Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT), an international team of astronomers has observed a tidal disturbance event known as AT 2022cmc. The results of the surveillance campaign, presented in a paper published Jan. 2 on arXiv Prepress server, can shed more light on the nature of this event.
Tidal perturbation events (TDEs) are an astronomical phenomenon that occurs when a star passes close enough to a supermassive black hole and is torn apart by the black hole’s tidal forces, causing the perturbation process. This tidal-disrupted stellar debris begins to fall onto the black hole and ejects radiation from the innermost region of the accretion debris, an indication of the presence of TDE.
Some TDEs show strong and long-lasting X-ray emission with a rapid change accompanied by radio emission, attributed to synchrotron radiation. They are supposed to have relativistic jets, so they are also known as relativistic or “flowing” TDEs.
AT 2022cmc was detected by the Zwicky Transient Facility (ZTF) as a fast, red transient at a redshift of 1.193. Subsequent observations of this source after its discovery found that a relativistic jet directed towards Earth had formed which led to an afterglow powered by synchrotron radiation. Moreover, it turned out that the transient experienced a rapid (and red) initial decay phase at optical/ultraviolet wavelengths, followed by a blue-luminous plateau (−22 mag) with a duration of about 4.5 days after detection in the resting window. Therefore, AT 2022cmc is classified as the optically bright relative TDE.
In order to further investigate the nature of AT 2022cmc, a group of astronomers led by Alexandre Seykota of ESO made linear and polar circular optical observations of this TDE using the Focal Reducer/Low Dispersion Spectrum 2 (FORS2) mounted on the VLT.
“Linear and circular polarimetry of AT 2022cmc was performed using VLT/FORS2 in the R band during its plateau phase, on February 27, 2022, and March 10, 2022 (7.22 and 12.23 days post-discovery resting window), respectively,” the researchers wrote in the paper.
The observations did not reveal any obvious linear or circular polarization for AT 2022cmc. The astronomers explained that the degree of linear polarization was very low, at a level of 0.14 – and therefore lower than what was observed for the other two relativistic TDEs, namely: Swift J164449.3 + 573451 and Swift J2058 + 0516. When it comes to the degree of circular polarization – it was measured to be -0.3 approximately, therefore also very low.
According to the paper’s authors, the lack of polarization detection confirms that AT 2022cmc is a relative TDE. They added that the observed emission during the monitored phases most likely originates from a thermal component of TDE, which is axially symmetric and projected onto the electrode.
The scientists emphasized that their research proves how important spectral observations of the rapidly fading optical components of new streaming TDEs are in real time. Such studies can help us better understand the origin of TDE emissions.
Alexander Seykota et al. Linear and circular polarimetry of an optically bright relative tidal disturbance event at 2022 cm c, arXiv (2023). DOI: 10.48550/arxiv.2301.00499
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