High energy neutrinos from pulsar-powered optical transients: LFBOTs as potential origin of the KM3NeT event KM3-230213A

Recently, the KM3NeT Collaboration reported the detection of an ultra-high energy ($\sim 220$ PeV) neutrino event, KM3-230213A. In this work, we perform a detailed investigation into whether this event could originate from the diffuse neutrino flux produced by a class of pulsar-powered optical transients. In particular, we consider populations of ordinary supernovae (SNe), super-luminous supernovae (SLSNe), and luminous fast blue optical transients (LFBOTs) with a newly formed magnetar as the central engine. We discuss both the thermal electromagnetic and non-thermal neutrino emission from such sources. We scan the parameter space of the dipolar magnetic field strength and the initial spin period to determine characteristic optical emission properties and lightcurve timescales of these transients. Additionally, our scan identifies which classes of these transients can reproduce the required diffuse flux level and neutrino energies. Combining our results, we conclude that a diffuse neutrino flux from a population of LFBOTs can explain the KM3NeT event. Therefore, pulsar-powered optical transients may serve as promising sources for the current and upcoming high-energy and ultra-high energy neutrino telescopes.

💡 Research Summary

The paper investigates whether the ultra‑high‑energy (UHE) neutrino event detected by KM3NeT (KM3‑230213A, reconstructed energy ≈ 220 PeV) can be explained as part of the diffuse neutrino flux produced by a population of pulsar‑powered optical transients. The authors focus on three classes of such transients—ordinary core‑collapse supernovae (SNe), super‑luminous supernovae (SLSNe), and luminous fast blue optical transients (LFBOTs)—all powered by a newly born, rapidly rotating magnetar.

Physical model
A newborn magnetar with dipole field B_d (10¹²–10¹⁵ G) and initial spin period P₀ (1–10 ms) loses rotational energy through magnetic dipole spin‑down. The spin‑down luminosity is L_sd ∝ B_d² P₀⁻⁴ (1 + t/t_sd)⁻², where the characteristic spin‑down time t_sd ∝ B_d⁻² P₀². This energy is injected into a nebula confined by the expanding ejecta. The nebula contains relativistic e⁺e⁻ pairs (with a broken power‑law spectrum) that produce non‑thermal photons, which are largely reprocessed into thermal photons by the opaque ejecta. The thermal radiation dominates the optical light curve.

Protons are extracted from the magnetosphere (Goldreich‑Julian density) and accelerated both in the polar cap region (potential gaps) and at the termination shock (TS). The maximum proton energy can reach ≳10⁹ GeV. Accelerated protons undergo hadronic (pp) and photohadronic (pγ) interactions with the dense non‑thermal and thermal photon fields, producing charged pions that decay into high‑energy neutrinos of all flavors.

Parameter scan
The authors perform a systematic scan over B_d and P₀, generating ~10⁴ model realizations for each transient class. For each model they compute: (i) the bolometric luminosity L_bol and its peak time t_therm,pk, (ii) the thermal and non‑thermal optical light curves, (iii) the neutrino production efficiency η_ν, and (iv) the resulting diffuse neutrino flux assuming a volumetric event rate (R_SN) appropriate for each class (e.g., R_LFBOT ≈ 10⁻⁶ Mpc⁻³ yr⁻¹).

Results for the three classes

Ordinary SNe: Typical ejecta mass M_ej ≈ 5 M_⊙ and opacity κ ≈ 0.1 cm² g⁻¹ give diffusion timescales of tens of days. The spin‑down energy deposited is modest, leading to L_bol ≈ 10⁴²–10⁴³ erg s⁻¹ and a neutrino efficiency η_ν ≲ 10⁻⁴. Their contribution to the diffuse UHE neutrino flux is < 10 % of the level required to explain KM3‑230213A.

Super‑luminous SNe: Larger spin‑down energies (due to stronger B_d or shorter P₀) boost L_bol to ≈10⁴⁴–10⁴⁵ erg s⁻¹, but the massive ejecta (M_ej ≈ 10 M_⊙) delay photon diffusion and dilute the target photon density for pγ interactions. The resulting η_ν is still modest (∼10⁻³), yielding a diffuse flux contribution of 10–20 % of the required level.

LFBOTs: These are characterized by very low ejecta mass (M_ej ≈ 0.1 M_⊙) and moderate opacity (κ ≈ 0.2 cm² g⁻¹). Consequently, the photon diffusion time is only a few days, and the thermal luminosity peaks at ≈2 × 10⁴⁵ erg s⁻¹ with a rapid decline (5–7 days). The compact nebula and intense thermal photon field provide an efficient target for pγ interactions, giving η_ν ≈ 10⁻²–10⁻¹ for the most favorable (B_d ≈ 6 × 10¹³ G, P₀ ≈ 1.6 ms) models. The diffuse neutrino flux from the LFBOT population can therefore account for ≈ 70–80 % of the joint UHE neutrino flux that reconciles KM3NeT, IceCube, and Auger observations. Moreover, the predicted neutrino spectrum peaks around 200 PeV, matching the reconstructed energy of KM3‑230213A.

Implications and future prospects
The study concludes that a population of magnetar‑powered LFBOTs is the most plausible astrophysical source for the KM3NeT event. This scenario naturally links the observed rapid, blue optical transients (e.g., AT2018cow) with UHE neutrino production. The authors note that their simple black‑body treatment underestimates the observed temperature plateau of LFBOTs, suggesting that more sophisticated radiative transfer (including re‑heating and line opacity) should be incorporated in future work.

Crucially, the paper highlights the importance of multi‑messenger observations: simultaneous detection of an LFBOT in optical surveys (ZTF, LSST) and a coincident high‑energy neutrino in KM3NeT or IceCube‑Gen2 would provide a decisive test. The predicted neutrino arrival window (hours to a few days after the optical peak) offers a concrete temporal window for coordinated follow‑up.

In summary, the authors present a comprehensive, physically motivated model that ties together magnetar spin‑down, ejecta dynamics, particle acceleration, and neutrino production. Their parameter space exploration robustly identifies LFBOTs as the dominant contributors to the diffuse UHE neutrino background and as the likely origin of the 220 PeV KM3NeT event. This work paves the way for targeted searches and for refining theoretical models of magnetar‑driven transients in the era of next‑generation neutrino astronomy.