Neutrino Flavor Ratios Modified by Cosmic Ray Secondary- acceleration

Transcription

1 Neutrino Flavor Ratios Modified by Cosmic Ray Secondary- acceleration ref.) NK & Ioka 2015, PRD accepted (arxiv: ) Norita Kawanaka (Univ. of Tokyo) Kunihito Ioka (KEK/Sokendai) TeV Particle Kashiwa- no- ha 26-30/10/2015

2 High Energy Neutrinos and Cosmic Rays IceCube: 54 events in 30 TeV 2 PeV TeV-PeV neutrinos = the probe of high energy CRs emitted via interactions between accelerated CR protons and (1) ambient matter or (2) photon field (1) p + p π + µ + +ν µ e + +ν µ +ν e +ν µ or π µ +ν µ e +ν µ +ν e +ν µ (2) p +γ π + µ + +ν µ e + +ν µ +ν e +ν µ roughly speaking Cosmic ray accelerator = HE neutrino factory flavor ratio at a source ν e : ν µ : ν τ = 1 : 2 : 0

3 Neutrino Flavor Ratio at the Earth intrinsic observed mixing matrix Φ νe : Φ νµ : Φ ντ =1: 2 : 0 Φ νe : Φ νµ : Φ ντ 1:1:1 à For initial flux ratio, the observed ratio is expected to be Recent results of IceCube (35 TeV 2 PeV) consistent with Φ νe : Φ νµ : Φ ντ 1:1:1 (IceCube collab. 2015) (The best fit value is 0 : 0.2 : 0.8)

4 Modification of Neutrino Flavor Ratio 1. Synchrotron/IC cooling of π/µ π/µ would lose their energy before they decay into ν i à The neutrino spectra would be softened, and the flavor ratio is also affected (Kashti & Waxman 2005, etc.) 2. Re- acceleration of π/µ ß this talk π/µ would be accelerated by shocks and/or turbulence before they decay into ν i à The neutrino spectra and flavor ratio would be modified! (Winter et al. 2014, etc.) The neutrino spectra and flavor ratio will tell us some important properties of CR accelerators (magnetic field, acceleration process, etc.)

5 Re- acceleration of Secondary CRs (π/µ) shock acceleration of primary protons à secondary π/µ production à π/µ are reaccelerated at the shock before their decay (τ π =2.6x10-8 γ π s, τ µ =2.2x10-6 γ µ s) proton π/µ shock front ν µ,e à The energy spectra of π/µ would be harder than those of their primary particles # Stochastic acceleration is also possible (Murase et al. 2012). downstream upstream

6 Re- acceleration of secondary π Convection- Diffusion equation for the distribution function f π (one- dimensional, stationary, neglecting synchrotron cooling) diffusion decay source term velocity field: source term: proportional to the distribution of primary protons p ξ π p p (ξ π 0.2) In the following discussion we assume Bohm diffusion (D(p) p)

7 Solve the Transport Equation of π upstream downstream at the shock front: A π, B π : p- independent factors ~ D(p) u 1 2 Q π,0 p ( ) = t acc

8 Re- acceleration of secondary µ Convection- Diffusion equation for the distribution function f µ diffusion decay source term source term:proportional to the distribution of primary particles, f π (shown in the last slide): ξ µ 0.75

9 Solve the Transport Equation of µ upstream & downstream at the shock front: q ± i,a, q ± i,b ~ Q µ

10 Neutrino spectra where ξ νµ 0.25, ξ νµ 0.33, ξ νe 0.33

11 Application: low- power GRBs from Murase & Ioka (2013) IceCube observations have ruled out typical long GRBs as the main source of HE neutrinos (Abbasi+12; He+ 2012) Low- power GRBs (ultra- long GRBs, LLGRBs) are still not strongly constrained. Consider the internal shocks occurring inside a star π/µ can be re- accelerated before their decay

12 Results: neutrino spectra (spectra at the source) solid:total dotted:reaccelerated dashed:other ν µ L Β = erg/s, Γ =80, Δt =1 msec, β rel =0.5, Q π (E) E -2 ν e Note: E ν > a few ev à t i,syn <~ t acc : high energy cutoff due to the cooling of π/µ would appear When τ π,µ >~ t dyn =ΓΔt, the reaccelerated component (harder) starts to dominate over the other component à appears as a flat excess at the high energy range

13 Results: flavor ratio (ν µ :ν e ) ratio at the source propagation ratio at the Earth original value Φ νµ / Φ νe = 2 ß The asymptotic ratio is determined from the ratio of t acc to τ µ f π,acc (x,p)/τ π ~ Q π (x,p)t acc /τ π f µ,acc (x,p)/τ µ ~ Q µ (x,p)t acc /τ µ ~[f π (x,p)/τ π ]t acc /τ µ ~[Q π (x,p)t acc /τ π ] (t acc /τ µ ) taking into account the flavor oscillation during propagation ~ 1.8 : 1 (in the limit t acc /τ µ 0) à One can constrain the acceleration timescale at the source!

14 Summary (for the detail, see arxiv: ) The spectra and flavor ratio of high energy neutrinos would be modified by the shock re- acceleration of secondary π/µ. The asymptotic value of the flavor ratio in the high- energy range is determined from the ratio of the acceleration timescale (t acc ) to the decay timescale of µ (τ µ ). The combination of the neutrino spectra and flavor ratio may tell us some properties of CR accelerators (especially the acceleration timescale).

15 various timescales π parameters: L Β = erg/s, Γ =80, Δt =1 msec, β rel =0.5 (rel. velocity of colliding shells) t acc : acceleration timescale t i,syn : sync. cooling timescale t i,ic : IC cooling timescale t i,dec : lifetime of a particle i t pγ : pγ interaction timescale t dyn : dynamical timescale µ t acc >> t i,syn when ε i >~ ev à cooling of π/µ should be taken into account