AstroNote 2025-9

AT 2024aepd/ZTF24abyhjvc (RA = 15:25:39.284, Dec = +17:40:50.53) was discovered on 2024-12-05 (MJD = 60649.55), in the nucleus of the galaxy SDSS J152539.29+174050.3 (no spectroscopic redshift, photoZ: 0.099 ± 0.0353). It rose to a peak within ~ 23 days (MJD ~ 60672) and slowly declines since then. Throughout its evolution it shows persistent blue optical colours (ZTF g-r = -0.43 at peak; corrected for MW reddening: E(B-V) = 0.0411, Av = 0.1291). 

We obtained two NOT/ALFOSC optical spectra (MJDs 60678.27 and 60684.23; roughly +6 and +12 days after peak) in order to classify the transient. The spectra are blue and show broad emission lines. At a redshift of z~0.0835, those lines can be identified as Halpha, a blend of Hbeta, HeII 4686 and NIII 4640, and potentially NIII 4100 (see attached screenshot). There are no evident host galaxy lines, potentially Ca H&K however the identification is not robust. At this redshift, the peak absolute magnitude in the g-band is M_g = -20.09 (corrected for MW reddening). Classification tools do not return robust matches, however we get a best match with TDE ASASSN-14li at a redshift of z = 0.0833 using NGSF (Next Generation SuperFit; AstroNote 2022-191, Howell et al. 2005 2005ApJ...634.1190H). Based on the spectra, the location of the transient, the absolute magnitude and its persistent blue optical colours, we tentatively classify AT 2024aepd as a tidal disruption event. Further follow-up is encouraged.