Optical Polarimetry of the Tidal Disruption Event AT2019DSG

Abstract

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.

A concordance scenario for the observed neutrino from a tidal disruption event

“…Indeed, for a large enough black hole spin, a jet may be expected in a unified picture of TDEs in addition to a mildly relativistic outflow 24 , which has been (indirectly) observed 17 . A preliminary support to the jet hypothesis also comes from optical polarimetry of AT2019dsg 23 .…”

“…The radio emission has been interpreted as an indication for a mildly relativistic outflow present over the timescale of the neutrino event. Furthermore, optical polarimetry observations of this TDE cannot be uniquely interpreted, and may provide some hint for a relativistic jet 23 . A further noteworthy element is that out of the 17 TDEs in the ZTF sample, only 4 were found to have a counterpart in X-rays; of these, AT2019dsg was the one with the highest sustained (over several days) X-ray luminosity.…”

Polarimetry of the superluminous transient ASASSN-15lh

“…Higgins et al (2019) reported a single epoch of V-band polarimetry of OGLE16aaa, measuring 1.81 ± 0.42 per cent, which is of similar magnitude to the polarization measured for ASASSN-15lh by us. Lee et al (2020) observed an evolution in the polarization of AT 2019dsg, with the degree of polarization decreasing from 9.6 ± 2.6percent (at 4 d after light-curve maximum) to 2.0 ± 1.0 per cent (34 d later). Rather than indicating a change in geometry, Lee et al (2020) suggested this was due to non-thermal, relativistic emission from a jet at early times.…”

“…Lee et al (2020) observed an evolution in the polarization of AT 2019dsg, with the degree of polarization decreasing from 9.6 ± 2.6percent (at 4 d after light-curve maximum) to 2.0 ± 1.0 per cent (34 d later). Rather than indicating a change in geometry, Lee et al (2020) suggested this was due to non-thermal, relativistic emission from a jet at early times. The only spectropolarimetric observation of a TDE, reported to date, is of AT 2018dyb at a single epoch (Holoien et al 2020).…”

Theoretical interpretation of the observed neutrino emission from Tidal Disruption Events

“…In addition, we expect efficient particle acceleration in the jet, and our requirements for the acceleration efficiency are moderate. Although a relativistic jet has not been directly observed, there are some indications from optical polarimetry measurements [24], and even the radio signal may be interpreted as due to a relativistic jet in non-vanilla models [11]. In Ref.…”