AstroNote 2024-37

We report the classification of the optical transient ZTF20abwtifz/AT2020afhd (RA = 03:13:35.67, Dec = -02:09:06.21, z = 0.024) as a tidal disruption event (TDE) due to its persistent blue optical colors, bright UV flux measured by the Neil Gehrels Swift telescope, and follow-up optical spectroscopy. We also report the detection of soft X-ray emission with Swift XRT.

ZTF20abwtifz/AT2020afhd was first reported to TNS by the Zwicky Transient Facility (ZTF) on 2020 Oct 20. A single g-band detection was made by ZTF on 2020 Oct 20, however the source was not further detected until 2023 Sep 27 with a single r-band detection of r = 20.16 +/- 0.29 mag. On 24 Jan 05, the source began to brighten over the next ~30 days and is currently near its peak with g = 16.92 +/- 0.05 mag and g-r = -0.02. 

A low-resolution optical spectrum was taken on 24 Jan 05 with the SED Machine (SEDm) on the P60 Telescope at Palomar Observatory. This follow-up spectrum displayed broad Balmer emission and broad He II emission characteristic of the TDE-H+He class (van Velzen et al. 2021), and represents a significant change from the archival host galaxy spectrum obtained with the 6dF galaxy survey (Jones et al. 2004). The redshift is confirmed at z = 0.024.

Our Swift follow-up observations on 2024 Jan 30 measure a bright UV flux (host-subtracted) of uvw2 = 16.73 +/- 0.04 mag, uvm2 = 16.91 +/- 0.05 mag, uvw1 = 16.77 +/- 0.05 mag. A 1.5ks Swift XRT observation shows the detection of soft X-ray emission at ~0.18 counts/s corresponding to a flux of 4.5e-12 ergs/s/cm^2 and luminosity of 4.8e41 ergs/s for a luminosity distance of 105 Mpc.

Based on the blue optical colors, follow-up optical spectroscopy, and UV/X-ray detections, we classify ZTF20abwtifz as a TDE. We have requested further X-ray follow-up observations with NICER and XMM-Newton. We will continue Swift monitoring and optical spectroscopic follow-up observations. Further follow-up observations, especially at other wavelengths, are strongly encouraged.