Rapid dimming followed by a state transition: a study of the highly variable nuclear transient AT 2019avd over 1000+ days
| Autor: | Wang, Yanan, Pasham, Dheeraj R., Altamirano, Diego, Gurpide, Andres, Segura, Noel Castro, Middleton, Matthew, Ji, Long, del Palacio, Santiago, Guolo, Muryel, Gandhi, Poshak, Zhang, Shuang-Nan, Remillard, Ronald, Lin, Dacheng, Masterson, Megan, Baldi, Ranieri D., Tombesi, Francesco, Miller, Jon M., Zhang, Wenda, Sanna, Andrea |
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| Rok vydání: | 2023 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | The tidal disruption of a star around a supermassive black hole (SMBH) offers a unique opportunity to study accretion onto a SMBH on a human-timescale. We present results from our 1000+ days NICER, Swift and Chandra monitoring campaign of AT 2019avd, a nuclear transient with TDE-like properties. Our primary finding is that approximately 225 days following the peak of X-ray emission, there is a rapid drop in luminosity exceeding two orders of magnitude. This X-ray drop-off is accompanied by X-ray spectral hardening, followed by a 740-day plateau phase. 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 root mean squared 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 black holes, supporting the mass invariance of accretion-ejection processes around black holes. Comment: 21 pages, 11 figures, 1 table; accepted for publication in ApJ |
| Databáze: | arXiv |
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