AstroNote 2025-99

On UT 2025 March 11 (dt=70 d in the rest frame) the Very Large Array (VLA) observed the position of AT2024aehp, a luminous fast blue optical transient candidate at z=0.170 (AstroNote 2024-386), using the X-band (10 GHz) receiver (program ID 24B-338, PI Ho). The X-band image RMS was 5 uJy in 36 minutes of on-source time. A source is detected at the position of AT2024aehp, resulting in a flux density measurement of ~26 uJy (~3 sigma). This source is not present in earlier VLA observations (AstroNote 2025-3). Additional observations were performed by the VLA on 2025 March 15 (dt=73 d in the rest frame) using the C, X, and Ku (6, 10, 15 GHz) receivers. The source is detected in all bands, with a spectral index of β~1.5 where f_v~v^β. The 10 GHz luminosity of the March 11 observation is 2e28 erg/s/Hz, a factor of ~2 lower than the radio luminosity of AT2018cow at a similar observation frequency and epoch (Margutti et al. 2019, ApJ, 872, 18).

We highlight that, although the self-absorbed radio SED and radio luminosity are characteristic of AT2018cow-like transients, the flattening in the optical light curve (AstroNote 2025-3) has not been previously observed in this type of transient. 

Further observations are planned. We thank the observatory staff for rapidly scheduling and executing these observations.