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

ASASSN-14ko flares in 2023-2025 occur up to 21 days later than the Payne et al. 2022 ephemeris predicts, and the period decrease became slower after 2021

ASASSN-14ko is a nuclear transient in ESO 253-G003 with flares that repeat approximately every 115 d. Payne et al. (2022) published a timing model with a period derivative Pdot = -0.0026, fit to flares up to 2021 November. We tested this model with data that it did not use: ASAS-SN Sky Patrol v2 g-band photometry to 2025 February, our own aperture photometry of 382 Swift/UVOT visits (2020-2026), and TESS full-frame-image photometry, which includes sector 98 (2025 October-November). We measured flare times with several markers (UV peak, optical half-rise, template shift, polynomial peak). We calibrated the offset of each marker on 2018-2021 flares. After 2022 the flares occur later than the published prediction: by +3 to +6 d in 2022-2023, by +6 to +17 d in 2023-2024, and by +21 d in 2025 November (TESS). Three instruments agree. From the Swift-UV-peak and optical-rise markers, the local period decreased by 0.41 +/- 0.09 d per cycle in 2018-2021 but by only 0.12 +/- 0.06 d per cycle in 2021-2025 (z = 2.7, approximate). The mean local period in 2023-2025 is 107.45 +/- 0.32 d. The Payne et al. 2022 model predicts 105.3 d. The strength of the evidence for a change of Pdot depends on the data set. A re-fit of the published 2014-2021 peak times with a free jitter (Pdot = -0.00214) still agrees with the 2022-2025 times (p = 0.26), because its forecast spread is +/- 3-8 d. A re-fit with the Payne et al. error treatment (Pdot = -0.00234) is rejected by the optical-rise times (p = 0.003). Joint fits prefer a change of Pdot near 2021 by Delta BIC = 4.8 to 32. Limitations: we had no ground-based optical data after 2025 February; flare shapes changed in 2022-2023, so the flare markers can shift; our UVOT photometry does not use the HEASoft pipeline. We give forecasts for the 2026-2027 flares (for example, a peak near 2026-11-18 if the 2023-2025 period stays constant, against 2026-10-18 from the Payne et al. 2022 model). These forecasts can be tested directly.

ASASSN-14ko · ESO 253-G003 · repeating nuclear transient · partial tidal disruption event · flare timing · period derivative · ephemeris forecast test · Swift UVOT · TESS · ASAS-SN · out-of-sample test

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References

11
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    Source of the tested timing model (P0 = 115.2 d, Pdot = -0.0026) and of the 2020-2021 published peak times. Our data show that the flares after 2022 occur later than this model predicts.

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  10. useshttps://heasarc.gsfc.nasa.gov/FTP/swift/data/obs/

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  11. useshttps://registry.opendata.aws/tess/

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