Signatures of secondary acceleration in neutrino flares

High-energy neutrino flares are interesting prospective counterparts to photon flares, as their detection would guarantee the presence of accelerated hadrons within a source, provide precious information about cosmic-ray acceleration and interactions, and thus impact the subsequent modeling of non-thermal emissions in explosive transients. In these sources, photomeson production can be efficient, producing a large amount of secondary particles, such as charged pions and muons, that decay and produce high-energy neutrinos. Before their decay, secondary particles can experience energy losses and acceleration, which can impact high-energy neutrino spectra and thus affect their detectability. In this work, we focus on the impact of secondary acceleration. We consider a one zone model, characterized mainly by a variability timescale $t_{\rm var}$, a luminosity $L_{\rm bol}$, a bulk Lorentz factor $\Gamma$. The mean magnetic field $B$ is deduced from these parameters. The photon field is modeled by a broken power-law. This generic model allows to evaluate systematically the maximum energy of high-energy neutrinos in the parameter space of explosive transients, and shows that it could be strongly affected by secondary acceleration for a large number of source categories. In order to determine the impact of secondary acceleration on the high-energy neutrino spectrum and in particular on its peak energy and flux, we complement these estimates by several case studies. We show that secondary acceleration can increase the maximum neutrino flux, and produce a secondary peak at the maximum energy in the case of efficient acceleration. Secondary acceleration could therefore enhance the detectability of very-high-energy neutrinos, that will be the target of next generation neutrino detectors such as KM3NeT, IceCube-Gen2, POEMMA or GRAND.Comment: 12 pages, 4 figues, submitted to A&

Overview of the EUSO-SPB2 Target of Opportunity program using the Cherenkov Telescope

During the Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) mission, we planned Target of Opportunity (ToO) operations to follow up on possible sources of $\gtrsim 10 \, {\rm PeV}$ neutrinos. The original plan before flight was to point the onboard Cherenkov Telescope (CT) to catch the source's path on the sky just below Earth's horizon. By using the Earth as a tau-neutrino to tau-lepton converter, the CT would then be able to look for optical extensive air shower signals induced by tau-lepton decays in the atmosphere. The CT had a field of view of $6.4^\circ$ vertical $\times$ $12.8^\circ$ horizontal. Possible neutrino source candidates include gamma ray bursts, tidal disruption events and other bursting or flaring sources. In addition, follow-ups of binary neutron star mergers would have been possible after the start of the O4 observation run from LIGO-Virgo-KAGRA. The resulting exposure is modeled using the NuSpaceSim framework in ToO mode. With the launch of the EUSO-SPB2 payload on the 13th May 2023, this summarizes the ToO program status and preliminary data, as available

Neutrino constraints on long-lived heavy dark sector particle decays in the Earth

Recent theoretical work has explored dark matter accumulation in the Earth and its drift towards the center of the Earth that, for the current age of the Earth, does not necessarily result in a concentration of dark matter ($\chi$) in the Earth's core. We consider a scenario of long-lived ($\tau_\chi\sim 10^{28}$ s), super heavy ($m_\chi=10^7-10^{10}$ GeV) dark matter that decays via $\chi\to \nu_\tau H$ or $\chi\to \nu_\mu H$. We show that an IceCube-like detector over 10 years can constrain a dark matter density that mirrors the Earth's density or has a uniform density with density fraction $\epsilon_\rho$ combined with the partial decay width $B_{\chi\to \nu_\tau H}\Gamma_\chi$ in the range of $(\epsilon_\rho/10^{-10}) B_{\chi\to \nu_\tau}\Gamma_\chi \lesssim 3\times 10^{-29}-3\times 10^{-28}$ s$^{-1}$. For $\chi\to \nu_\mu H$, $m_\chi = 10^8-10^{10}$ GeV and $E_\mu>10^7$ GeV, the range of constraints is $(\epsilon_\rho/10^{-10}) B_{\chi\to \nu_\mu}\Gamma_\chi \lesssim 6\times 10^{-29}-1.4\times 10^{-27}$ s$^{-1}$.Comment: 9 pages, 9 figure

Neutrino constraints on long-lived heavy dark sector particle decays in the Earth

Recent theoretical work has explored dark matter accumulation in the Earth and its drift toward the center of the Earth that, for the current age of the Earth, does not necessarily result in a concentration of dark matter (χ) in the Earth's core. We consider a scenario of long-lived $(τ_χ∼10^{28}s)$, superheavy $(m_χ=10^7-10^{10} GeV)$ dark matter that decays via $χ→ν_τ\overline{ν}_τ$ or $χ→ν_μ\overline{ν}_μ$. We show that an IceCube-like detector over 10 years can constrain a dark matter density that mirrors the Earth's density or has a uniform density with density fraction ϵρ combined with the partial decay width $B_{χ→ντ\overline{ν}_τΓ_χ}$ in the range of $(ϵρ/10^{-10})B_{χ→ν_τ}Γ_χ≲1.5×10^{-29}-1.5×10^{-28} s^{-1}$. For $χ→ν_μ\overline{ν}_μ, m_χ=10^8-10^{10} GeV$, and $E_μ>10^7 GeV$, the range of constraints is $(ϵρ/10_{-10})B_{χ→ν_μ}Γ_χ≲3×10^{-29}-7×10^{-28} s^{-1}$

Neutrino propagation in the Earth and emerging charged leptons with nuPyProp\texttt{nuPyProp}

Ultra-high-energy neutrinos serve as messengers of some of the highest energy astrophysical environments. Given that neutrinos are neutral and only interact via weak interactions, neutrinos can emerge from sources, traverse astronomical distances, and point back to their origins. Their weak interactions require large target volumes for neutrino detection. Using the Earth as a neutrino converter, terrestrial, sub-orbital, and satellite-based instruments are able to detect signals of neutrino-induced extensive air showers. In this paper, we describe the software code $\texttt{nuPyProp}$ that simulates tau neutrino and muon neutrino interactions in the Earth and predicts the spectrum of the $\tau$-lepton and muons that emerge. The $\texttt{nuPyProp}$ outputs are lookup tables of charged lepton exit probabilities and energies that can be used directly or as inputs to the $\texttt{nuSpaceSim}$ code designed to simulate optical and radio signals from extensive air showers induced by the emerging charged leptons. We describe the inputs to the code, demonstrate its flexibility and show selected results for $\tau$-lepton and muon exit probabilities and energy distributions. The $\texttt{nuPyProp}$ code is open source, available on github.Comment: 42 pages, 21 figures, code available at https://github.com/NuSpaceSim/nupypro

A la poursuite des accélérateurs cosmiques, à l’aide des particules de haute énergie

The advent of time-domain and multimessenger astronomy opens new perspectives to study the most energetic phenomena of our universe, and understand the mysterious origins of ultra-high-energy cosmic rays (UHECR) and high-energy (HE) neutrinos. Cosmic rays appear as key players in the production of non-thermal and, more generally, multimessenger emissions. In this thesis, we develop several analytical and numerical tools to study the acceleration and interactions of cosmic rays in the vicinity of energetic sources. As HE neutrinos are clear signatures of these processes, we study the detectability of HE neutrino flares from transient sources. We identify two interesting categories of sources, namely pulsars and tidal disruption events. We show with particle-in-cell simulations that pulsars can accelerate high-energy cosmic rays. We demonstrate that a population of millisecond pulsars located in the Galactic bulge can explain the di↵use gamma-ray emission observed by the HESS detector. Moreover, an extragalactic population of tidal disruptions by massive black holes powering relativistic jets can reproduce the spectrum and composition of UHECRs measured by the Auger experiment, but cannot produce the HE neutrinos detected by the IceCube experiment. Finally, we participate to the development of novel techniques that aim at detecting and reconstructing the properties of very-high-energy (VHE) neutrinos and UHECRs, in the context of the POEMMA and GRAND projects.À l’ère de l’astronomie des messagers multiples et des phénomènes transitoires, des perspectives nouvelles s’ouvrent pour l’étude des phénomènes les plus énergétiques de notre univers, et pour dévoiler l’origine mystérieuse des rayons cosmiques d’ultra-haute énergie (RCUHE) et des neutrinos de haute énergie (HE). Les rayons cosmiques sont des particules clés dans la production de rayonnement non thermique et, plus généralement, d’émissions multi-messagers. Dans cette thèse, nous développons plusieurs outils analytiques et numériques pour étudier l’accélération et les interactions des rayons cosmiques au sein des sources énergétiques. Les neutrinos HE attestant que de tels phénomènes sont à l’œuvre, nous étudions le caractère détectable de sursauts de neutrinos provenant de sources éphémères. Nous identifions alors deux catégories de sources intéressantes, les pulsars et les événements de rupture par effet de marée. Nous montrons, avec des simulations particulaires, que les pulsars peuvent accélérer des rayons cosmiques. Nous démontrons qu’une population de pulsars milli-secondes situés au centre de notre Galaxie peut expliquer l’émission diffuse en rayons gamma observée par le détecteur HESS. De plus, une population extragalactique d’événements de rupture par effet de marée produisant des jets relativistes peut expliquer le spectre et la composition des RCUHE mesurées par l’expérience Auger, mais ne peut pas produire les neutrinos HE détectés pas l’expérience IceCube. Enfin, nous participons au développement de techniques nouvelles visant à détecter et reconstruire les propriétés des neutrinos de très haute énergie et des RCUHE, dans le cadre des projets POEMMA et GRAND

Can we observe neutrino flares in coincidence with explosive transients?

International audienceThe new generation of powerful instruments is reaching sensitivities and temporal resolutions that will allow multi-messenger astronomy of explosive transient phenomena, with high-energy neutrinos as a central figure. We derive general criteria for the detectability of neutrinos from powerful transient sources for given instrument sensitivities. In practice, we provide the minimum photon flux necessary for neutrino detection based on two main observables: the bolometric luminosity and the time variability of the emission. This limit can be compared to the observations in specified wavelengths in order to target the most promising sources for follow-ups. Our criteria can also help distinguishing false associations of neutrino events with a flaring source. We find that relativistic transient sources such as high- and low-luminosity gamma-ray bursts (GRBs), blazar flares, tidal disruption events, and magnetar flares could be observed with IceCube, as they have a good chance to occur within a detectable distance. Of the nonrelativistic transient sources, only luminous supernovae appear as promising candidates. We caution that our criterion should not be directly applied to low-luminosity GRBs and type Ibc supernovae, as these objects could have hosted a choked GRB, leading to neutrino emission without a relevant counterpart radiation. We treat a set of concrete examples and show that several transients, some of which are being monitored by IceCube, are far from meeting the criterion for detectability (e.g., Crab flares or Swift J1644+57). Key words: astroparticle physics / neutrinos / gamma-ray burst: general / BL Lacertae objects: general / pulsars: general / supernovae: genera

Proton acceleration in pulsar magnetospheres

International audiencePulsars have been identified as good candidates for the acceleration of cosmic rays, up to ultra-high energies. However, a precise description of the acceleration processes at play is still to be established. Using 2D particle-in-cell simulations, we study proton acceleration in axisymmetric pulsar magnetospheres. Protons and electrons are extracted from the neutron star surface by the strong electric field induced by the rotation of the star, and electrons and positrons are produced in the magnetosphere through pair production process. As pair production has a crucial impact on electromagnetic fields, on gaps and thus on particle acceleration, we study its influence on the maximum energy and luminosity of protons escaping the magnetosphere. Protons are accelerated and escape in all our simulations. However, the acceleration sites are different for the protons and the pairs. As shown in previous studies, pairs are accelerated to their highest energies at the Y-point and in the equatorial current sheet, where magnetic reconnection plays an important role. In contrast, protons gain most of their kinetic energy below the light-cylinder radius within the separatrix current layers, but they are not confined within the equatorial current sheet. Their maximum Lorentz factors can reach 15% to 75% of the maximum Lorentz factor obtained by acceleration through the full vacuum potential drop from pole to equator, and increase with decreasing pair production. Their luminosity can reach 0.2% to 4% of the theoretical spin down luminosity of an aligned pulsar, and the minimum luminosity is obtained at the transition between the force-free and electrosphere regimes. These estimates support that millisecond pulsars could accelerate cosmic rays up to PeV energies and that new born millisecond pulsars could accelerate cosmic rays up to ultra-high energies.Key words: pulsars: general / acceleration of particles / methods: numerica

High-energy neutrino transients and the future of multi-messenger astronomy

International audienceThe recent discovery of high-energy astrophysical neutrinos and first hints of coincident electromagnetic and neutrino emission herald the beginning of the era of multi-messenger astronomy. Due to their high power, transient sources are expected to supply a significant fraction of the observed energetic astroparticles, through enhanced particle acceleration and interactions. Here, we review theoretical expectations of neutrino emission from transient astrophysical sources and the current and upcoming experimental landscape, highlighting the most promising channels for discovery and specifying their detectability