional rms amplitude of 47%, manifesting over timescales of a few dozen minutes. We propose that this phenomenon may be attributed to intervening clumpy outflows. The overall properties of AT 2019avd suggest that the accretion disk evolves from a super-Eddington to a sub-Eddington luminosity state, possibly associated with a compact jet. This evolution follows a pattern in the hardness-intensity diagram similar to that observed in stellar-mass BHs, supporting the mass invariance of accretion-ejection processes around BHs

Author

Yanan Wang

University of Southampton

Chinese Academy of Sciences

Dheeraj R. Pasham

Massachusetts Institute of Technology (MIT)

D. Altamirano

University of Southampton

Andrés Gúrpide

University of Southampton

N. Castro Segura

University of Southampton

Matthew Middleton

University of Southampton

Long Ji

Sun Yat-Sen University

Santiago Del Palacio

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Muryel Guolo

Johns Hopkins University

Poshak Gandhi

University of Southampton

Shuang Nan Zhang

Chinese Academy of Sciences

R. Remillard

Massachusetts Institute of Technology (MIT)

Dacheng Lin

Northeastern University

Megan Masterson

Massachusetts Institute of Technology (MIT)

R. D. Baldi

Istituto di Radioastronomia

University of Southampton

Francesco Tombesi

University of Maryland

INAFOsservatorio Astronomico di Roma

University of Rome Tor Vergata

NASA Goddard Space Flight Center

Jon M. Miller

University of Michigan

Wenda Zhang

Chinese Academy of Sciences

Andrea Sanna

University of Cagliari

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 962 1 78

Subject Categories

Subatomic Physics

Astronomy, Astrophysics and Cosmology

DOI

10.3847/1538-4357/ad182b

Related datasets

Chandra data sets [dataset]

DOI: 10.25574/cdc.170

More information

Latest update

2/23/2024