Multi-Messenger Predictions for T Coronae Borealis: Probing Particle Acceleration in Novae

TL;DR

This paper tackles the problem of distinguishing hadronic versus leptonic origins of gamma-rays in novae by focusing on T CrB, a closer recurrent nova expected to erupt soon. Building on RS Oph results, it implements two hadronic acceleration channels—external shocks (ES) in the interaction between nova ejecta and the red-giant wind, and magnetic reconnection (MR) near the white dwarf—to predict secondary gamma-ray and neutrino fluxes, incorporating source absorption, propagation, and flavor oscillations. It finds that ES predicts gamma-rays detectable by current gamma-ray facilities but neutrinos remain challenging to detect, while MR can significantly boost high-energy neutrino fluxes, potentially observable by IceCube and KM3NeT, albeit with gamma-ray absorption close to the source. A key diagnostic is the possible time delay between MR- and ES-origin signals, offering a path to constrain nova particle acceleration; joint gamma-ray–neutrino observations will be essential given the substantial model uncertainties. Overall, the work provides the first model-based multimessenger predictions for T CrB and highlights how detections or non-detections in gamma-rays and neutrinos can reveal the dominant acceleration mechanism in novae.

Abstract

The MAGIC detection of near-TeV gamma-rays from the 2021 outburst of the recurrent nova RS Ophiuchi (RS Oph) has established it as a TeV-scale particle accelerator. However, the underlying production mechanism --\textit{hadronic} versus \textit{leptonic}-- remains uncertain due to the non-detection of coincident neutrinos at IceCube. Indeed, the neutrino flux predicted by the hadronic model for RS Oph was below IceCube sensitivity. T Coronae Borealis (T CrB), a nova similar to RS Oph, is anticipated to undergo an outburst soon. Being closer to Earth (0.8 kpc versus 2.45 kpc for RS Oph), T CrB is expected to yield a higher neutrino flux, making the upcoming outburst a once in a lifetime opportunity to test-and potentially detect-nova neutrinos. In this work, we present the first model-based estimates of the hadronic secondary fluxes from T CrB and assess their detectability with gamma-ray (LHAASO, Fermi-LAT, MAGIC, H.E.S.S., MACE, and HERD) and neutrino (IceCube and KM3NeT) telescopes. We adopt two proton-acceleration mechanisms: (i) an external shock (ES) driven mechanism at the interaction ($10^{13}$ cm) of nova ejecta and the red giant wind, and (ii) magnetic reconnection (MR) near the white dwarf surface ($10^{9}$ cm). The latter, arising deep inside the nova system, will fully absorb gamma-rays while allowing only neutrinos to escape. This could potentially produce neutrino signals hours before the ES origin photons or neutrinos-a unique temporal delay signature. For our benchmark ES model, gamma-rays are detectable across all facilities, while the neutrino detection prospect is poor. Only a tiny upper part of the ES model parameter space is above IceCube/KM3NeT sensitivity. In contrast, both observatories have significantly better prospects for detecting neutrinos in the MR scenario.

Figures (7)

• Figure 1: Schematic of the external shock model. The RG is shown by the red star at the center and the WD is depicted by the bright white star on the right. The yellow arrows around the WD represent the nova shockwave propagating into the RG wind shown by the giant red circle.
• Figure 2: Relevant timescales as a function of proton energy, $E_{\rm p}$ at $r=r_{\rm i}$ for a typical RS Oph (2021) like scenario.
• Figure 3: Left: Gamma-ray flux as a function of time (red) integrated in the energy range $50$ MeV-$500$ GeV for RS Oph using ES model. The black data points show the Fermi-LAT measurements HESS:2022qap in the same energy range. Right: Gamma-ray (red) and muon neutrino (blue) fluxes for RS Oph at distance $2.45$ kpc. The green and purple data points show the MAGIC MAGIC:2022rmr and HESS HESS:2022qap data, respectively. The black contour shows the IceCube sensitivity. The muon neutrino flux (blue curve) being far below the IceCube sensitivity explains the non-detection of neutrinos from RS Oph. For both panel, all the model parameters are given in the benchmark values in Tab. \ref{['tab:params']}, except $\epsilon_p$ which is taken to be $0.05$.
• Figure 4: Left: Luminosity of predicted gamma-rays (red) and all flavour neutrinos (blue) as a function of time from T CrB with ES scenario, above energy $10$ GeV. $t_{0}$ is the onset time of gamma-ray and neutrino production. Right: Luminosity of gamma-rays (red) and all flavour neutrinos (black) as a function of energy, averaged over 14 days after the burst. Both figures show spectra without propagation effects.
• Figure 5: Left: Propagation effect on the gamma-ray spectrum due to pair production losses for two different optical luminosities, $L_{\rm opt} = 10^{38}~\rm erg/s$ (red dashed) and $L_{\rm opt} = 10^{39}~\rm erg/s$ (red dashed). The red solid curve shows the flux without absorption. Right: Effect of oscillation on the muon neutrino flux. The blue solid curve shows the $\nu_{\mu}$ flux without oscillation, whereas the blue dashed curve depicts the $\nu_{\mu}$ flux after oscillation.