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First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6

Sazonov, S. and Gilfanov, M. and Medvedev, P. and Yao, Y. and Khorunzhev, G. and Semena, A. and Sunyaev, R. and Burenin, R. and Lyapin, A. and Meshcheryakov, A. and Uskov, G. and Zaznobin, I. and Postnov, K. A. and Dodin, A. V. and Belinski, A. A. and Cherepashchuk, A. M. and Eselevich, M. and Dodonov, S. N. and Grokhovskaya, A. A. and Kotov, S. S. and Bikmaev, I. F. and Zhuchkov, R. Ya and Gumerov, R. I. and van Velzen, S. and Kulkarni, S. (2021) First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6. Monthly Notices of the Royal Astronomical Society, 508 (3). pp. 3820-3847. ISSN 0035-8711. doi:10.1093/mnras/stab2843.

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We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×10³ to 10⁸M⊙⁠, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with L_g/L_X < 0.3 (L_g and L_X being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10⁻⁵ TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gilfanov, M.0000-0003-4029-6769
Medvedev, P.0000-0002-9380-8708
Yao, Y.0000-0001-6747-8509
Sunyaev, R.0000-0002-2764-7192
Postnov, K. A.0000-0002-1705-617X
Dodin, A. V.0000-0002-6755-2120
van Velzen, S.0000-0002-3859-8074
Kulkarni, S.0000-0001-5390-8563
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 September 27. Received 2021 September 11; in original form 2021 August 5. Published: 05 October 2021. This work is based on observations with the eROSITA telescope on board the SRG observatory. The SRG observatory was built by Roskosmos in the interests of the Russian Academy of Sciences represented by its Space Research Institute (IKI) in the framework of the Russian Federal Space Program, with the participation of the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The SRG/eROSITA X-ray telescope was built by a consortium of German Institutes led by the Max Planck Institute for Extraterrestrial Physics (MPE), and supported by DLR. The SRG spacecraft was designed, built, launched, and is operated by the Lavochkin Association and its subcontractors. The science data are downlinked via the Deep Space Network Antennae in Bear Lakes, Ussurijsk, and Baykonur, funded by Roskosmos. The eROSITA data used in this work were processed using the ESASS software system developed by the German eROSITA consortium and proprietary data reduction and analysis software developed by the Russian eROSITA Consortium. The observations at the 6-m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences, were carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation (including agreement No. 05.619.21.0016, project ID RFMEFI61919X0016). The observations at the AZT-33IK telescope were performed within the basic financing of the FNI II.16 program, using the equipment of the Angara sharing centre.5 Observations at the Caucasus Mountain Observatory of the Stenberg Astronomical Institute are supported by the M.V. Lomonosov Moscow State University Program of Development. The authors are grateful to TÜBITAK National Observatory, IKI, the Kazan Federal University, and the Academy of Sciences of Tatarstan for their partial support in using the Russian–Turkish 1.5-m telescope (RTT150) in Antalya. SS, MG, PM, RB, AM, and GH acknowledge the support of this research by grant 21-12-00343 from the Russian Science Foundation. YY thanks the Heising-Simons Foundation for financial support. The work of KAP and AVD is supported by the Ministry of Science and Higher Education of the Russian Federation under contract 075-15-2020-778 (observations of objects with extreme energy release) in the framework of the Large scientific projects program within the national project ‘Science’. The work of AAB and AMCh was supported by the Scientific and Educational School of M.V. Lomonosov Moscow State University ‘Fundamental and applied space research’. The work of IFB and RIG was supported by subsidy 0671-2020 0052 allocated to the Kazan Federal University for state assignment in the sphere of scientific activities. Data Availability: X-ray data analysed in this article were used by permission of the Russian SRG/eROSITA consortium. The data will become publicly available as part of the corresponding SRG/eROSITA data release along with the appropriate calibration information. Optical data used in the article will be shared on reasonable request to the corresponding author.
Group:Astronomy Department
Funding AgencyGrant Number
Ministry of Science and Higher Education (Russia)05.619.21.0016
Russian Science Foundation21-12-00343
Heising-Simons FoundationUNSPECIFIED
Ministry of Science and Higher Education (Russia)075-15-2020-778
M.V. Lomonosov Moscow State UniversityUNSPECIFIED
Kazan Federal University0671-2020 0052
Subject Keywords:accretion, accretion discs – black hole physics – quasars: supermassive black holes –X-rays: galaxies – transients: tidal disruption events
Issue or Number:3
Record Number:CaltechAUTHORS:20220107-533928000
Persistent URL:
Official Citation:S Sazonov, M Gilfanov, P Medvedev, Y Yao, G Khorunzhev, A Semena, R Sunyaev, R Burenin, A Lyapin, A Meshcheryakov, G Uskov, I Zaznobin, K A Postnov, A V Dodin, A A Belinski, A M Cherepashchuk, M Eselevich, S N Dodonov, A A Grokhovskaya, S S Kotov, I F Bikmaev, R Ya Zhuchkov, R I Gumerov, S van Velzen, S Kulkarni, First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6, Monthly Notices of the Royal Astronomical Society, Volume 508, Issue 3, December 2021, Pages 3820–3847,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112794
Deposited By: Tony Diaz
Deposited On:09 Jan 2022 00:45
Last Modified:09 Jan 2022 22:13

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