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Swift and XMM-Newton data from 2023-2024 show two more X-ray flare cycles of eRASSt J0456-20: the recurrence time stays at 193 days and the flares fade by a factor of two per cycle

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Question: the second main example of fast orbital evolution in a repeating partial tidal disruption event (rpTDE) is eRASSt J0456-20. Liu et al. (2024) used Swift data up to 2023 May. They found that the recurrence time fell from about 300 d to about 190 d in five X-ray cycles, with an indication of a constant value at the end. Did the flares continue, and did the period stay constant? Approach: we reduced all 132 public Swift XRT observations (2021-2026) and 18 public XMM-Newton observations (2021-2024) without HEASoft or SAS. 61 Swift and 11 XMM observations are later than the published data. We fit each cycle with one rise-plateau-drop model and a faint-state floor, and we test forecasts made only from cycles 2-5. Results: cycle 6 (2023 Aug-Oct; up to 37 sigma above the floor in XMM) and cycle 7 (2024 Mar; about 10 sigma in XMM, new) occurred. With the best-measured timing marker, a constant period of 193.4 +/- 3.2 d fits cycles 3-7 (chi2 = 0.7 for 3 dof). The period change is +3 +/- 6 d per cycle, and a decrease faster than 6.8 d per cycle is excluded at 95 percent (the early decrease was 39-72 d per cycle). Constant-period forecasts hit cycles 6 and 7 within 6 d. A constant period-derivative fit to the published onsets misses cycle 7 by about 150 d (z = 2.1). The peak rate and the fluence fall by a factor of 0.50 and 0.49 per cycle; this law, fitted to cycles 2-5, predicts the cycle-6 fluence. A constant floor of about 1e41 erg/s is present between flares. Thus the period stopped changing while the flare output continued to fall. Limitations: pipeline-product photometry with one cross-calibration factor; a simple flare shape (the onset marker moves by up to 30 d); cycle 7 has no observed plateau; cycles 8-12 are not tested because the 2024-2026 data miss or are too shallow for the forecast active phases. We also report that no public data can test the November 2026 ASASSN-14ko forecasts yet.

eRASSt J045650.3-203750 · repeating partial tidal disruption · tidal disruption event · X-ray flares · recurrence time · period derivative · orbital decay · out-of-sample forecast · Swift XRT · XMM-Newton · ASASSN-14ko · flare fading
High Energy Astrophysical PhenomenaAstrophysics of Galaxies

References

10
  1. usesASAS-SN and TESS peak times of ASASSN-14ko flares in 2022-2026 drift 2.2 days per cycle later than the published decaying-period ephemeris; the period stays near 108 days
  2. usesASASSN-14ko flares from 2022 to 2026 peak up to 21 days later than the published constant period-derivative ephemeris; random period changes of about 0.6 days per orbit fit the peak times better
  3. usesASASSN-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
  4. usesSwift data show no third flare of AT2018fyk in the 2025 windows that the repeating partial disruption model predicted; a copy of the 2022 flare that starts before December 2025 is below 5% in UV
  5. uses, supportsdoi:10.1051/0004-6361/202348682
  6. https://arxiv.org/abs/2208.12452
  7. useshttps://heasarc.gsfc.nasa.gov/FTP/swift/data/obs/
  8. useshttps://nxsa.esac.esa.int/
  9. usesdoi:10.1086/170124
  10. usesdoi:10.1086/670067

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  1. A finite flare creates an early allowed branch in the 2024 eRASSt J0456-20 clock test uses
  2. Public ZTF data show a constant AT2023uqm period while its flare fluence grew 1.6-fold per flare; one energy-proportional clock for three periodic nuclear transients fails only for some markers uses, challenges
  3. Period change per unit flare fluence fell at least fourfold after the third passage of eRASSt J0456-20 if cycle 8 had the forecast amplitude; in ASASSN-14ko the result depends on timing noise uses, challenges