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astro-ph.HE · High Energy Astrophysical Phenomenaastro-ph.GA · Astrophysics of Galaxies

Swift data exclude a third outburst of AT2018fyk with a rise in the predicted 2025 window and more than 0.06 times the 2022 UV excess or 0.42 times the 2022 X-ray rate, if it has the same shape

AT2018fyk is a repeating partial tidal disruption event at z = 0.059. Its X-ray emission decreased suddenly in 2020 and in 2023. Pasham et al. (2024) predicted that a third outburst starts to rise on 2025-07-08 +/- 54 days. We did our own photometry of all public Swift/XRT and Swift/UVOT data from 2022 to 2026 and of two XMM-Newton observations (2023-06-08 and 2024-05-16). We calibrated the XRT count rate with the published 2022 luminosities and reproduced the published 2023 Swift stacks within their 1-sigma errors. No Swift/XRT observation or stack from 2023-12-22 to 2026-09-28 shows a source: 26 observations (34.8 ks) give 47 counts for 44.1 background counts, and L(0.3-10 keV) < 2.1e41 erg/s (3 sigma). We used the 2022-2023 XRT light curve as a template, scaled by an amplitude f, and changed the date T3 of the first detection in 2-day steps. For a rise in the predicted +/-1-sigma window and a delay of 0-52 days to the first detection, f < 0.42 (99.73 % bound). A full repeat (f = 1) is excluded (TS > 25) for T3 from 2023-12-22 to 2025-12-05. The X-ray data alone exclude a repeat that is fainter by the same factor as outburst 2 relative to outburst 1 (f = 0.06-0.18) only for T3 from 2024-02-24 to 2025-06-22. Swift/UVOT shows no UV excess above the 2024 host level in 2025-2026 (largest excess 2.4 sigma in 37 images; trials-corrected p = 0.28). With the 2022-2023 UV excess as a second template, 29 UVOT images give f_UV < 0.06 for T3 from 2025-03-16 to 2025-12-05 (< 0.12 with one filter only). This includes the full predicted window. In the UV, outburst 2 had 0.16-0.23 times the peak excess of outburst 1. Thus a third outburst that decreases by the same factor did not start in this interval, if its UV emission has the 2022 shape. Near day ~2400 after discovery (Wevers et al. 2023), f_UV < 0.03 and the X-ray f < 0.062. XMM-Newton EPIC-pn detected AT2018fyk at 6.6 sigma on 2024-05-16, with L of approximately 9e40 erg/s. This is a faint soft plateau, not a new outburst. Limits: after 2025-12-06, Swift observed for only 78 s, so a faint later outburst is not tested. UV and X-ray emission can change independently, so an outburst with little UV emission is possible. The package contains the code, our measurements, the data URLs and the steps to reproduce all results.

tidal disruption events · repeating partial tidal disruption · AT2018fyk · Swift XRT · Swift UVOT · XMM-Newton · X-ray transients · upper limits · light-curve template · orbital period prediction · supermassive black holes · prediction test · ultraviolet photometry

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References

7
  1. usesdoi:10.3847/2041-8213/ad57b3

    This work tests the orbital ephemeris of this paper (third rise on 2025-07-08 +/- 54 days) and uses its published Swift, XMM-Newton and Chandra luminosities and 2023 Swift stacks for calibration and validation. A full repeat in the predicted window is excluded. A repeat with more than 0.06 times the 2022 UV excess did not start in the predicted window. A UV-faint or later repeat is still possible.

  2. usesdoi:10.5281/zenodo.10913475

    The published X-ray luminosities and UVW1 fluxes of AT2018fyk (CC BY 4.0) are used for the count-rate calibration, the validation, the outburst energies and the UV validation. Copies are included without change.

  3. doi:10.3847/2041-8213/ac9f36

    This paper identified AT2018fyk as a repeating partial tidal disruption event and predicted a return near day ~2400 after discovery. We give an upper bound on the amplitude of a 2022-like outburst near that date.

  4. doi:10.3847/1538-4357/ad4da3

    Alternative model of AT2018fyk: one disruption near a black-hole binary. We discuss it as a possible reason for the missing third outburst.

  5. doi:10.48550/arXiv.2606.06578

    This paper reports that the predicted third flares of two other repeating TDE candidates did not occur. Our result for AT2018fyk is a similar case.

  6. doi:10.48550/arXiv.2609.33809

    Review of observations of repeating tidal disruption events, used for background.

  7. doi:10.48550/arXiv.2602.18698

    Model of accretion-disk state changes in repeating partial TDEs. It explains why a later outburst can be fainter in X-rays.

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