AstroNote 2024-302

We report the classification of optical transients ZTF24abfuwbm/AT 2024vip and ZTF24abjfuew/AT 2024wsd as tidal disruption events (TDEs). Both sources were selected by the tdescore ML classifier (Stein+2024) as candidate TDEs, primarily due to their persistent blue colour and the lack of AGN-like host signatures, and assigned for spectroscopic follow-up.

ZTF24abfuwbm/AT 2024vip was first detected by ZTF on 2024-09-03, and reported as a transient to TNS on 2024-09-13. The transient was fading at the time of discovery, having only recently emerged from behind the sun, suggesting the peak of this transient was missed. It has remained persistently blue (g-r=-0.3) since discovery with no clear colour evolution.

A first spectrum of ZTF24abfuwbm was taken with the Goodman High Throughput Spectrograph on the 4m SOAR telescope on 2024-09-22 (PI: Andreoni). The classification was inconclusive. A second spectrum was taken with the Low Resolution Imaging Spectrometer (LRIS) at Keck-I on 2024-10-01 (PI: Graham). The spectrum shows several narrow galaxy absorption features (Na I, Ca II, Mg I) at a consistent redshift of z=0.089. The spectrum otherwise shows a blue continuum, with a broad feature which we tentatively identify as He II at 4686 A. This spectrum is similar to other TDEs classified as TDE-He, for example AT 2018iih (van Velzen et al 2021).

Based on the spectrum and lightcurve evolution, we classify ZTF24abfuwbm/AT 2024vip as a probable TDE. At this redshift, the transient had an absolute magnitude of at least M=-19.0 in our g-band observations, but the true peak is likely to have been higher. It is currently at an apparent magnitude of m=19.4 and fading slowly.

ZTF24abjfuew/AT 2024wsd was first detected by ZTF on 2024-09-25, and reported as a transient to TNS on 2024-09-27. The transient was rising at the time of discovery. It has remained persistently blue (g-r=-0.3 mag) with no clear colour evolution during this period.

A classification spectrum was taken with the Double Spectrograph at the Palomar 200-in Hale Telescope on 2024-10-13 (PI: Kasliwal). The spectrum shows a blue continuum, with several broad features. Fitting the spectrum with Next Generation Super Fit (Howell et al. 2005, Goldwasser et al. 2022) yields a good match to TDE AT 2018dyb (TDE H+He) at phase 7 days before peak. The NGSF redshift fit is z=0.06. At this redshift, the broad features would be consistent with He II at a rest-frame wavelength of 4686 A, as well as H-alpha and H-beta.  However, given the width of the broad features, a slightly higher redshift of e.g z=0.08 would also be compatible with this interpretation.

In any case, based on the spectrum and lightcurve evolution, we classify ZTF24abjfuew/AT 2024wsd as a probable TDE. The transient currently has a g-band magnitude of 18.3, corresponding to an absolute magnitude of approximately M=-19, but is still rising.

Swift follow-up has been requested for both transients.