In the early hours of the 14th of July 2025, GOTO-N observed the spiral galaxy NGC 7331 and detected a faint new transient source located close to its centre. This source was assigned the name GOTO25evh, and quickly recognised as a potential young supernova. As with all extragalactic transients discovered by GOTO, it was reported to the Transient Name Server and received its official name of 2025rbs. An AstroNote was also published, highlighting the close distance and young age of 2025rbs and strongly encouraged further follow-up by the wider transient community.
A discovery magnitude of 17 in the GOTO L-band meant that 2025rbs was easily observable for spectroscopic follow-up and it was quickly classified as a type Ia supernova, making it the fourth confirmed, and the first thermonuclear, supernova discovered in NGC 7331.Type Ia supernovae like 2025rbs typically reach a peak brightness around magnitude -19.3, which at the distance of NGC 7331 would result in an apparent magnitude of ~11. This is bright enough to be seen visually through telescopes with apertures >70 mm, however the proximity of the supernova to the core of NGC 7331 makes it more of a challenge.
Since discovery it has quickly become the brightest supernova in the sky as of the 25th of July, with the latest measurements placing it around magnitude 12. A large amount of spectroscopic and photometric data is also being collected by both professional and amateur astronomers and we are excited to continue to observe 2025rbs as it evolves.
