AstroNote 2024-328

AT 2024zau/ZTF24abmzcpa was first detected as an optical transient in ZTF forced photometry (Masci et al., arXiv:2305.16279) on 2024 Oct. 8.43 UT at g=21.12 +/- 0.28 AB mag and reported to TNS 2024 Oct 24.45 (Sollerman et al., TNS Astronomical Transient Report No. 230230). It has since risen to g=18.95 mag and appears to be nearing maximum light. The source was identified as part of regular ZTF scanning for TDE-like transient light curves due to its consistent blue colors (g-r ~ -0.2 mag) and rise time of one month. This source was flagged by the ML classifier tdescore (Stein et al., 2024, ApJL, 965, L14) due to its blue colors and lack of evidence for AGN activity. We note that this source was also identified by NEEDLE (Aamer et al.; AstroNote 2024-317) as a possible SLSN candidate.

An optical spectrum (range 3500-10500 Angs) was obtained on 2024 Nov 09.45 UT with the Kast spectrograph on the 3 m Shane telescope at Lick Observatory. The spectrum reveals a blue continuum with several broad (FWHM > 10,000 km/s) emission lines consistent with He II 4686 Angs and Balmer lines at a redshift of z~0.085. At this redshift, the faint (r=20.0 AB mag in Legacy Survey imaging) host galaxy has an absolute magnitude of M_r ~ -18.0 mag.

The consistent blue colors and spectral features lead us to classify AT 2024zau/ZTF24abmzcpa as a TDE-H+He, confirming the classification of Charalampopoulos et al. (TNS Classification Report No. 18615). In addition, we note that the He II 4686 line is stronger than H-alpha. Follow up observations with the Neil Gehrels Swift Observatory have been requested.