Optical Polarimetry of the Tidal Disruption Event AT2019DSG

We present time-series imaging polarimetry observations of a nearby tidal disruption event (TDE) AT2019DSG at z = 0.0512 to probe the disruption mechanism and shed light on the accretion process. We obtain linear polarimetry using the Alhambra Faint Object Spectrograph and Camera on board the 2.5 m Nordic Optical Telescope. Our observations showed a polarization at the 9.2% ± 2.7% level early on, decreasing to less than 2.7% (at the 68% confidence level) one month later. While the high level of polarization in the early epoch is similar to that of Swift J164449.3+573451 and Swift J2058+0516, the low level of polarization in the later epoch is in agreement with that of OGLE16aaa. Our results thus show the temporal evolution of optical polarization from a TDE. As the degree of polarization changes over time, it is unlikely to be attributed to host galaxy dust, but may originate from a non-isotropic accreting disk, or associated with the relativistic jet emission.