AstroNote 2023-273

We report the classification of the optical transient ZTF23abgcesw/AT2023ugy as a tidal disruption event (TDE). ZTF23abgcesw was first detected by the Zwicky Transient Facility (ZTF) on 2023 September 22 at a magnitude of g = 19.72 +/- 0.20 mag and was identified as a TDE candidate due to its blue color. Forced photometry data from ZTF and ATLAS show that the light curve has been rising for around 35 days. 

We observed ZTF23abgcesw on 2023 October 5 with the Double Spectrograph (DBSP) on the Palomar 5-m telescope. The spectrum shows a blue continuum and a broad emission line that is consistent with Halpha at z=0.106 with a full-width half maximum of 3000 km/s. At the same redshift, the Mg I b lines and Ca II infrared triplet in absorption can also be identified.

We requested and obtained one epoch of Swift observation on 2023 October 18. The host-subtracted UVOT (AB) photometry is uvw2=18.21 +/- 0.06 mag, uvm2=18.30 +/- 0.07 mag, and uvw1=18.15 +/- 0.07 mag, implying a UV-optical color of uvm2 - o ~ -0.6 mag. No significant X-ray emission was detected, with a 3-sigma 0.3-10 keV upper limit at 2.4E-3 count/s. Assuming an absorbed blackbody spectral shape with Nh=6.3E+20 cm^-2 and Tbb=80 eV, this corresponds to a luminosity of < 2.0E+42 erg s^-1. Continued Swift monitoring has been requested.