A 14-yr-old Mystery: The Peculiar Case of the Engine-driven SN 2012ap

Journal article

We present late-time (δt > 3000 days) optical (Keck), X-ray (Chandra and the Nuclear Spectroscopic Telescope Array), and radio (the Very Large Area, the Atacama Large Millimeter/submillimeter Array, and the Upgraded Giant Metrewave Radio Telescope) observations of the Type Ic-BL (SN Ic-BL) SN 2012ap. Previous studies of this supernova (SN) have suggested that it stands out as a key example of a weak engine-driven explosion due to the lack of gamma-ray burst (GRB) detection and mildly relativistic ejecta. Recently, radio sky surveys revealed the rebrightening of the radio emission from this SN, highlighting the possibilities of a density enhancement at large radii or the existence of an off-axis relativistic jet. While the late-time optical spectra do not exhibit the broad emission lines seen in other interacting supernovae (SNe), our analysis of the broadband radio and X-ray emission implies that both scenarios are plausible. If a density enhancement is responsible for the radio rebrightening, it has to result from a change in the mass-loss rate and/or wind velocity, possibly due to the transition of the progenitor from a red supergiant to a Wolf–Rayet star. If the late-time radio component is a result of an off-axis relativistic jet, we find that an energetic narrow jet viewed at θobs ≥ 80° is needed. In this scenario, SN 2012ap is not a result of a weak engine-driven explosion, and instead, it is similar to other GRBs. However, radio rebrightenings of SN Ic-BL are not enough on their own to determine the existence of off-axis jets, and our planned Very Long Baseline Array observation will help reveal the true nature of this SN.

Authors: Sfaradi, I; Margutti, R; Chornock, R; A. J., N; Wiston, E

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal Letters
• Volume: 1005
• Issue: 1
• Pages: L19
• Article number: L19
• Publication date: 2026-06-24
• Acceptance date: 2026-06-03
• DOI: 10.3847/2041-8213/ae796d
• EISSN: 2041-8213
• ISSN: 2041-8205
• Language: English
• Keywords: Core-collapse supernovae; Radio astronomy; Circumstellar matter; Relativistic jets; Time domain astronomy