Optical polarisation of stellar-fed active and quiescent supermassive black holes
Bibliographic record
Abstract
Context. The advent of wide-field optical surveys with multi-wavelength capabilities has been a breakthrough in the detection and characterisation of bright, long-lasting optical flares from supermassive black holes, such as tidal disruption events (TDEs), Bowen flares in active galactic nuclei (AGNs), and changing-look AGNs. Yet, the physical mechanisms powering these diverse transient events remain highly debated. Aims. We aim to provide novel model constraints by utilising broadband optical polarimetry to study five TDEs. Our goal is to enhance the understanding of the reprocessing material involved in TDEs and to compare our findings with similar flaring activity observed in AGNs. Methods. Using the MOPTOP polarimeter on the 2 metre Liverpool Telescope, we conducted a monitoring campaign targeting three optically discovered TDEs (AT2024bgz, AT2024pvu, and AT2024wsd) and two Bowen flares in AGNs (AT2020afhd and AT2019aalc). Results. The three thermal TDEs show low intrinsic polarisation levels (ΔP ≈ 0 − 6%) with stable polarisation angles. The Bowen flares also show variable polarisation degrees (ΔP ≈ 0 − 8%) but significant polarisation angle variability: AT2020afhd exhibited a Δθ = 83 ± 8° shift at 150 days post-optical peak, while the AT2019aalc displayed quasi-periodic swings of Δθ ≈ 40° amplitude starting 190 days after peak brightness. Conclusions. The TDEs of this study are well described by models invoking rapid disk formation and reprocessed emission from optically thick outflows, whereas the Bowen flares reveal more complex reprocessing geometries, potentially consistent with TDEs occurring in AGN gas-rich environments. We find that moderate polarisation is observed at later times for TDEs with low-Eddington ratios and highly extended photospheres. This implies that, as the accretion level declines, we expect more asymmetric reprocessing layers along a given viewing angle. Since the outflow density and velocity depend sensitively on the inclination angle, we expect TDEs with low-Eddington ratios and highly extended photospheres to exhibit varying levels of polarisation. The polarisation of AT2019aalc (Seyfert 1) hints at a clumpy, asymmetric outflow and the presence of a tilted, precessing accretion disk, while the polarisation of AT2020afhd (AGN type 2) is consistent with the detection of a scattered light echo.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".