Subrelativistic Outflow and Hours-timescale Large-amplitude X-Ray Dips during Super-Eddington Accretion onto a Low-mass Massive Black Hole in the Tidal Disruption Event AT2022lri

Creators: Yao, Yuhan^{1, 2}; Guolo, Muryel³; Tombesi, Francesco^{4, 5, 6}; Li, Ruancun⁷; Gezari, Suvi^{3, 8}; García, Javier A.⁹; Dai, Lixin¹⁰; Chornock, Ryan²; Lu, Wenbin²; Kulkarni, S. R.¹¹; Gendreau, Keith C.⁹; Pasham, Dheeraj R.¹²; Cenko, S. Bradley^{9, 13}; Kara, Erin¹²; Margutti, Raffaella²; Ajay, Yukta³; Wevers, Thomas⁸; Kwan, Tom M.¹⁰; Andreoni, Igor^{9, 13}; Bloom, Joshua S.^{2, 14}; Drake, Andrew J.¹¹; Graham, Matthew J.¹¹; Hammerstein, Erica¹³; Laher, Russ R.¹⁵; LeBaron, Natalie²; Mahabal, Ashish A.¹¹; O'Connor, Brendan¹⁶; Purdum, Josiah¹¹; Ravi, Vikram¹¹; Sears, Huei¹⁷; Sharma, Yashvi¹¹; Smith, Roger¹¹; Sollerman, Jesper¹⁸; Somalwar, Jean J.¹¹; Wold, Avery¹⁵

1. New York State Office for People With Developmental Disabilities
2. University of California, Berkeley
3. Johns Hopkins University
4. University of Rome Tor Vergata
5. INAF—Astronomical Observatory of Rome, Via Frascati 33, 00040 Monte Porzio Catone, Italy
6. National Institute for Nuclear Physics
7. Peking University
8. Space Telescope Science Institute
9. Goddard Space Flight Center
10. University of Hong Kong
11. California Institute of Technology
12. Massachusetts Institute of Technology
13. University of Maryland, College Park
14. Lawrence Berkeley National Laboratory
15. Infrared Processing and Analysis Center
16. Carnegie Mellon University
17. Northwestern University
18. Stockholm University

Abstract

We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with a low-mass massive black hole (10⁴M_⊙ < M_BH < 10⁶M_⊙). AT2022lri belongs to the TDE-H+He subtype. More than 1 Ms of X-ray data were collected with NICER, Swift, and XMM-Newton from 187 to 672 days after peak. The X-ray luminosity gradually declined from 1.5 × 10⁴⁴ erg s⁻¹ to 1.5 × 10⁴³ erg s⁻¹ and remains much above the UV and optical luminosity, consistent with a super-Eddington accretion flow viewed face-on. Sporadic strong X-ray dips atop a long-term decline are observed, with a variability timescale of ≈0.5 hr–1 days and amplitude of ≈2–8. When fitted with simple continuum models, the X-ray spectrum is dominated by a thermal disk component with inner temperature going from ∼146 to ∼86 eV. However, there are residual features that peak around 1 keV, which, in some cases, cannot be reproduced by a single broad emission line. We analyzed a subset of time-resolved spectra with two physically motivated models describing a scenario either where ionized absorbers contribute extra absorption and emission lines or where disk reflection plays an important role. Both models provide good and statistically comparable fits, show that the X-ray dips are correlated with drops in the inner disk temperature, and require the existence of subrelativistic (0.1–0.3c) ionized outflows. We propose that the disk temperature fluctuation stems from episodic drops of the mass accretion rate triggered by magnetic instabilities or/and wobbling of the inner accretion disk along the black hole's spin axis.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank Norbert Schartel for approving our XMM-Newton ToO requests. We thank Andrew Mummery, Chris Nixon, Nick Stone, Anil Seth, Luis C. Ho, Hua Feng, Peter Kosec, and Junjie Mao for helpful discussions.

Y.Y. and S.R.K. acknowledge support from NASA under award Nos. 80NSSC22K1347 and 80NSSC24K0534. M.G. and S.G. are supported in part by NASA XMM-Newton grants 80NSS23K06215 and 80NSSC22K0571. F.T. acknowledges funding from the European Union—Next Generation EU, PRIN/MUR 2022 (2022K9N5B4). R.L. was supported by the National Science Foundation of China (11721303, 11991052, 12011540375, 12233001), the National Key R&D Program of China (2022YFF0503401), and the China Manned Space Project (CMS-CSST-2021-A04, CMS-CSST-2021-A06). L.D. and T.K. acknowledge support from the National Natural Science Foundation of China and the Hong Kong Research Grants Council (12122309, 17305920, 17314822, 27305119). This research was supported in part by grant No. NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP).

This work is based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, IN2P3, University of Warwick, Ruhr University Bochum, Cornell University, and Northwestern University. Operations are conducted by COO, IPAC, and UW.

SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171.

The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant No. 12540303 (PI: Graham).

This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory, led by Brad Holden, was made possible through generous gifts from the Heising-Simons Foundation, William and Marina Kast, and the University of California Observatories. Research at Lick Observatory is partially supported by a generous gift from Google.

Software References

astropy (Astropy Collaboration et al. 2013), emcee (D. Foreman-Mackey et al. 2013), GALFITS (R. Li & L. C. Ho 2024, in preparation), heasoft (NASA High Energy Astrophysics Science Archive Research Center (Heasarc) 2014), LPipe (D. A. Perley 2019), matplotlib (J. D. Hunter 2007), SAS (C. Gabriel et al. 2004), scipy (P. Virtanen et al. 2020), xspec (K. A. Arnaud 1996).

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