Production of High-Energy and Ultrahigh-Energy Neutrinos
Kohta Murase (Penn State) November 30 Snowmass 2021 All-Sky Neutrino Spectrum & Flavors
2 -8 -2 -1 -1 All-sky n flux per flavor En Fn ~ 10 GeV cm s sr at En ~200 TeV Flavor ratio consistent with ne:nµ:nt ~ 1:1:1
possible structure?
cutoff? - 9.5-yr upgoing nµ “track” s=2.28+0.08-0.09 - 6-yr “shower/cascade” s=2.53+-0.07 IceCube Collaboration @ Neutrino 2020 IceCube Collaboration 20 PRL arXiv:2008.04323 Multi-Messenger Astro-Particle “Backgrounds”
gamma neutrino UHECR
unresolved
Energy generation rate densities of 3 messengers are all comparable (e.g., KM & Fukugita 19 PRD) High-Energy Neutrino Sky
upgoing tracks starting events
consistent w. isotropic distribution/extragalactic origins IceCube Point Source Searches
IceCube Collaboration 20 PRL starburst galaxy/AGN
NGC 1068 TXS 0506+056 PKS 1414+240 GB6 J1542+6129 Jetted AGN (blazar)
“Catches” (~3s) exist but none have reached the discovery level Key questions
What we know: 2 -8 -2 -1 -1 - En Fn ~ 10 GeV cm s sr , Flavor ratio is consistent w. 1:1:1 - Energy budget: comparable to those of g rays & UHECRs - A few sources w. ~3s (NGC 1068 & TXS 0506+056)
Key (astrophysical) questions we would like to reveal: • What is the main sources of IceCube neutrinos? • What is the connection to the sources of g rays and UHECRs? • How does the n spectrum extend & Is there a structure? • What is the mechanism of n production (pp or pg or…)? • Can we expect neutrinos coinciding with gravitational waves? • How can we use ns to probe astrophysical phenomena? • How much is the Galactic contribution? 8
1 2 2 1 2 3 2 2 = ⌦ BpR ✓0/c ⌦ BpR ✓0/c (67) 2 ⇤ ⇤ ⇠ 2 ⇤ ⇤
6.6 1012 V (68) ⇥
E 2 1 E0 0.05E0 0.8 PeV (E0 /1 keV) (70) ⌫ ⇡ p ' 1 s ' (71) 2 ↵ 1 (72) ⇠ 2 (0 1) (73) ⇠ High-Energy 2Neutrino↵ 2.3 Production (74) ⇠ Cosmic-ray Accelerators Cosmic-ray Reservoirs Starburst galaxy Galaxy cluster Active galaxy g-ray burst 2 2 (75) accretion to core-collapse of ⇠ high star-formation gigantic reservoirs w. massive black hole massive stars → many supernovae AGN, galaxy mergers s resonance spp pg + spg~aspp~0.5 mbp + n + ⇡ (76) ! weak energy dependence ε'pε’γ ~ (0.34 GeV)(mp/2) ~ 0.16 GeV2 spp~30 mb p + N⇡ + X (77) ! p +γ → Nπ + X p + p → Nπ + X ⇡± ⌫ +¯⌫ + ⌫ (or⌫ ¯ )+e± (78) ! µ µ e e 2 c dz dH E⌫ ⌫ = [ns"⌫ L"⌫ ] n0L⌫ (79) 4⇡ (1 + z)2H(z) / 4⇡ Z (0.4 0.6) (80) p ⇠ 0.2 (81) p ⇠ L L lw (82) ⌫ / High-Energy Neutrino Production Cosmic-ray Accelerators Cosmic-ray Reservoirs Starburst galaxy Galaxy cluster Active galaxy g-ray burst accretion to core-collapse of high star-formation gigantic reservoirs w. massive black hole massive stars → many supernovae AGN, galaxy mergers relativistic outflow ex. shocks in outflow → electron acceleration e+ µ → synchrotron emission + target gas nµ p+ nµ ne CR p e+ n p ne CR e e+ + CR accelerator target g µ n CR confinement + µ p n n CR p e+ µ e magnetized “environments” n p ne High-Energy Neutrino Production Cosmic-ray Accelerators Cosmic-ray Reservoirs Starburst galaxy Galaxy cluster Active galaxy g-ray burst accretion to core-collapse of high star-formation gigantic reservoirs w. massive black hole massive stars → many supernovae AGN, galaxy mergers relativistic outflow ex. shocks in outflow → electron acceleration e+ µ → synchrotron emission + target gas nµ p+ nµ ne CR p e+ n p ne CR e e+ + CR accelerator target g µ n CR confinement + µ p n n CR p e+ µ e magnetized “environments” n p ne 3 2 2−p olate the local 1.4 GHz energy production rate per unit neutrino spectrum would be, Eν Φνµ ∝ Eν .Theenergy volume (of which a dominant fraction is produced in qui- distribution of cosmic-ray protons measured on Earth fol- −2.75 No. 2, 2008 COSMICescent spiral RAYS galaxies) AND NEUTRINOSto the redshifts FROM where most CLUSTERS of the OFlows GALAXIES a power-law dN/dE ∝ E up L107 to the ”knee” in stars had formed through the starburst mode, based on the cosmic-ray spectrum at a few times 1015 eV [23, 25]. the observed redshift evolution of the cosmic star forma- (The proton spectrum becomes steeper, i.e. softer, at tion rate [24], and calculate the resulting neutrino back- higher energies [2].) Given the energy dependence of the ground. The cumulative GeV neutrino background from confinement time, ∝ E−s [22], this implies a produc- starburst galaxies is then tion spectrum dN/dE ∝ E−p with p =2.75 − s ≈ 2.15. This power-law index is close to, but somewhat higher IceCube c E2Φ (E =1GeV)≈ ζt [4ν(dL /dV )] than, the theoretical value p =2,whichimpliesequal ν ν ν 4π H ν ν=1.4GHz IceCube −7 −2 −1 −1 energy per logarithmic particle energy bin, obtained for =10 ζ0.5 GeV cm s sr . (2) Fermi acceleration in strong shocks under the test par- ticle approximation [26]. We note that the cosmic-ray Here, t is the age of the Universe, and the factor H spectrum observed on Earth may not be representative ζ =100.5ζ incorporates a correction due to redshift 0.5 of the cosmic-ray distribution in the Galaxy in general. evolution of the star formation rate relative to its present- galaxy group/clusterThe inferred excess relative to model predictions of the day value. The value of ζ ∼ 1appliestoactivitythat 0.5 > 1GeVphotonfluxfromtheinnerGalaxy,impliesthat traces the cosmic star formation history [6]. Note that the cosmic-rays are generated with a spectral index p Koteraflavor, Allard, oscillationsKM, Aoi, wouldDubois, convert the pion decay flavor ra- smaller than the value p =2.15 inferred from the local Pierogtio, &ν Nagataki: ν : ν 09=1:2:0to1:1:1[11],sothat ApJ KM, Inoue & Nagataki 08 ApJ e µ τ cosmic-ray distribution, and possibly that the spectral Φ = Φ = Φ = Φ /2. νe νµ ντ ν index of cosmic-rays in the inner Galaxy is smaller than the local one [27]. The spectrum of electrons accelerated −5 10 in SNe is inferred to be a power law with spectral index Fig. 1.—Expected event rates for muon neutrinos (nmmϩ n¯ ) in IceCube-like p =2.1 ± 0.1overawiderangeenergies,∼ 1GeVto starburst galaxyFig. 2.—Cumulative neutrino (neeϩ n¯¯¯ϩ nmmttϩ n ϩ n ϩ n ) background from detectors from five nearby CGs: Virgo, Centaurus, Perseus, Coma, and Oph- ∼ 10 TeV, based on radio, X-ray and TeV observations CGs for broken power-law>0.1 CR spectra PeV withpIceCube12p 2.0 andp p 2.4data: . The break −6 p p p 17.5 16.5 iuchus. Broken power-law CR spectra with10 p122.0 ,p 2.4 , and b p (e.g. [28]). p 17.5 energies arebb10 eV (thick lines) and 10 eV (thin lines), re- AMANDA(νp); Baikal(ν ) 245Ϫ3 10 eV is assumed, and the isobaric model withXCR µ 0.029 ise used. Note spectively. The CR powerconsistent isFor normalized a steeply to falling ( dnw.˙/d proton) earlierp 2 # spectrum10 erg Mpc such as dN/dE ∼ s sr] 1 18 that IceCube and KM3NeT mainly cover2 the northern and southern celestial Ϫ −2 yr at p 10 eV, as requiredE ,theproductionofneutrinosofenergy to account for CRs above the second knee. Eν is domi- hemispheres, respectively. Neutrino oscillation is taken into account. [See the For the isobaric model,theoretical the correspondingX predictions is 0.029 and 0.067. For the −7 nated by protonsCR of energy E ≈ 20Eν [18], so that the electronic edition of the Journal for a color10 version of this figure.] central-AGN model, Kolmogorov-like turbulence is assumed with k p WB Bound cosmic-ray ”knee” corresponds to E ∼CG0.1PeV.Inanal- IceCube 30 2 Ϫ1 p p p ν [GeV/cm 10 cm s . We taketdynDt 1 Gyr andz max 2 . WB represents the ν Star Bursts ogy with the Galactic injection parameters of cosmic- Φ Waxman-Bahcall bounds (Waxman & Bahcall 1998). culations of the neutrino spectra using formulae based on the 2 2 ν 0.1 km rays, we expect the neutrino background to scale as E −8 SIBYLL code at high energies (Kelner10 et al. 2006). 2 SB −7 −0.15±0.1 −2 −1 −1 The neutrino and gamma-ray fluxes can be estimated via the where CGs are assumedEν Φν to≈ be10 the( mainEν /1GeV) sources of CRsGeV from cm s sr (3) Atmospheric→ 2 the second knee to the ankle. Here,n (0) is the local density effective optical depth for the pp reaction as fpp1 km ← GZK up to ∼ 0.1PeV.Infact,the”knee”intheprotonspec-CG −9 Loeb & Waxman 06 JCAP≈ 0.8jppnct N int, where nN is the target10 nucleon density in the ICM, of massive CGs andfz is a correction factor for the source 3 5 7 9 11 trum for starburst galaxies may occur at an energy higher 10 10 10 evolution10 (Murase10 2007; Waxman & Bahcall 1998). For de- jpp is the pp cross section, and tint tdyn or max(r/c , tdiff)E is [GeV] the than in the Galaxy. The steepening (softening) of the ∼ Ϫ4.5 Ϫ3 ν pp interaction time. BecausenN 10 cm atr 1.5 Mpc tailed numerical calculationsproton spectrum of the background, at the knee we may treat be more either due to a ∼ ∼ distant CGs following Colafrancesco & Blasi (1998) adopting (Colafrancesco & Blasi 1998;FIG. Pfrommer 1: The shaded & Enßlin region brackets 2004), the range of plausible steeper proton production spectrum at higher energies, or k 0.6,andj 10Ϫ25 cm 2 inthe100PeVrange(Kelner the mass function ofafasterdeclinewithenergyfortheprotonconfinement Jenkins et al. (2001). The results for the pp∼ pp ∼ choices for the spectrum of the neutrino background. Its up- et al. 2006), we obtain per boundary is obtained for a power-lawbroken index p power-law=2of casetime. are Since shown both in the Figure acceleration 2. With of protonsb p and their the injected cosmic-rays, and its lower boundary17.5 corresponds confinement depend on the magnetic field, we expect the 14.5 10 eV, the expected event rates above 0.1 PeV in IceCube p . Eν < Ϫ1 Ϫ1 Ϫto3 =225 for 10 eV. The solid(Ahrens green line et al.corre- 2004)”knee” are 2 yr to shiftfor to model a higher A, energy1 yr infor starbursts, model where the fpp2.4 # 10 n N,Ϫ4.5(t int /1 Gyr).p . (1) ∼ sponds to the likely value =215 (see text).B, Other5 yr lines:Ϫ1 for the the isobaricmagnetic∼ model, field is and much3 stronger yr∼Ϫ1 for thanthe central the Galactic value. WB upper bound on the high energy muon neutrino∼ intensity The predicted neutrino∼ intensity is shown as a solid line from optically-thin sources; the neutrino intensityAGN model. expected Roughly speaking, high-energy neutrinos from charged-pion in Fig. 1. The shaded region illustrating the range of from interaction with CMB photons (GZK); theHence, atmospheric upcoming telescopes may be able to find multi-PeV decay have typical energy 0.03 (true only in the average uncertainty in the predicted neutrino background. This n neutrino∼ background; experimental upperneutrino bounds of signals optical from CGs, providing a crucial test of our sce- sense, because charged particlesCerenkov have wide experiments energy distributions (BAIKAL [29] and AMANDA [30]); range is bounded from above by the intensity obtained and the expected sensitivity of 0.1 km2 andnario. 1 km From2 optical equationfor (2),p =2,correspondingtoequalprotonenergyperlog- we can also estimate the correspond- and high multiplicities as expected from the KNO scaling law) 02 Cerenkovտ detectors [1]. ing gamma-ray backgroundarithmic from bin, andp decay,from below which by is theggF intensity obtained (Kelner et al. 2006). Hence, neutrinos PeV are directly related Ϫ9 Ϫ8 Ϫ2 Ϫ1 Ϫ1 ∼ to CRs above the second knee. (10 to 10 ) GeVfor cmp =2 s.25, sr correspondingfor the broken to power-law the lower value of the First we obtain numerically theEquation neutrino (2) spectra provides and expected an estimate ofcase. the This GeV is neu- only (0.1–1)%confinement of time the EGRET spectral limit, index, consistents =0.5. event rates from five nearbytrino CGs, background. utilizing the Theb extrapolationmodel or ofwith this background the nondetectionThe so far extension for individual of the CGs. neutrino Note spectrum that the to energies to higher neutrino energies depends on the energy spec- E > 1PeVishighlyuncertain.Ifthesteepeningofthe double-b model description in Tables 1 and 2 in Pfrommer & expected gamma-ray backgroundν flux would increase ifb can trum of the high energy protons. If the protonbe decreased, energy dis- requiringproton larger spectrum CR power at the from knee CGs. is due to a rapid decrease Enßlin (2004) for the thermaltribution gas profile follows of each a power-law, CG (Fig.dN/dE 1). ∝ E−p,thenthe in the proton confinement time within the Galaxy rather Our gamma-ray fluxes for single power-law spectra agree with the results of Pfrommer & Enßlin (2004). As is apparent in 4. IMPLICATIONS AND DISCUSSION Figure 1, the detection of neutrino signals from individual CGs To test the CG origin of second knee CRs, high-energy neu- could be challenging even for nearby objects. It may be achiev- trinos should offer one of the most crucial multimessenger able, however, through a detailed stacking analysis. signals. Unlike at the highest energies, CRs themselves in the More promising would be the cumulative background signal. 1018 eV range offer no chance of source identification as they A rough estimate of the neutrino background is (e.g., Murase should be severely deflected by Galactic and extragalactic mag- 2007; Waxman & Bahcall 1998) netic fields. Moreover, due to magnetic horizon effects, extra- galactic CRs Շ1017 eV may not reach us at all (Lemoine 2005; 22c 1 dN Kotera & Lemoine 2007) so even the broken power-law spectral nnF min (1, fpp) nCG(0)fz ∼ 4pH0 3 d dt form will not be directly observable. Gamma-rays are unaf- fected by intervening magnetic fields, but those at տPeV en- Ϫ9 Ϫ2 Ϫ1 Ϫ1 1.5 # 10 GeV cm s sr fz ergies relevant for the second knee are significantly attenuated ∼ by pair-creation processes with the CMB and cosmic IR back- f ( p 1018 eV) Ϫpϩ2.1 # pp n , (2) grounds (e.g., Kachelrieß 2008). In contrast, neutrinos in the []2.4 # 10Ϫ3 () 10 PeV PeV–EeV energy range should be unscathed during propaga- tion (Bhattacharjee & Sigl 2000 and references there in). Con- High-Energy Astro-Particle “Grand-Unification” First demonstration of the “unification” scenario with a concrete astrophysical model UHECR cosmogenic Fang & KM 18 Nature Phys. • Jetted AGN as “UHECR” accelerators & galaxy clusters/groups as environments • low-energy: confinement in reservoir environments • high-energy: escaping nuclei → “hard” spectrum • Prediction: smooth transition from source neutrinos to cosmogenic neutrinos Extremely High-Energy Neutrinos above 3 PeV RNO-G Collaboration 2020 • Source ns can dominate over cosmogenic ns (in the mixed composition) • Spectral extension of IceCube ns is a key: break? cutoff? hardening? 2 -9 -2 -1 -1 • Target sensitivity: En Fn~3x10 GeV cm s sr (e.g., KM & Beacom 10 PRD) Medium-Energy Neutrinos below 30 TeV • 10-100 TeV shower data: large fluxes of ~10-7 GeV cm-2 s-1 sr-1 -5 10 KM, Guetta & Ahlers 16 PRL pp () pp () see also ] minimal p ( ) KM, Ahlers & Lacki 13 PRDR -1 -6 minimal p () Capanema, Esmaili & KM 20 PRD sr 10 Capanema, Esmaili & Sepico 20 -1 s Fermi shower data -2 source-independent -7 10 IceCube “generic” n spectra considered [GeV cm track 2 10-8 non-blazar EGB data E 10-9 100 101 102 103 104 105 106 107 108 E [GeV] Fermi diffuse g-ray bkg. is violated (>3s) if n sources are g-ray transparent → existence of “hidden (i.e., g-ray opaque) neutrino sources” (n data above 100 TeV can be explained by g-ray transparent sources) Multimessenger Emission from AGN Coronae & Disks corona/RIAF disk: hot, collisionless plasma magnetic reconnections & turbulence -> proton acceleration is promising KM, Kimura & Meszaros 20 PRL Kimura, KM & Meszaros 19 PRD Kimura, KM & Meszaros 20 • Both pp & pg interactions in coronae contribute to 10-100 TeV n emission • Intra-source g-ray cascades -> robust prediction of MeV g-ray counterparts High-Energy Neutrinos from Nearby (Non-Jetted) AGN KM, Kimura & Meszaros 20 PRL 10-6 NGC 1068 43 LX=10 erg/s Cascade d=12.7 Mpc Thermal e X 10-7 ] -1 s IceCube -2 eASTROGAM 10-8 Promising nearby sources AMEGO starburst [GeV cm -9 1. Circinus Galaxy 10 (MW16) E Fermi LAT 2. ESO-G001 E F -10 HESS 3. NGC 7582 10 4. Cen A 5. NGC 1068 10-11 6. NGC 424 10-410-310-210-1 10 0 101 102 103 104 105 106 107 7. CGCG 164-019 E [GeV] • NGC 1068: predicted to be a g-ray hidden, the brightest n source in the northern sky • More bright sources in the southern sky (testable w. KM3Net) Need n detectors sensitive to 1-10 TeV ns with better angular resolutions REVIEWS Box 1 | Multi- messengers and their interrelations A multi-messenger source might emit two, three or even all four different For single objects, even those of extreme mass and undergoing types of messengers. From a binary neutron star merger (panel a of the substantial accretion, relatively weak GW emission is expected as the figure), such as the GW/GRB 170817 event, two types of multi- messengers, time- varying quadrupole moment (which requires the breaking of gravitational waves (GW) and photons (γ), were observed54,57,59, the latter azimuthal symmetry) is thought to be small in these cases. The sole indicating that the source was a short gamma-ray burst (GRB). Such sources exception would be an engine- driven supernova, or a plain supernova, may also emit high-energy neutrinos (HENs) and cosmic rays (CRs)84,85,168, located in our galaxy (panels e and f of the figure), which would be although for the GW/GRB 170817 event, theories predict such fluxes to be sufficiently close such that the detection of coherent or incoherent too low for current detectors. If this is true, it will take closer binary neutron GWs by current and future ground- based detectors is anticipated. star merger events or next- generation HEN facilities to observe HENs from IceCube is well equipped for detecting thermal (~10 MeV) neutrinos these sources. The so-called long GRBs (panel b of the figure) also may emit from such galactic supernovae. A challenge for theory is to predict the HENs and CRs, which so far have not been detected, while their GW amplitude and spectrum of the GW and neutrinos from different types emission is expected to be very low. of supernovae. Another example is a tidal disruption event (TDE) of a star by a massive Strong GW emissions have been observed from the mergers of compact black hole (panel c of the figure). In this case, shocks in the disrupted gas binary systems, either from two merging stellar mass black holes (panel g can accelerate particles and lead to CRs and HENs169–172. TDEs involving of the figure)27, two merging neutron stars (panel a)54 or black hole–neutron white dwarf stars and ~104 M (where M is solar mass) black holes lead to star mergers, because the final inspiral to coalescence yields a strong GW ⊙ ⊙ strong low-frequency (~1 mHz) GW emission that could be observed by the signal in the ‘sweet spot’ frequency range for ground- based GW detectors. forthcoming evolved Laser Interferometer Space Antenna (eLISA) mission. In the case of 30 M 30 M black hole binary systems, such coalescence ⊙ + ⊙ A solitary supermassive black hole with a jet may emit γ- rays, HEN and CRs events can already be observed out to ~500 Mpc distances141. However, in (panel d of the figure), as it is suspected in the case of the 2017 flaring the case of black hole–black hole mergers little electromagnetic (EM) flux episode of the BL Lac- type blazar TXS 0506+056 (REFS65–68,71,72). is expected, because the ambient matter density (protons, electrons) in the In general, in compact mergers, TDEs and related sources, the co- vicinity of the binary, at the time of the merger, is typically very low. A key High-Energyproduction of CRs, HEN andNeutrino high-energy γ- rays is anticipated, Transients: as the exception are accreting Many supermassive black Targets holes at the centres of massive physics of these three messengers are closely connected: shocks and galaxies, which are expected to merge in the wake of the coalescence of the high-energy particle acceleration lead to the interaction of highly their component galaxies. These supermassive black holes mergers are relativistic protons (or nuclei) with ambient gas or intense radiation fields, key targets for the eLISA mission, and may well exhibit accompanying EM, pointing resulting& timing in neutrinos, γ- rays →and electrons/positrons.good chance toCR and discoverHEN emission173. n sources a Short γ-ray burst neutron star merger b Long γ-ray burst c Tidal disruption event ν, γν, γ ν, γ CR CR CR ,( Neutron ν γ) Star star GW Progenitor GW Ejecta d Blazar flare ν, γ e Engine-driven supernova ν CR Jet Wind Dust torus ν,(γ) ν, γ Disk Choked jet ν, γ f Supernova , g Double black hole merger ν γ CR GW Black GW hole Wind ν, γ KM & Bartos 19 ANRPS Meszaros, Fox, Hanna & KM Circumstellar Nature Rev. Phys. 19 material Gas Figure adapted with permission from REF.174, Annual Reviews. NATURE REVIEWS | PHYSICS VOLUME 1 | OCTOBER 2019 | 587 Blazar Flares: Challenges of TXS 0506+056 2017 multimessenger flare 2014-2015 neutrino flare The Astrophysical Journal, 891:115 (16ppKeivani), 2020, MarchKM et 10 al. 18 ApJ Petropoulou, KM etPetropoulou al. 20 ApJ et al. 47 We next discuss a few caveats that should be kept in mind 10 (max) LM Lp when interpreting10−10 our predictions(max) for the long-term neutrino 2× Lp g:Fermi-LAT IceCube-170922A IceCube emission of TXSopt: Swift0506-UVOT/X+056.-Shooter opt: ASAS-SN 1. The predictions rely on the assumption that the maximal 1046 n neutrino flux obtained for each epoch is representative of X:Swift-BAT ] −11 1 10 − the long-term neutrino emission of the source. Ideally, ] s X:MAXI 1 2 fi − − one should nd a scaling relation between the maximal neutrino flux and the photon flux in some energy band 1045 g:Fermi-LAT [erg s with continuous temporal coverage, and then use the ε [erg cm L ε −12 10 ε long-term light curve to compute the predicted number of F n ε muon neutrinos (X:Swifte.g., Petropoulou-XRT/NuSTAR et al. 2016). Although the 0.1–300 GeV energy band of Fermi is ideal for this 1044 purpose, we cannot establish a robust relation between ()max−13 F10 and Fγ, as shown in Figure 3 (left panel). In nn+ ¯ −12 contrast, we10 find that the X-ray flux is a better probe of the maximal neutrino103 flux104 within105 our model, with 1043 FF()max µ (right panel of Figure 3). This is partly nn+ ¯ X 100 105 1010 1015 because the SED has a valley inε [eV] the X-ray range, which is the mostsee also important KM, Oikonomou for constraining& Petropoulou hadronic compo-18, Ansoldi+Figure 18, Cerutti 4. Same as+ in19, Figure Gao+2,butforacasewherethemodel-predictedneutrino 19, Rodriguez+ 19, Reimer+ 19 nents. The X-ray coverage of the source before the 2017 flux is compatible with the IceCube flux of epoch 4. Here, we assume 7 48 −1 flare is very sparse (see Figure 1), thus preventing a more Text¢ =´210K (or, equivalently, ¢ext 5 keV) and Lp¢ =´1.7 10 erg s . sophisticated- g-ray cascades analysis than theplace one presented stringent here. boundsAll → otherchallenging parameters are the samesingle as those listed-zone in Table models8 for epoch 4. 2. We- other cannot coincidences… exclude the possibility 3HSP that the J095507.9, physical PKS 1502+106, AT2019dsg (TDE) properties of the jet change drastically in between the four epochsNeed we more chose for follow our analysis.-up Such campaigns changes in the jet and/ordata bylarger a factor statistics of ∼10. In addition, in n thisdata case is unlikely in parameters could happen in highly variable blazars(e.g., astrophysical view, for it requiresahighlysuper-Eddingtonproton Raiteri et al. 2013; Ahnen et al. 2017). This limitation power to account for the low photomeson production efficiency. stems from the lack of quasi-simultaneous multi-wave- Given the unprecedented neutrino flux measured by IceCube length data for long-time windows and highlights the in 2014–2015, one could still argue that the conditions in the need for X-ray monitoring of blazars. blazar zone were significantly different compared to other 3. The SEDs we constructed are not contemporaneous. epochs. We therefore explored this possibility by performing a More specifically, the X-ray spectra are computed from wide scan of the parameter space for one-zone models. Our individual Swift-XRT observations of duration of a methodology and results are presented in the Appendix. We few kiloseconds each, while the gamma-ray spectrum found no parameter set for the blazar zone that can is averaged over the whole epoch of interest (∼0.5 yr). simultaneously explain the neutrino flare and be compatible In this regard, the Swift-XRT observations are instanta- with the electromagnetic constraints. Moreover, all cases neous compared to the selected time window. So, require a highly super-Eddington jet power, namely 23 47 9 −1 when we translate the maximal neutrino flux, which is (10–) 10 LEdd, where LEdd 1.3´ 10(MM 10 ) erg s mainly set by the X-ray flux, into an expected number of is the Eddington luminosity of a black hole with mass M. The events and use DT = 0.5 yr as the typical duration, we necessary proton power could be reduced to Eddington levels if may overestimate the numberofneutrinos.TheX-ray the energy density of the external photon field (in the blazar flux variability within epoch 2, for example, can lead zone) was two or three orders of magnitude higher than all to an overestimation of the neutrino number by a factor other epochs(see also Reimer et al. 2019). of ∼2. We therefore conclude that the high neutrino flux of epoch 4 cannot be explained concurrently with the electromagnetic data if both emissions originate from the same region, in agreement 5.2. Implications for the 2014–2015 Neutrino Flare with previous studies (Murase et al. 2018; Reimer et al. 2019; Here, we focus on the implications of our model for the Rodrigues et al. 2019). 2014–2015 neutrino flare. As an illustrative example, we show in Figure 4 acasewherethemodel-predictedneutrinoflux is 6. Discussion compatible with the IceCube flux of epoch 4. The parameters are 6.1. Remarks on the Maximal Neutrino Flux and Proton the same as those listed in Table 8,exceptforthecharacteristic Luminosity external photon energy (temperature) and the proton luminosity, which now read ¢ 5 keV (T¢ =´2 107 K) and L¢ = We have constrained the maximal neutrino flux (F()max ) and ext ext p nn+ ¯ 48 −1 ()max 1.7´ 10 erg s ,respectively.Fortheadoptedparameters, the required proton luminosity (Lp ), assuming that the low- the electromagnetic emission of the secondaries produced via energy hump in the SED is attributed to synchrotron emission photohadronic interactions and photon–photon pair production from primary electrons. This assumption is plausible and --- reaches a flux of ~´(–3 10 ) 1011 erg cm 2 s 1,which widely accepted. Indeed, the optical-to-soft X-ray data can be confirms the analytical results of Murase et al. (2018).Suchhigh fitted with a single power law, especially evident in epoch 2 X-ray and gamma-ray fluxes clearly overshoot the MAXI and and in the 2017 flare(Keivani et al. 2018). It is therefore Swift-BAT upper limits by a factor of ∼2–3andtheFermi-LAT unlikely that proton-initiated cascades (with usually broad 10 SENNO, MURASE, and MÉSZÁROS PHYSICAL REVIEW D 93, 083003 (2016) Another possible subclass of interest are UL GRBs, of their high local rate relative to their high-luminosity which have a much longer duration compared to classical cousins and (ii) because their low gamma-ray flux makes GRBs (but see also Ref. [32]). Their long duration may them difficult to detect with conventional electromagnetic suggest a long-lasting fall-back accretion from an extended detectors (e.g., Swift). Recently, Murase and Ioka [19] progenitor onto a black hole. Blue supergiants (BSGs) are showed that choked jets may be more favorable as sites of possible UL GRB progenitors and are believed to be efficient neutrino production. Jets which successfully common at very high redshifts [33,34]. Alternatively, such penetrate both the progenitor star and, if applicable, a long durations may be explained by a fast-rotating pulsar, circumstellar envelope (i.e., emergent jets) typically have which could account for the connection between UL GRBs, high luminosities such that they form radiation-mediated superluminous SNe and hypernovae (e.g., Refs. [35–37]). shocks, which are unfavorable for CR acceleration and Although we do not consider potential sources of UL GRBs neutrino production. Taking into account the luminosity in this work, these low-power GRBs can also contribute to and redshift distribution of LL GRBs, we show that they neutrino emission [19]. and the choked jets may contribute to the diffuse neutrino Predictions for high-energy neutrino emission from GRB flux while remaining absent from GRB joint electromag- jets of both high and low luminosity are still uncertain netic-neutrino searches. We also explicitly show the despite recent improvements in theoretical calculations (e.g., conditions required to produce choked jets with radiation- Refs. [38–44]) (although guaranteed emission is expected in unmediated shocks. the GeV-TeV range for neutron-loaded outflows; e.g., Refs. [45–48]). Irrespective of their viability as VHE II. DYNAMICS OF RELATIVISTIC JETS neutrino factories, the mechanisms for producing and the physical processes associated with low-power GRBs are still A. Model setup for emergent jet, shock breakout, largely unknown and remain intriguing open questions. and choked jet scenarios Nearby long GRBs have been associated with broad-line GRBs are thought to result from the intense emission Type Ic SNe (e.g., GRB 980425, 060218, and 100316D), from relativistic jets that successfully penetrate a progenitor which are known to be caused by the collapse of massive star, and an understanding of jet propagation is stars that eject their outer envelopes. LL GRBs have been of undoubtedly relevant (e.g., Refs. [26,53,54]). It would be special interest since they show intermediate properties natural to expect that the radiation mechanism of LL GRB between GRBs and SNe and have been associated with gamma-ray emission is similar to that of classical GRBs transrelativistic SNe [49]. Both types of transients may be [50,55,56]. The simplest such model is a scaled-down driven by jets [31,50], and the study of LL GRBs may offer version of the classical GRB, where dissipation occurs in a clues to the GRB-SN connection [51,52]. mildly relativistic jet which has emerged outside of the In this work, based on the above motivation we consider progenitor star and any circumstellar material. We call this the VHE neutrino emission from jets choked by dense scenario the emerging jet (EJ) model (see Fig. 1, right external material, as well as any subsequent shocks result- panel). For EJs, prompt neutrino emission is produced ing from the jet acting as a relativistic piston. In particular, together with prompt gamma-ray emission outside the star, we focus on scenarios which may produce LL GRBs. identical to the scenario expected from classical GRBs Under the current constraints imposed by the IceCube [29,30,57]. analyses mentioned above,Hidden such LL GRBs Gamma are attractive as -RayAnother Burst interpretation Jets of LL GRBs which has received the originators of the diffuse VHE neutrino flux (i) because attention is the shock breakout emission model, where the Orphan Neutrinos Precursor Neutrinos Prompt Neutrinos shock breakout Emerging Jet Shock Breakout Stall Radius high-power low-powerStall Radius Choked Jet Choked Jet Extended Extended Extended Material Material Material Progenitor Progenitor Progenitor CE Core CE Core CE Core FIG. 1. Left panel: The choked jet modelKM for& Ioka jet-driven13 PRL, SNe. OrphanSenno neutrinos, KM & Meszaros are expected16 since PRD, electromagnetic Tamborra emission& Ando from 16 PRD the jet is hidden, and such objects may be observed as hypernovae. Middle panel: The shock breakout model for LL GRBs, where transrelativisticShort GRB shocks jets areembedded driven by chokedin the jets.merger A precursor ejecta neutrino signalPromising is expected since GW the gamma-ray emitters emission (~kHz) from the shock breakout occurs significantly after the jet stalls (e.g., Ref. [26]). Right panel: The emerging jet model for GRBs and LL GRBs. Both neutrinos and gamma rays are produced by theUL successful GRB jet, and bothLong messengers GRBs can be observed as prompt emission. - Can explain the 10-100 TeV n flux 083003-2 - Testable w. stacking analyses (currently limited by SN samples -> improved in the LSST era) Short GRBs (NS-NS/BH mergers) Levan+14 ApJ - Coincident w. aLIGO Kimura, KM+ 17 ApJL, 18 PRD, Carpio & KM 20 PRD <~1 event/yr with Gen-2 Neutrinos from Supermassive Black Hole Mergers Yuan, KM, Kimura & Meszaros 20 PRD Promising GW emitters (~10mHZ) - Even non-spinning black holes merge into a spinning black hole - Post-merger jets are launched - SMBH jets could significantly contribute to the 10-100 PeV neutrino flux - Coincident w. LISA events <~ 0.1-0.2 events/yr with Gen2 “High-Energy” Neutrinos from Supernovae - Enhanced circumstellar material: ubiquitous for supernova progenitors - Type II: ~100-1000 events of TeV n from the next Galactic SN ex. Betelgeuse: ~103-3x106 events, Eta Carinae: ~105-3x106 events - Large statistics: real-time monitoring of CR acceleration & new physics tests - Supernovae as “multi-messenger” & “multi-energy” neutrino source 7 IIn d=10 kpc Ln 6 II-P II-L/IIb MeV n 5 Ibc 4 ) 3 log(N 1 0 background (atm. + astro) -1 GeV-PeV n -2 -3 103 104 105 106 107 t [s] KM 18 PRDR ~10 sec ~0.1-1 day En Current and Future From Astro2020 US decadal survey (1903.04334) see also KM & Waxman 16 PRD 6 10 107 LL AGN discovery potential for discovery potential for 5 steady source candidates 10 106 transient source candidates ] starburst & GC/GG-int in 10 years ] 3 in 10 years 4 1 10 105 yr 3 SNe & newborn pulsars [Gpc 103 RQ AGN GC-acc 4 10 O [Gpc hypernovae 2 3 10 ˙ r 10 RL AGN density 10 102 LL GRB BL Lac local 1 10 blazars 0.1 IceCube 1 IceCube local rate density HL GRB effective 10 2 5 IceCube 5 IceCube ⇥ FSRQ 0.1 ⇥ jetted TDE 20 IceCube 20 IceCube 3 ⇥ 2 ⇥ 10 10 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 effective neutrino luminosity Ln[erg/s] effective bolometric neutrino energy [erg] En - Non-detection of neutrino event clustering constrains source population → Rare source classes (e.g., gamma-ray bursts) should be “subdominant” - Identifying the main sources of IceCube ns: ~0.1-0.2 deg may be necessary but might be easier below 100 TeV or above 10 PeV Summary Where do high-energy neutrinos originate from? g-ray flux ~ n flux ~ CR flux → importance of multi-messenger connections - CR reservoirs: astro-particle unification is possible Measuring the spectrum beyond a few PeV is a key - New components, including CR accelerators/cosmogenic ns, may appear The sources would be more powerful so identification may be easier Searching for the sources of medium-energy neutrinos is relevant - IceCube 10-100 TeV data imply the existence of hidden CR accelerators Connection with MeV g rays and hard X rays may be a key - Undoubtfully, searches for Galactic sources are important Transients: unique chances -> need strategic multi-messenger searches - TXS 0506+056 and other coincidences: need more data & theoretical studies - GW-n coincidences: Gen2-like sensitivities would be necessary - Supernovae: high-statistics detection is possible