A1 Refereed original research article in a scientific journal
Polarisation angle variability in tidal disruption events
Authors: Floris, A.; Liodakis, I.; Koljonen, K. I. I.; Lindfors, E.; Agís-González, B.; Paggi, A.; Blinov, D.; Nilsson, K.; Agudo, I.; Charalampopoulos, P.; Escudero Pedrosa, J.; Piirola, V.
Publisher: EDP Sciences
Publication year: 2026
Journal: Astronomy and Astrophysics
Article number: A378
Volume: 707
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202557658
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202557658
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/523443875
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Context. Tidal disruption events (TDEs) occur when a star is disrupted by the tidal forces of a supermassive black hole, and these events produce bright multi-wavelength flares. Polarimetric measurements of TDEs allow us to disentangle the geometry and the mechanisms characterising the accretion process.
Aims. We carried out the first systematic study of the time evolution of the optical polarisation angle (Θ) in a sample of classified TDEs, combining our own data with all available measurements from the literature, with the goal of testing the currently available models that describe TDE emission.
Methods. We assembled data from all available observing epochs with significant linear polarisation detections (Π − 3σΠ > 0%) for sources with at least two such epochs, and we determined the overall variability trends across the sample in various time frames, such as days from peak time and the fallback time (t0) derived from the different models.
Results. Our final sample comprises 12 transients, including three Bowen fluorescence flares (BFFs). The majority of the sources show significant Θ variability. The distribution of |dΘ/dt| peaks near ∼2° d−1. BFFs tend to display sustained late-time Θ evolution, likely due in part to their slower fading. No universal trend emerges when time is normalised by t0.
Conclusions. Short-timescale Θ variability is common in TDEs and is difficult to reconcile with simple axisymmetric reprocessing models that predict a constant polarisation angle. The observed phenomenology favours scenarios with evolving, non-axisymmetric geometries and/or shocks, possibly coupled with changes in optical depth. Denser polarimetric monitoring, contemporaneous spectroscopy, and X-ray/UV coverage are required to break the remaining degeneracies.
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Funding information in the publication:
AF, IL, AP and BAG were funded by the European Union ERC-2022-STG – BOOTES – 101076343. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. DB acknowledges support from the European Research Council (ERC) under the Horizon ERC Grants 2021 programme under grant agreement No. 101040021. KIIK has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 101002352, PI: M. Linares). Neither the European Union nor the granting authority can be held responsible for them. The IAA-CSIC co-authors acknowledge financial support from the Spanish “Ministerio de Ciencia e Innovación” (MCIN/AEI/ 10.13039/501100011033) through the Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía-CSIC (CEX2021-001131-S), and through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. We acknowledge funding to support our NOT observations from the Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland (Academy of Finland grant nr 306531). E.L. was supported by Academy of Finland projects 317636 and 320045.
