AstroNote 2025-77

AT2025ccg (ZTF25aafywpr) was identified as a candidate Tidal Disruption Event (TDE) using the Neural Engine for Discovering Luminous Events (NEEDLE) classifier (Sheng et al. 2024), a machine-learning tool for identifying rare astronomical transients (TDEs and Superluminous Supernovae; SLSNe) from real-time alerts from the Zwicky Transient Facility (ZTF; Bellm et al. 2019; Graham et al. 2019) streamed via the Lasair alert broker (Williams et al. 2024), with furture application for Vera C. Rubin Observatory's Legacy Survey of Space and Time Survey. Classification predictions are publicly provided as annotations on Lasair.

2025ccg was initially flagged as a SLSN candidate from NEEDLE given its blue and faint host and apparent r-band magnitude of 19.9+/-0.2 on 2025-02-20. Following closer visual inspection, the apparent nuclear location of the source (offset 0.15" N, 0.17" E from the galaxy centre), made 2025ccg a viable TDE candidate. 

We classify 2025ccg as a TDE based on a spectrum taken by Liverpool Telescope using the SPectrograph for the Rapid Acquisition of Transients (SPRAT; resolution 4.6A/pix) on 28-02-2025. The spectrum shows a blue continuum, and a strong blended N III + He II emission feature at 5600A in the observer frame. Template matching with SNID (Blondin & Tonry 2007 2007ApJ...666.1024B) using the Super-SNID templates (https://github.com/dkjmagill/QUB-SNID-Templates/) provides good matches to TDEs at z=0.20 (plots attached). We confirm this redshift from strong Ca H&K host absorption lines present within the spectrum. Given the lack of balmer features within the spectrum, we classify this event as a TDE-He. 

At a redshift of z=0.20, the current luminosity of TDE2025ccg is M=-21.2+/-0.2. The light curve appears to be still rising in the ZTF photometry (https://lasair-ztf.lsst.ac.uk/objects/ZTF25aafywpr/), making it unusually luminous for a TDE-He, and may also explain the initial NEEDLE classification as a SLSN. We encourage spectroscopic follow-up of this event.

NEEDLE has now successfully identified 7 candidates which have been publicly confirmed as spectroscopic TDEs. All of these events were identified prior to maximum light.