AstroNote 2025-255

The BHTOM.space network coordinated an observing campaign to monitor AT2025ggn, reported on 2025/03/30 by the All Sky Automated Survey for SuperNovae (ASAS-SN) and designated as ASASSN-25ax. The event was spotted in the Dorado constellation within the boundaries of the Large Magellanic Cloud.

Observations commenced on Apr 1st, 2025, approx. 2 days after it was discovered, and continued through July 28th, 2025 and are still ongoing. During this period, approximately 500 measurements were obtained using a 40-cm telescope from the ROAD Observatory (Chile) and the GoChile-T1 telescope of the Nova Gorica University (Chile). Photometric data were taken in various filters and subsequently transformed into Gaia Synthetic Photometry (GaiaSP) for consistency.

AT2025ggn brightening was previously detected by the ATLAS survey (in orange and cyan bands) on March 11, 2025. The object has been fading over the past three months, approximately 13.2 mag in the ATLAS orange band to about 16.6 mag, which is close to the object’s brightness before the brightening (approx. 16.8 mag). Taking into account the duration of the phenomenon and the scale of the brightness change, we hypothesise that it could have been a nova explosion in the LMC, which was also considered by K. Stanek (https://www.wis-tns.org/object/2025ggn/discovery-cert). Although the brightening may be considered too low to confirm a nova explosion, the sheer density of the stellar environment in the LMC region may suggest that the progenitor of the transient was in fact a much dimmer star than the closest visible source, 2MASS J05033739-6924111, a Be star candidate (Sabogal B.E. et al. 2005). The event’s light curve does not show any features of Be-type variability.

Observations of the object will continue until its brightness returns to the baseline level. Spectroscopic observations would have been very useful to determine the true nature of the event.

Detailed light curves and associated statistics are presented on the webpage: https://bhtom.space/public/targets/AT2025ggn. 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).