AstroNote 2023-102

AT2023cvb is a nuclear transient first reported to TNS by the ATLAS survey on 2023 March 6. It was first detected by the Zwicky Transient Facility (ZTF) as ZTF23aadcbay on 2023 March 13 at a g-band AB magnitude of 17.18 +/- 0.05 mag. Subsequent ZTF photometry shows a gradual light curve decay. 

AT2023cvb was selected by the ZTF Bright Transient Survey (BTS; Fremling et al. 2020 ApJ 895 32, Perley et al. 2020 ApJ 904 35) for spectroscopic classification. On 2023 April 20, we obtained an optical spectrum with the Double Spectrograph (DSBP) on the Palomar 5-meter telescope. The spectrum shows a blue continuum, host galaxy lines at z=0.071, and a broad emission line around Halpha with a line width of approximately 20,000 km/s, akin to the TDE-H spectral class (van Velzen et al. 2021 ApJ 908 4). A Swift observation obtained on 2023 April 28 yields bright UV detections, with a (host-subtracted) uvm2-r color of -0.8 mag, indicating a high temperature of the post-peak UV/optical emitting component, reminiscent of other known TDEs. No significant X-ray emission was detected in Swift/XRT. 

We classify AT2023cvb as a TDE based on its photometric and spectral properties. Since the optical rise and peak of the transient were missed by optical sky surveys due to Sun constraint, the actual peak of the transient is brighter than the first ZTF g-band detection (absolute magnitude = -20.7). The volumetric rate of such optically over-luminous TDEs is very small, less than 1.8/Gpc^3/yr (Yao et al. 2023 arxiv: 2303.06523). Follow-up observations are strongly encouraged.