An asymmetric electron-scattering photosphere around optical tidal disruption events

Leloudas, G.; Bulla, Mattia; Cikota, Aleksandar; Dai, Lixin; Thomsen, Lars L.; Maund, Justyn R.; Charalampopoulos, P.; Roth, Nathaniel; Arcavi, I.; Auchettl, Katie; Malesani, D.; Nicholl, M.; Ramírez-Ruiz, E.

doi:10.1038/s41550-022-01767-z

Cited by 11 publications

(39 citation statements)

References 66 publications

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“…They suggest that the origin of polarization in optical TDEs is electron scattering, similar to SNe and kilonovae, and they exclude synchrotron radiation and dust scattering as significant contributors. The polarization is observed to decrease with time, and Leloudas et al (2022) propose that the data is compatible with the formation and evolution of a super-Eddington accretion disk. They further model the polarization with the super-Eddington accretion model of Dai et al (2018) and the radiative transfer code POSSIS (Bulla 2019), yielding polarization predictions between 0% and 6% for different observing angles, values that are broadly consistent with the observations.…”

Section: Discussionmentioning

confidence: 54%

“…Finally, the study by Liodakis et al (2022a) presented time-varying polarization for AT 2020mot, reaching an extraordinary 25% ± 4% in one epoch. This measurement is very hard to explain by reprocessing models (Charalampopoulos et al 2022;Leloudas et al 2022), and the authors favor shock collisions for this TDE.…”

Section: Discussionmentioning

confidence: 90%

“…Polarimetric observations of "ordinary" optical TDEs (van Velzen et al 2020) were scarce until recently, including few measurements of individual events (Higgins et al 2019;Lee et al 2020;Holoien et al 2020). Leloudas et al (2022) gathered spectral polarimetry for a sample of three optical TDEs and demonstrated that the continuum polarization is wavelength independent, while emission lines depolarize the spectrum. They suggest that the origin of polarization in optical TDEs is electron scattering, similar to SNe and kilonovae, and they exclude synchrotron radiation and dust scattering as significant contributors.…”

Section: Discussionmentioning

confidence: 99%

“…Figure 4 shows a comparison of the linear polarization of AT 2022cmc with other transients, including ordinary optical TDEs (Leloudas et al 2022;Liodakis et al 2022b;Patra et al 2022), relativistic (Wiersema et al 2012(Wiersema et al , 2020 and extreme TDEs (ASASSN-15lh; Maund et al 2020), and a sample of GRBs selected from Covino & Gotz (2016) with N > 4 epochs.…”

Section: Discussionmentioning

confidence: 99%

“…We note that the host galaxy of AT 2022cmc is not detected to very faint limits (>24.5 mag; Andreoni et al 2022a), and it can therefore contribute a maximum 6% of the captured light. For this reason, we have not applied any host galaxy dilution correction for the transient polarization (Leloudas et al 2022;Liodakis et al 2022b).…”

Section: Linear Polarimetrymentioning

confidence: 99%

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Linear and Circular Polarimetry of the Optically Bright Relativistic Tidal Disruption Event AT 2022cmc

Cikota¹,

Leloudas²,

Bulla³

et al. 2023

ApJL

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Tidal disruption events (TDEs) occur when a star orbiting a massive black hole is sufficiently close to being tidally ripped apart by the black hole. AT 2022cmc is the first relativistic TDE that was observed (and discovered) as an optically bright and fast transient, showing signatures of nonthermal radiation induced by a jet that is oriented toward the Earth. In this work, we present optical linear and circular polarization measurements, observed with the Very Large Telescope/FORS2 in the R band (which corresponds to the blue/UV part of the spectrum in the rest frame), ∼7.2 and ∼12.2 rest-frame days after the first detection, respectively, when the light curve of the transient had settled in a bright blue plateau. Both linear and circular polarizations are consistent with zero, p lin = 0.14% ± 0.73%, and p cir = −0.30% ± 0.53%. This is the highest signal-to-noise ratio linear polarization measurement obtained for a relativistic TDE and the first circular polarimetry for such a transient. The nondetection of the linear and circular polarizations is consistent with the scenario of AT 2022cmc being a TDE where the thermal component (disk+outflows) is viewed pole-on, assuming an axially symmetric geometry. The presence and effect of a jet and/or external shocks are, however, difficult to disentangle.

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Section: Discussionmentioning

confidence: 54%

Section: Discussionmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Linear Polarimetrymentioning

confidence: 99%

See 3 more Smart Citations

Linear and Circular Polarimetry of the Optically Bright Relativistic Tidal Disruption Event AT 2022cmc

Cikota¹,

Leloudas²,

Bulla³

et al. 2023

ApJL

Self Cite

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Multimessenger astronomy with black holes

D'Orazio,

Charisi,

Derdzinski

et al. 2024

Black Holes in the Era of Gravitational-Wave Astronomy

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Modeling continuum polarization levels of tidal disruption events based on the collision-induced outflow model

Charalampopoulos

Bulla

Bonnerot

et al. 2023

A&A

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Tidal disruption events (TDEs) have been observed in the optical and ultraviolet (UV) for more than a decade, but the underlying emission mechanism still remains a puzzle. It has been suggested that viewing angle effects could potentially explain their large photometric and spectroscopic diversity. Polarization is indeed sensitive to the viewing angle and the first polarimetry studies of TDEs are now available, calling for a theoretical interpretation. In this study, we model the continuum polarization levels of TDEs using the three-dimensional (3D) Monte Carlo radiative transfer code POSSIS and the collision-induced outflow (CIO) TDE emission scenario, where unbound shocked gas originating from a debris stream intersection point offset from the black hole (BH), reprocesses the hard emission from the accretion flow into UV and optical bands. We explore two different cases of peak mass fallback rates Ṁp (∼ 3 M⊙ yr−1 and ∼ 0.3 M⊙ yr−1) while varying the following geometrical parameters: the distance Rint from the BH to the intersection point where the stellar debris stream self intersects; the radius of the photosphere around the BH Rph, on the surface of which the optical and UV photons are generated; and the opening angle Δθ that defines the fraction of the surface of the photosphere on which the photons are generated (anisotropic emission). For the high mass fallback rate case, we find for every viewing angle polarization levels below one (P < 1%) and P < 0.5% for ten out of 12 simulations. The absolute value of polarization reaches its maximum (Pmax) for equatorial viewing angles. For the low mass fallback rate case, the model can produce a wide range of polarization levels for different viewing angles and configurations. The maximum value predicted is P ≈ 8.8% and Pmax is reached for intermediate viewing angles. We find that the polarization strongly depends on (i) the optical depths at the central regions (between the emitting photosphere and the intersection point) set by the different Ṁp values and (ii) the viewing angle. With time, there is a drop in densities and optical depths leading to a general increase in polarization values and Pmax, although the opposite trend can be observed for specific viewing angles. Increasing the distance Rint between the intersection point and the BH seems to generally favor higher polarization levels. Finally, by comparing our model predictions to polarization observations of a few TDEs, we attempt to constrain their observed viewing angles and we show that multi-epoch polarimetric observations can become a key factor in constraining the viewing angle of TDEs.

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An asymmetric electron-scattering photosphere around optical tidal disruption events

Cited by 11 publications

References 66 publications

Linear and Circular Polarimetry of the Optically Bright Relativistic Tidal Disruption Event AT 2022cmc

Linear and Circular Polarimetry of the Optically Bright Relativistic Tidal Disruption Event AT 2022cmc

Multimessenger astronomy with black holes

Modeling continuum polarization levels of tidal disruption events based on the collision-induced outflow model

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