AstroNote 2026-106

We report on the ongoing multi-band photometric monitoring campaign of SN 2026ayt, conducted through the BHTOMnetwork. SN 2026ayt was discovered by ATLAS (with o-band) on January 20, 2026 (Tonry et al. 2026). It was classified as Type II SN with z = 0.0036, based on the presence of broad H-alpha and H-beta features superimposed on a blue continuum (Jacobson-Galan 2026).

Photometric follow-up by the BHTOM.spacenetwork commenced on January 22, 2026, just two days after initial discovery, and is still ongoing. Photometric follow-up has been carried out by the 1-m LCO Network, 50-cm University of Zielona Góra Entre encinas y estrellas (Spain), 51-cm Slooh Australia Telescope (Australia), 41-cm Ritchey-Chretien telescope (CTIO, Chile), 41-cm PROMPT-2 Telescope (CTIO, Chile), 40-cm PROMPT-6 Telescope (CTIO, Chile) and 35-cm Perth Observatory (Australia). Photometric observations were taken in g, r, i, z, B, V, I & R filters and subsequently transformed into Gaia Synthetic Photometry (GaiaSP) for consistency.

Following the peak, the light curve demonstrates a clear and sustained plateau-like phase with the r and i band magnitudes holding at ~ 14.7 - 14.1 mag. The g-band sits systematically fainter than the r and i-bands during the plateau, with the colour difference (g-r) gradually increasing. This progressive reddening supports the cooling of the photosphere. The UV channels (W1, W2 and M2) from Swift UVOT show a rapid post-peak decline, as expected from the cooling of the photosphere. The observed plateau duration of >60 days and amplitude are broadly consistent with canonical Type II-P behaviour driven by hydrogen recombination in the expanding ejecta. Further photometric monitoring will help to better understand its behaviour.

Detailed light curves and associated statistics are presented on the webpage: https://bhtom.space/public/targets/AT2026ayt. Further details and the full photometric dataset are available for download by registered users of the BHTOM.space platform.

Acknowledgements: BHTOM.space is based on the open-source TOM Toolkit by LCO and has been supported by the European Union's research and innovation programmes under grant agreements No 101004719 (OPTICON-RadioNet Pilot, ORP) and 101131928 (ACME).