Optical polarization from colliding stellar stream shocks in a tidal disruption event
Ioannis Liodakis, K. I. I. Koljonen, D. Blinov, E. Lindfors, K. D. Alexander, T. Hovatta, M. Berton, A. Hajela, Jenni Jormanainen, K. Kouroumpatzakis, N. Mandarakas, K. Nilsson
Abstract
A tidal disruption event (TDE) occurs when a supermassive black hole rips apart a passing star. Part of the stellar material falls toward the black hole, forming an accretion disk that in some cases launches a relativistic jet. We performed optical polarimetry observations of a TDE, AT 2020mot. We find a peak linear polarization degree of 25 ± 4%, consistent with highly polarized synchrotron radiation, as is typically observed from relativistic jets. However, our radio observations, taken up to 8 months after the optical peak, do not detect the corresponding radio emission expected from a relativistic jet. We suggest that the linearly polarized optical emission instead arises from shocks that occur during accretion disk formation, as the stream of stellar material collides with itself.