Unveiling the nature of SN 2022jli: The first double-peaked stripped-envelope supernova showing periodic undulations and dust emission at late times

We present optical and infrared observations from maximum light until around +800 days of supernova (SN) 2022jli, a peculiar stripped-envelope (SE) SN showing two maxima, each one with a peak luminosity of about $3 \times 10^{42}$ erg s$^{-1}$, separated by 50 days. The second maximum is followed by unprecedented periodic undulations with a period of $P \sim 12.5$ days. The spectra and the photometric evolution of the first maximum are consistent with the behaviour of a standard SE SN with an ejecta mass of $\sim 1.5$ $M_{\odot}$ and a radioactive $^{56}$Ni mass of $\sim 0.12$ $M_{\odot}$. The optical spectra after +400 days relative to the first maximum correspond to a standard SN Ic event, and at late times SN 2022jli exhibits a significant drop in the optical luminosity, implying that the physical phenomena that produced the secondary maximum have ceased to power the SN light curve. Among other potential scenarios, we discuss how the second maximum could be powered by a magnetar, while the light curve periodic undulations could be produced by accretion of material from a companion star onto the neutron star in a binary system. The near-infrared spectra shows clear first CO overtone emission from about +190 days after the first maximum, and it becomes undetected at +400 days. A significant near-infrared excess from hot dust emission is detected at +238 days, having been produced by either newly formed dust in the SN ejecta or a strong near-infrared dust echo. Depending on the assumptions of the dust composition, the estimated dust mass is $2-16 \times 10^{-4}$ $M_{\odot}$. The potential magnetar power of the second maximum can fit into a more general picture in which magnetars are the power source of SE super-luminous SNe, and could explain bumps, undulations, and late-time excess emission in SE SNe.

💡 Research Summary

The paper presents an extensive observational campaign of the stripped‑envelope supernova SN 2022jli, covering optical and near‑infrared (NIR) data from shortly before maximum light to roughly +800 days after explosion. The object was discovered in the nearby galaxy NGC 157 and quickly classified as a Type Ic SN. Its light curve is remarkable for displaying two nearly identical peaks (each ≈3 × 10⁴² erg s⁻¹) separated by about 50 days. The first peak behaves like a normal SE‑SN, and modelling of the bolometric light curve yields an ejecta mass of ~1.5 M☉ and a ⁵⁶Ni mass of ~0.12 M☉.

The second peak, however, is followed by a striking series of quasi‑periodic undulations with a period of ~12.5 days that persist for several cycles. This phenomenon has never been seen in SE‑SNe. The authors explore two main physical explanations. A magnetar spin‑down model can reproduce the luminosity of the second peak and the subsequent rapid decline, but it does not naturally generate the observed periodicity. An alternative “super‑Eddington accretion” scenario invokes a binary system where a newly formed neutron star accretes material from a companion at each periastron passage; the resulting variable accretion rate could produce the 12.5‑day oscillations. The paper suggests that both mechanisms may operate simultaneously, with the magnetar providing the bulk energy for the second maximum and the binary accretion imprinting the periodic modulation.

Spectroscopically, the SN shows typical Type Ic features during the first peak. Starting at +190 days, the NIR spectra reveal the first overtone band of carbon monoxide (CO), confirming molecule formation in a stripped‑envelope environment. The CO emission fades by +400 days, likely due to dissociation or obscuration. Around +238 days, the NIR photometry exhibits a clear excess consistent with hot dust (temperature ≈1500 K). By fitting a simple black‑body dust component, the authors estimate a dust mass of 2–16 × 10⁻⁴ M☉, depending on grain composition. This dust could be newly condensed in the ejecta or arise from a light echo off pre‑existing circumstellar dust.

The authors place SN 2022jli in context with other double‑peaked SE‑SNe such as SN 2005bf, PTF 11mnb, and SN 2019cad, noting that none of those events displayed periodic undulations. They also compare it to SN 2022xxf, where a massive hydrogen‑poor circumstellar shell was invoked to explain a second peak; however, the periodicity and CO/dust signatures in SN 2022jli point to a different underlying physics.

In conclusion, the study demonstrates that (i) molecule and dust formation can occur in SE‑SNe, (ii) magnetar energy injection remains a viable explanation for unusually luminous secondary maxima in stripped‑envelope explosions, and (iii) binary interaction—specifically episodic accretion onto a compact object—can imprint regular light‑curve modulations. The authors advocate for follow‑up high‑resolution radio, X‑ray, and polarimetric observations, as well as three‑dimensional hydrodynamic simulations, to disentangle the relative contributions of magnetar spin‑down and binary accretion, and to further probe the chemistry of SE‑SN ejecta.