AstroNote 2025-224

SN 2024pba was discovered by ATLAS on July 6 2024 14:21:28 UT, it was classified as a type II SN approximately 1 week pre-peak with the spectrum showing a broad ~20,000 km/s H-alpha peak. It reached a peak magnitude in averaged ATLAS data retrieved via the ATLAS forced photometry server (Shingles et al., 2021) of o=17.57±0.03 mag before fading gradually over the course of 7 months with a final detection of o=19.85±0.19 mag on 2025-02-25 05:51:25 UT before becoming Sun-constrained.

On 2025-06-17 04:23:30 UT a bright source was detected by GOTO at a magnitude of 16.54±0.04 in the L band (g+r); it is spatially coincident with the position of 2024pba, with an offset between the mean positions of the two events in GOTO of 0.4±0.2" (~1/3 of a pixel). This was the first observation made by GOTO of this location since February 2025. A source is present in earlier ZTF data (via the Lasair broker, Smith, Williams, Young et al. 2019) and detected several times between 2025-05-20 and 2025-05-30 at r~19.2 mag. These detections hint the rebrightening was already taking place in May 2025, as SN2024pba was observed to be r=20 mag and declining by ZTF in Dec 2024. A subsequent much brighter detection was also seen in ATLAS data, with an initial detection 4 days prior to the GOTO detection, at o=16.71±0.03 mag on 2025-06-13 14:31:57 UT. The source then rose to a peak brightness of o=16.35±0.01 mag on 2025-06-24 13:17:08 UT before beginning a steady decline, with its most recent detections being at L=17.00±0.05 mag on 2025-07-18 03:03:02 by GOTO and o=16.93±0.01 mag on 2025-07-21 13:20:12 UT by ATLAS. Taking the redshift as z=0.01, based on the TNS classification report of SN2024pba (2024TNSCR2389....1S), the two peaks have absolute magnitudes of o=-15.6 and -16.8 mag respectively.

At this time, it is unclear whether this is a rebrightening of SN 2024pba or a new transient that exploded in its near vicinity. Further follow-up observations are strongly encouraged to determine the exact nature of this transient.

GOTO magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).