Search for Ultra-High-Energy Neutrinos from Gamma-Ray Bursts with the Pierre Auger Observatory
Abstract
Parallel talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/) Abstract: The Pierre Auger Observatory has excellent sensitivity to ultra-high-energy (UHE) neutrinos. The Surface Detector array is used to search for highly inclined neutrino-induced air showers, which, though not observed yet, have clear characteristic signatures. Due to the null observation of UHE neutrinos, we obtain upper luminosity limits on individual gamma-ray bursts from the public catalog GRBweb, that are in the field of view of the Observatory for neutrino searches. As the predicted neutrino luminosity from these sources strongly depends on the modeled emission mechanisms and dissipative processes, we obtain the limits using different neutrino spectra corresponding to distinct scenarios such as the one-zone fireball model. The spectra are calculated using the source code "Cosmic Ray Stochastic Interactions for Propagation" (CRISP), to compute quantities related to the propagation of heavier primaries within the source environment. Funded by the Bundesministerium für Forschung, Technologie und Raumfahrt; DAAD.
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Search for Ultra-High-Energy Neutrinos from Gamma-Ray Bursts with the Pierre Auger Observatory XXI Workshop on Neutrino Telescopes Therese Paulsen October 2, 2025
The Pierre Auger Observatory •Hybrid detector: Surface Detector (SD) and Fluorescence Telescopes •SD: 1660 water Cherenkov particle detector stations (WCD) spread over ≈3000 km2 •4Fluorescence Telescope sites, with 27 telescopes •For WCD: Detects Extensive Air Showers via secondary particles at ground •Recent AugerPrime upgrade enhances, i.e., composition sensitivity, but this analysis focuses on Phase I data CHAPTER 4 The Pierre Auger Observatory 0 10 20 30 40 50 60 70 80 [km] Coihueco HEAT Loma Amarilla Los Morados Los Leones Malargüe CLF XLF SD stations Figure 4.1: Layout of the Pierre Auger Observatory in Argentina. The black lines indicate the field of view of each telescope. Redone from [187]. 47 Figure made by Srijan Sehgal, Jannis Pawlowsky XXI Workshop on Neutrino Telescopes [email protected] 2 /14
Neutrino detection principle Inclined neutrino-induced air showers can contain a significant electromagnetic component at ground −for CR, only the muonic part reaches the ground Figure made by Michael Schimp XXI Workshop on Neutrino Telescopes [email protected] 3 /14
Effective area for neutrino detection Instantaneous effective areas as a function of θ(left) and Eν(right) 60 65 70 75 80 85 90 95 (deg) 10 5 10 4 10 3 10 2 10 1 100 Effective area (km2) Auger ES , E = 1019 eV Auger ES , E = 1018 eV Auger DGH, e CC, E = 1019 eV Auger DGH, e CC, E = 1018 eV Auger DGL, e CC, E = 1019 eV Auger DGL, e CC, E = 1018 eV 1013 1014 1015 1016 1017 1018 1019 1020 E (eV) 10 5 10 4 10 3 10 2 10 1 100 Effective area (km2) Auger ES , = 91 o Auger ES , = 92 o Auger ES , = 93 o Auger DGH e CC, = 75 o Auger DGH e CC, = 80 o Auger DGH e CC, = 85 o Auger DGL e CC, = 60 o Auger DGL e CC, = 66 o Auger DGL e CC, = 69 o IceCube CC, [30 o , 90 o ] IceCube CC, [ 5 o , 30 o ] IceCube CC, [ 30 o , 5 o ] IceCube CC, [ 90 o , 30 o ] Source: JCAP 11 (2019) 004 XXI Workshop on Neutrino Telescopes [email protected] 4 /14
Fluence limits of GRB170817A •Upper limits on the neutrino fluence for Auger, IceCube, and ANTARES, for two different periods around the event, upper panel ±500 s, lower panel 14 days •We want to compute the upper limit of this source, among others, using other neutrino emission spectra Source: A. Albert et al 2017 XXI Workshop on Neutrino Telescopes [email protected] 5 /14
Constrains in the UHEνemission from GRBs •Due to the current null observation of UHEν, we want to study the upper fluence limits from GRBs •In general, we have that, for a specific neutrino emission model, Nν=Z Z ϕMODEL ν(Eν)Aeff(Eν, θ(t),t)dEνdt. F(Eν)=E2 ν Nup νϕMODEL νT90 REmax Emin RT90 0ϕMODEL νAeff(Eν, θ(t),t)dtdE. •Using a 90%C.L limit with the Feldmann-Cousins approach for 0background and 0 signal, where Nup =2.44 events are expected •In the case of ϕMODEL ν∝E−2,90%of the expected detected events at the Observatory are between 100 PeV and 25 EeV XXI Workshop on Neutrino Telescopes [email protected] 6 /14
Gamma-ray bursts (GRBs) •Schematic view of a GRB, showing a collimated jet containing shells of different speeds, colliding shells, responsible for the gamma-ray emission (Internal shock model) Credit: NASA/Goddard Space Flight Center/ICRAR XXI Workshop on Neutrino Telescopes [email protected] 7 /14
Luminosity limits using detailed simulation of neutrino emission spectrum 1041061081010 Energy[GeV] 10−13 10−11 10−9 10−7 10−5 E2Fν[GeV/cm2] IS PHOTO ICMART Auger sensitive area •Three of the spectra are taken from De Lia and Tamborra, JCAP10(2024)054 — Internal Shock (IS) — Photospheric (PH) — Internal-collision-induced magnetic reconnection and turbulence (ICMART) •Iron primary, photodisintegrate to protons in the source environment •Modeled using so-called standard parameters XXI Workshop on Neutrino Telescopes [email protected] 8 /14
Redshift estimation •As the redshift is only known for z∼16%of the sample, we need a procedure to estimate this value →create distribution using Kernal density estimation (KDE) Source:PoS(ICRC2025)1093 XXI Workshop on Neutrino Telescopes [email protected] 9 /14
References for the neutrino spectral shapes •Following the publication by Valentin De Lia and Irene Tamborra 1, we look at three different GRB models: Internal shock (IS), Photospheric model (PHOTO) and Internal-collision-induced magnetic reconnection and turbulence (ICMART) —ϵd:Energy fraction dissipated in acceleration —ϵX:Energy fraction that effectively accelerates seed particles —ϵB:Fraction of energy that contributes to amplify the magnetic field —k:Spectral index of primary particle 1JCAP10(2024)054 XXI Workshop on Neutrino Telescopes [email protected] Backup slides
Dependence of the neutrino fluence on Γ •Using the ”standard parameters”, varying the Lorentz factor of the jet •Some of this parameter space for IS and PHOTO models cannot be probed by Auger (Γ∈[10 −80)) JCAP10(2024)054 1041051061071081091010 E(GeV) 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 E2 Fµ+¯ µ(cm2GeV) IS 1041051061071081091010 E(GeV) PHOTO 1041051061071081091010 E(GeV) ICMART 101 102 103 1041051061071081091010 E(GeV) 102 101 100 101 FFe µ+¯ µ/Fp µ+¯ µ IS 1041051061071081091010 E(GeV) PHOTO 1041051061071081091010 E(GeV) ICMART 101 102 103 Figure 7. Same as figure 6, but for investigating the dependence of the neutrino fluence on ( k =2 . 2 is fixed for both the internal shock and the photospheric models, while k =2 . 0is used for the ICMART case). Decreasing increases the neutrino fluence, with the larger spread occurring for the internal shock and photospheric jet models. In fact, for these models, the interaction radius scales as 2 , which implies that for larger , internal shocks happen at a radius where both photon and seed nuclei have lower densities. However, this is not the case for the ICMART model, for which the radius of interaction is independent of the bulk Lorentz factor. This explains the milder variation of the neutrino fluence on in the internal shock model. A strong variation of the neutrino fluence as a function of occurs according to the composition. happen at a nearly constant radius). This explains the milder dependence of the neutrino fluence on in the internal shock model. The energy corresponding to the maximum neutrino fluence ( EM ‹ ) is strongly shifted to lower energies as decreases; this is because higher photon densities are achieved as decreases, hence the photodisintegration timescale increases and crosses the acceleration timescale at lower energies. This implies that the cutoffenergy of the parent spectrum decreases, which also forces the neutrino fluence to peak at lower energies. This effect is less prominent in Poynting-flux jets than in kinetically-dominated jets since the acceleration process is more efficient in the former thanks to the larger magnetic fields. The bottom panels of figure 7also highlight a strong variation of the neutrino fluence as a function of according to the composition. The ratio between the neutrino fluence of – 20 – Source: JCAP10(2024)054 XXI Workshop on Neutrino Telescopes [email protected] Backup slides
Dependence of the neutrino fluence on the spectral index •Using the standard parameters, varying the spectral index of the injected parent nucleus •Smaller spectral index →larger neutrino fluence JCAP10(2024)054 1041051061071081091010 E(GeV) 1014 1013 1012 1011 1010 109 108 107 106 105 104 103 E2 Fµ+¯ µ(cm2GeV) IS 1041051061071081091010 E(GeV) PHOTO 1041051061071081091010 E(GeV) ICMART 2.0 2.2 2.4 2.6 2.8 3.0 k 1041051061071081091010 E(GeV) 102 101 100 101 FFe µ+¯ µ/Fp µ+¯ µ IS 1041051061071081091010 E(GeV) PHOTO 1041051061071081091010 E(GeV) ICMART 2.0 2.2 2.4 2.6 2.8 3.0 k Figure 6. Dependence of the neutrino fluence on the injection spectral index of the accelerated parent nucleus/nucleon spectra. Top: ‹µ + ¯‹µ neutrino fluence as a function of the neutrino energy for k =2 . 0–3 . 0, using our benchmark Fe-jet (cf. table 1) for the internal shock, photospheric, and ICMART jet models; the other jet parameters are defined as in table 1, in particular = 300 is fixed. Bottom: Ratio between the Fe-jet neutrino fluence and the p -jet one as a function of the neutrino energy. A smaller k allows for a larger neutrino fluence, because it favors larger densities of seed nuclei; such trend holds independent of the jet composition. table 1. Decreasing the power law index tends to increase the neutrino fluence, because it allows for a larger fraction of the total population to be accelerated at high energies. We can also note that decreasing k slightly increases the energy EM ‹ corresponding to the maximum neutrino fluence. For our benchmark jet, we also observe that k mostly scales the neutrino fluence in a similar fashion for p - and Fe-jets, as evident from the bottom panels of figure 6. Figure 7explores the impact of on the neutrino emission. For fixed composition, from the top panels of figure 7, we can see that decreasing tends to increase the neutrino fluence, in a way that depends on the jet model. For the internal shock and photospheric models, changes in affect the radius of interaction ( RIS = 2 2c˜ tvar ); when decreases, internal shocks happen at a radius where both photon and seed nuclei have larger densities. However, this is not the case for the ICMART model, for which the radius of interaction is independent of the bulk Lorentz factor (internal shocks trigger magnetic reconnection events assumed to – 19 – Source: JCAP10(2024)054 XXI Workshop on Neutrino Telescopes [email protected] Backup slides