A1 Refereed original research article in a scientific journal
Polarimetric diversity in tidal disruption events: Comparative study of low-polarised sources with AT2020mot
Authors: Floris, Alberto; Liodakis, Ioannis; Koljonen, Karri I. I.; Lindfors, Elina; Agis-Gonzalez, Beatriz; Paggi, Alessandro; Blinov, Dmitry; Nilsson, Kari; Agudo, Iván; Charalampopoulos, Panagiotis; Diaz Teodori, María Alejandra; Escudero Pedrosa, Juan; Otero-Santos, Jorge; Piirola, Vilppu; Newsome, Megan; Van Velzen, Sjoert
Publisher: EDP Sciences
Publication year: 2025
Journal: Astronomy and Astrophysics
Article number: A81
Volume: 703
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202555626
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/10.1051/0004-6361/202555626
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/505551146
Context
Tidal disruption events (TDEs) occur when a star is disrupted by the tidal forces of a supermassive black hole (SMBH), which produces bright multi-wavelength flares. Among these events, AT2020mot has so far exhibited the highest recorded optical polarisation, with tidal shocks proposed as the primary source of its polarised emission.
Aims
We present a comprehensive analysis of 13 TDEs with available polarimetric observations, aiming to determine whether the unusually high polarisation of AT2020mot stems from unique physical processes or arises from mechanisms shared by other TDEs.
Methods
We present new optical polarisation measurements of TDEs obtained from multiple ground-based telescopes, combining them with optical, UV, and X-ray light curves from the Zwicky Transient Facility and the Swift observatory. We derived intrinsic TDE properties – such as SMBH and stellar masses – using MOSFiT and TDEMass, and compared them with those of the sample population.
Results
Our population study reveals that AT2020mot aligns with the broader TDE sample in terms of most physical properties, including blackbody temperature, luminosity, and rise timescales. However, its optical polarisation degree is exceptionally high compared to the low or undetected polarisation observed in other events. Additionally, according to our MOSFiT fit, AT2020mot has an elevated column density, which suggests a more complex environment than is typically assumed.
Conclusions
We conclude that although AT2020mot fits well within the general TDE population in terms of global characteristics, its extraordinarily high polarisation and higher column density challenge current models based purely on shock or reprocessing mechanisms. More extensive, time-resolved polarimetric monitoring of newly discovered TDEs will be critical to determine whether AT2020mot represents an outlier or the extreme end of a continuum of TDE properties.
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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. Neither the European Union nor the granting authority can be held responsible for them. 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). 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. PC acknowledges support via Research Council of Finland (grant 340613). MADT acknowledges support from the EDUFI Fellowship and the Johannes Andersen Student Programme at the Nordic Optical Telescope.
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.
