Independent Discovery of a Probable Nova in M31, AT 2025ahzx

ATel #17558; K. Hornoch (Ondrejov), H. Kucakova (Charles University), A. W. Shafter (SDSU)
on 23 Dec 2025; 20:33 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)

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We report the independent discovery of a probable nova found during our survey of the central region of M31. The object was discovered on a co-added 360-s R-band CCD frame taken in bad seeing conditions on 2025 Dec. 22.026 UT with the Danish 1.54-m telescope at La Silla Observatory.

We found the object as a rather faintly visible possible nova candidate and held its announcement until we took confirmation images to be sure that the object is real. In the meantime, the object was independently discovered on Dec. 22.874 UT by F. Castellani et al. and designated as AT 2025ahzx = TCP J00422844+4118245.

The object was designated by us as M31N 2025-12e and is located at R.A. = 0h42m28s.43, Decl. = +41o18'24".3 (equinox 2000.0), which is 179.1" west and 135.8" north of the center of M31 (see link to discovery image below).

Castellani et al. mentioned possibility that the current transient could be associated with a red supergiant LGGS J004228.48+411825.6. We carefully aligned our R-band coadded image taken on Dec. 23.027 UT with the original R-band LGGS image taken by Massey et al. (2006, AJ, 131, 2478) and the aligned combined image clearly shows that the two objects are spatially separated by about 1.2", and thus the current transient is likely a nova in M31.

The following R-band magnitudes were obtained using the Danish 1.54-m telescope (DK154):

 
  Date [UT]    |  Mag   | Err  | Filter  | Telescope 
 
2025-12-20.024 | >19.8  |      | R       | DK154 
2025-12-22.026 |  18.4  | 0.2  | R       | DK154 
2025-12-23.027 |  17.52 | 0.05 | R       | DK154 
 

As with all extragalactic novae, follow-up spectroscopic and photometric observations to confirm the nova's nature and determine its spectroscopic class and rate of decline (speed class) are encouraged.

Discovery image