Origin of cosmic rays Vladimir Ptuskin IZMIRAN Russia/University of Maryland USA FFP14, Marseille
Outline Introduction Voyager 1 at the edge of interstellar space Cosmic ray transport in the Galaxy Supernova remnants main Galactic accelerators Positrons in cosmic rays Structure of the knee Energy limit for galactic sources Extragalactic cosmic rays: transport and sources High energy neutrinos of cosmic origin
CR spectrum at Earth GRB AGN interacting galaxies ultrafast pulsar E -2.7 cosmic ray halo, Galactic wind cosmological shocks Fermi bubble JxE 2 10 9 ev 10 20 ev LHC extragalactic 1/km 2 /century Sun pulsar, PWN SNR WMAP haze GC stellar wind close binary Galactic disk N cr = 10-10 cm -3 - total number density in the Galaxy w cr = 1.5 ev/cm 3 - energy density E max = 3x10 20 ev - max. detected energy Q cr = 10 41 erg/s power of Galactic CR sources A 1 ~ 10-3 dipole anisotropy at 1 100 TeV r g ~ 1 E/(Z 3 10 15 ev) pc - Larmor radius at B=3x10-6 G
Voyager 1 at the edge of interstellar space launched in 1977, 70 kb, 22 w 10 3 direct measurements of interstellar CR spectra at low energies 10 2 after E. Stone 2013 particle /(m 2 sec sr MeV/nuc) 10 1 10 0 10-1 10-2 10-3 10-4 He low energies: Voyager 1 Stone et al. 2013 high energies: BESS Pamela Sparvoli et al 2012 H 10-5 10 0 10 1 10 2 10 3 10 4 10 5 energy, MeV/nuc
Golden age of new CR measurements Spacecrafts: Voyagers; ACE, Pamela, Fermi/LAT, AMS Balloons: BESS, CREAM, TRACER Cherenkov telescopes: HESS, MAGIC, VERITAS EAS detectors: KASCADE-Grande, MILAGRO, ARGO-YBJ, TUNKA, EAS-TOP, IceCube/IceTop, Auger, Telescope Array
M51 traversed matter thickness X ~ 12 g/cm 2 at 1 GeV/nuc (surface gas density of galactic disk ~ 2.5 10-3 g/cm 2 ) energy balance: ~ 15% of SN kinetic energy go to cosmic rays to maintain observed cosmic ray density Ginzburg & Syrovatskii 1964 steady state: (without energy losses and nuclear fragmentation) J cr (E)= Q cr (E) T(E) source term, SNR two power laws! E -2.1 x E -0.6 escape time from the Galaxy, 10 8 yr at 1 GeV, resonant scattering in random magnetic field 1/k res = r g
galactic wind driven by cosmic rays Ipavich 1975, Breitschwerdt et al. 1991, 1993 u inf = 500km/s R sh = 300 kpc CR scale height is larger then the scale height of thermal gas. CR pressure gradient drives the wind. + cosmic ray streaming instability with nonlinear saturation Zirakashvili et al. 1996, 2002, 2005, VP et al. 1997, 2000, D 1 1.1 s vb p p q cr Zmpc Zmpc 27 2 ~ 10 cm / s, (3 1) / 2 2.7, at 2.1 s s X s 1 2 H ef p p ~ ~ ~ D Zmpc Z 0.55
why power law? Fermi 1949, 1954 p u 2 u u p p, or - 1st or 2nd order acceleration v v 2 approximate for ( ) ( ) : Fermi formula γ =1+ τ τ a l J E p f p p -1 ; spectrum at / 1: p. a l Krymsky 1977, Bell 1978, u 2 shock u 1 diffusion diffusive shock acceleration...... a 3, u u u l 1 2 2 3 γ =1+ =2 r-1 1 at compression ratio 4 u2 r u
u sh 10 51 erg SNR shock ushr sh >10 D(p) D(р) should be anomalously small both upstream and downstream; CR streaming creates turbulence in shock precursor Bell 1978; Lagage & Cesarsky 1983 ush Emax 0.3 Ze B R c E max,ism =10 13 10 14 Z ev for B ism = 5 10-6 G Bohm limit D B =vr g /3: - condition of acceleration and confinement sh streaming instability gives B >> B ism in young SNR Bell & Lucek 2000, Bell 2004, Pelletier et al 2006; Amato & Blasi 2006; Zirakashvili & VP 2008; Vladimirov et al 2009; Gargate & Spitkovsky 2011 confirmed by X-ray observations SN 1006, Cas A, RCW 86, RX J1713.7-3946 under extreme conditions (e.g. SN1998 bw): E max ~ 10 17 ZeV, B max ~ 10-3 G
numerical simulations of particle acceleration and radiation in SNR Berezhko et al. 1994-2006, Kang & Jones 2006 Zirakashvili & VP 2012, semianalytic models Blasi et al.(2005), Ellison et al. (2010) ) Zirakashvili & VP 2012 Zirakashvili et al 2014 Cas A radio polarization in red (VLA), X-rays in green (CHANDRA), optical in blue (HST)
calculated spectrum of Galactic cosmic rays: VP, Zirakashvili, Seo 2010 JxE 2.75 solar modulation source spectra produced by SNRs protons data from HEAO 3, AMS, BESS TeV, ATIC 2, TRACER experiments 4 sn4 cp ( p)/ sn hydrodynamic eqs.+ P cr ; diffusion-convection transport eq. for CR with Alfvenic drift interstellar spectrum of all particles extragalactic component «knee» is formed at the beginning of Sedov stage 15 1/6-2/3 Eknee Z =1.1 10 Wsn,51n M ej ev data from ATIC 1/2, Sokol, JACEE, Tibet, HEGRA, Tunka, KASCADE, HiRes and Auger experiments
positrons in cosmic rays; pulsars, dark matter,... collection of data Mitchell 2013 Harding & Ramaty 1987 Ting presentation 2013
knee and beyond p,he knee 2nd knee Berezhnev et al. 2012 structure above the knee different types of nuclei, E knee ~ Z different types of SN transition to extragalactic component JxE 3 p He Fe JxE 2.7 Kampert 2013
summary by Tsunesada 2013 knee JxE 2.75 GZK suppression? E EeV r g =1 Z B μg Kpc <lna> EPOS 1.99 Kampert & Unger 2012
energy loss of ultra-high energy cosmic rays pair production p pe + e - pion production microwave & EBL photons γ γ p N π E GZK expansion GZK cutoff at E GZK ~ 6 10 19 ev Greisen 1966; Zatsepin & Kuzmin 1966 energy loss length z = 0 photodisintegration of nuclei Stecker 1969 Universe expansion - (1/E) (de/dt) adiabatic = H H 0 =100h km/(s Mpc), h=0.71
extragalactic sources of cosmic rays energy release in units 10 40 erg/(s Mpc 3 ) needed in CR SN AGN jets GRB newly born accretion on at Е > 10 19.5 ev fast pulsars galaxy clusters (< 5ms) 3 10-4 (Auger) 3 10-1 3 3 10-4 10-3 10 kin. & 6 10-2 for X/gamma rotation strong shocks 8 10-3 for E>10 9 ev L kin > 10 44 erg/s 20 1/ 2 45 AGN jets max jet fast new born pulsars B = 10 12 10 13 G E 10 Z β L /10 erg/s ev Lovelace 1976, Biermann & Strittmatter 1987, Norman et al 1995, Lemoine & Waxman 2009 19 4 E 10 Z Ω / 10 sec ev max Gunn & Ostriker 1969, Berezinsky et al. 1990, Arons 2003, Blasi et al 2000, Fang et al. 2013 2 1/2
Auger transition to heavy elements above 10 19 ev -anisotropy TA+HiRes proton dominated composition - no significant anisotropy (?) for heavy composition: E max /Z = 4 x10 18 ev easier to accelerate cosmic rays but difficult to identify their sources; production of neutrinos is suppressed (Berezinsky - disappointing model)
very high energy neutrinos of cosmic origin IceCube neutrino detector Aartsen et al. 2014 Aartsen et al. 2014 E dn/ de ν 3-year data: excess of 37 neutrinos above atmospheric background (>5.7 sigma) at 3.10 13 to 2.10 15 ev 100 TeV 1000 TeV (0.95±0.3) 10 GeV cm s sr 2-8 -2-1 -1 ν - cosmic neutrino flux per flavor with possible suppression above 2 PeV; - equal flavor ratio 1:1:1; - isotropic sky distribution
neutrino production in cosmos is possible via interactions pγ, pp(n) and decay chains + + + + π μ ν, μ e ν ν μ e μ plus neutrino oscillations _ 28 Razzaque 2013 - Galactic sources may account only for a minority of events - cosmogenic (GZK) neutrino production is inefficient - can be produced in extragalactic sources of UHE cosmic rays; not in GRB WB bound? Waxman & Bahcall 1999
some coming projects JEM-EUSO (2016, Extreme Universe Observatory, > 3 10 19 ev, 100000 km 2 from space, instantaneous aperture ~100 PAO ) sensitivity LHAASO (2013-2018, Large High Altitude Air Shower Observatory, Tibet 4300 m, gamma-rays and CRs till the knee and 1 EeV, 1 km 2 array of electron and muon detectors for gamma rays > 30 TeV, 90000 m 2 water Cherenkov detector array for gamma rays >100 GeV, 24 wide field Cherenkov telescopes and 5000 m 2 shower core detectors for CRs > 30 TeV) CTA (2018, Cherenkov Telescope Array, 100 GeV 100 TeV, 100 telescopes ( 5m to 23 m diameter); two arrays to cover full sky; 10 times better sensitivity makes about 200 SNRs visible) Tunka-HiSCORE (wide-angle Cherenkov gamma observatory, 1-100 km 2, search for PeVatrons, E cr =10 14 10 18 ev) CALET (2014, scintillation calorimeter on ISS, e+ e- up to 20 TeV) ISS-CREAM (2015, on ISS by Space-X)
Conclusions Cosmic ray origin scenario where supernova remnants serve as principle accelerators of cosmic rays in the Galaxy is strongly confirmed by recent numerical simulations. Accurate data on cosmic rays in the energy range 10 17 to 10 19 ev, where the transition from Galactic to extragalactic component occurs are becoming available. Eliminating the uncertainties with energy spectrum and composition is necessary for understanding of cosmic ray origin at the highest energies.