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 78Subject Categories
Subatomic Physics
Astronomy, Astrophysics and Cosmology
DOI
10.3847/1538-4357/ad182b
Related datasets
Chandra data sets [dataset]
DOI: 10.25574/cdc.170