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http://hdl.handle.net/20.500.12386/35588
Title: | Rapid Dimming Followed by a State Transition: A Study of the Highly Variable Nuclear Transient AT 2019avd over 1000+ Days | Authors: | Wang, Yanan Pasham, Dheeraj R. Altamirano, Diego Gúrpide, Andrés Castro Segura, Noel Middleton, Matthew Ji, Long del Palacio, Santiago Guolo, Muryel Gandhi, Poshak Zhang, Shuang-Nan Remillard, Ronald Lin, Dacheng Masterson, Megan BALDI, Ranieri Diego TOMBESI, Francesco Miller, Jon M. Zhang, Wenda SANNA, ANDREA |
Issue Date: | 2024 | Journal: | THE ASTROPHYSICAL JOURNAL | Number: | 962 | Issue: | 1 | First Page: | 78 | Abstract: | 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. | URI: | http://hdl.handle.net/20.500.12386/35588 | URL: | https://iopscience.iop.org/article/10.3847/1538-4357/ad182b https://api.elsevier.com/content/abstract/scopus_id/85184907137 |
ISSN: | 0004-637X | DOI: | 10.3847/1538-4357/ad182b | Bibcode ADS: | 2024ApJ...962...78W | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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Wang_2024_ApJ_962_78.pdf | PDF editoriale | 1.27 MB | Adobe PDF | View/Open |
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