Recycling Galactic Cosmic-Ray Nuclei by Shear Acceleration: A Radio - - PowerPoint PPT Presentation

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Recycling Galactic Cosmic-Ray Nuclei by Shear Acceleration: A Radio - - PowerPoint PPT Presentation

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Recycling Galactic Cosmic-Ray Nuclei by Shear Acceleration: A Radio Galaxy Model for Ultrahigh-Energy Cosmic Rays Shigeo S. Kimura Center for Particle Astrophys. PSU (IGC Fellow) Dept. Astronomy & Astrophys., PSU Dept. Physics,

slide-1
SLIDE 1

Recycling Galactic Cosmic-Ray 
 Nuclei by Shear Acceleration: 
 A Radio Galaxy Model for 
 Ultrahigh-Energy Cosmic Rays

Shigeo S. Kimura

Collaborators Bing Theodore Zhang (Beijing Univ.), Kohta Murase (PSU, YITP)

Center for Particle Astrophys. PSU (IGC Fellow)

  • Dept. Astronomy & Astrophys., PSU
  • Dept. Physics, PSU

ref) SSK, T.B. Zhang, K. Murase in prep.

slide-2
SLIDE 2

Outline

  • Introduction
  • Shear Acceleration in FR-I radio galaxies
  • UHECRs as Reaccelerated Galactic Cosmic Rays
  • Summary
slide-3
SLIDE 3

Outline

  • Introduction
  • Shear Acceleration in FR-I radio galaxies
  • UHECRs as Reaccelerated Galactic Cosmic Rays
  • Summary
slide-4
SLIDE 4

Ultra-High Energy Cosmic Rays

  • Air shower experiments reveal the existence of

extremely efficient accelerators in the Universe.

  • Ecut ~ 40—50 EeV ~ GZK cutoff energy

(E/eV)

10

log

17.5 18 18.5 19 19.5 20 20.5

))

2

eV

  • 1

sr

  • 1

s

  • 2

J /(m

3

( E

10

log

22.5 23 23.5 24 24.5

E[eV]

18

10

19

10

20

10

22217 13210 7774 4611 2639 3450 2629 2006 1344 60423 34861 26325 16317 10991 7585 5221 3491 2238 1405 888 569 267 130 54 10 4 1

Auger (ICRC 2015 preliminary)

(E/eV)

10

log 17 17.5 18 18.5 19 19.5 20 20.5 ]

  • 1

sr

  • 1

s

  • 2

m

2

[ eV

24

/10

3

E × J(E)

  • 1

10 1 10 AGASA Auger HiRes-I HiRes-II TA SD

Abu-zayyat+13 Auger (ICRC 15)

slide-5
SLIDE 5

Luminosity density

  • UHECR flux: ~ 0.1 particle km-2 yr-1 @100 EeV
  • Mean-free path of UHECRs: 100 Mpc
  • Luminosity density: 3x1043 erg Mpc-3 yr -1

10

19

10

20

10

2

10

3

(α−1)teff*c (Mpc) E(eV)

m=0 α=2 m=0 α=2.7 m=0 α=3 m=3 α=2 m=3 α=2.7 m=3 α=3 (τ−1

0,epexp(−Ec,ep/E)+τ0,π −1 exp(−Ec,π/E)+2H0)−1

(E/eV)

10

log

17.5 18 18.5 19 19.5 20 20.5

))

2

eV

  • 1

sr

  • 1

s

  • 2

J /(m

3

( E

10

log

22.5 23 23.5 24 24.5

E[eV]

18

10

19

10

20

10

22217 13210 7774 4611 2639 3450 2629 2006 1344 60423 34861 26325 16317 10991 7585 5221 3491 2238 1405 888 569 267 130 54 10 4 1

Auger (ICRC 2015 preliminary)

waxman 11

slide-6
SLIDE 6

Source Candidates

  • AGN jets





  • GRBs





  • Pulsars

B (G) R (cm)

1015 1015 1020 1025 1 AU 1 pc 1 kpc 1 Mpc 1010 1010 105 105 100 10–5 10–10 Neutron star P r

  • t
  • n

Emax ≤ 1 021 e V G R B A G N j e t s F e Emax ≤ 1 020 e V White dwarf AGN SNR Hot spots IGM shocks

Hillas 84 Kotera+11 Takahara 90
 Murase+12
 Araudo+16 Waxman 95
 Globus+15
 Asano+16 Blasi + 00, Fang+12

slide-7
SLIDE 7

Composition

  • Proton @ E~ EeV,
  • gradually becomes heavier for higher energy
  • Data is consistent for two experiments, 


but interpretation can be changed by analysis

Energy log10(E/eV)

<Xmax > [gm/cm2] Proton Iron

18.5 19 19.5 20 650 700 750 800 850 Data QGSJETII−03 QGSJET−01c SYBILL 2.1

Auger ICRC 15 TA 15

slide-8
SLIDE 8

Fitting requirement

  • Emax,p ~ 6 EeV
  • Hard source spectrum: s ≲ 1
  • Abundance for Auger data: 


much heavier than the Galactic composition ratio

  • Need another EeV component

0.01 0.1 1 10 100 1000 17.5 18 18.5 19 19.5 20 20.5

E2 dN/dE [eV cm-2 s-1 sr-1] log10 Energy [eV]

EFe, max=1020.2 eV α=0.6 A=1-2 A=3-6 A=7-19 A=20-39 A=40-56 650 700 750 800 850 17.5 18 18.5 19 19.5 20 20.5

<Xmax> [g cm-2] log10 Energy [eV]

protons Iron Auger 2014

Aloisio+14, Taylor+15

slide-9
SLIDE 9

Espresso Acceleration

  • Re-acceleration of galactic CRs by AGN jets


—> composition & spectrum is well fitted

  • However, this model require extremely strong jets


—> No source inside the UHECR horizon

b ( ) m m

  • m º

4 ( ) b bm ¢ = G

  • = G
  • ¢

¢ = ¢ m¢ º ¢ ¢ bm bm m m b bm = G

  • +

¢ = ¢ + + ¢ m m ¹ g G

  • m

b ¢ = - z ¢ = - ¢ b b G

  • W¢ ¢ + G

W¢ ¢

  • j

p ¢ º W¢ ¢ j p ¢ = j p p ¢ Î g » ´ ¢

m

  • j¢

á ñ = G

j¢

r µ µ » r r µ µ

  • J

D »

  • ~

m

  • J

» D p F

  • p

J F D

  • J

D

  • f

=

  • ´
  • »

¹

< f f µ ¶ µ

g =

  • >

µ

g d

  • +

E2.7 Flux(E) [m-2 s-1 sr-1 GeV1.7] ln (A)

Caprioli 15

slide-10
SLIDE 10

Anisotropy

  • weakly clustering, but not statistically significant
  • the result of cross correlation analysis is consistent

with isotropic arrival —> Nsource ≳ 10-6 Mpc -3

  • Luminous sources are disfavored

Auger: Galactic coordinate

  • +
  • +

= ´

  • a d =
  • = -

) = 3 = ´

  • a d =

> y y = y = =

  • 4

TA: equatorial coordinate

Takami+ 12

(d)

Auger 15 Fang+16 Auger 15 TA 14

slide-11
SLIDE 11

Purpose

  • Re-cycling galactic CRs works for the composition


—> consider AGN Jets

  • Harder spectrum is required


—> Shear acceleration

  • High source density is favorable from anisotropy constraints


—> FR-I galaxies

Consider recycling galactic cosmic rays by shear acceleration in the FR-I radio galaxies

slide-12
SLIDE 12

Outline

  • Introduction
  • Shear Acceleration in FR-I radio galaxies
  • UHECRs as Reaccelerated Galactic Cosmic Rays
  • Summary
slide-13
SLIDE 13

Shear Acceleration

  • region 1 & 3: 


tail-on collision
 —> E ⤵

  • region 2 & 4:


head-on collision
 —> E ⤴

For continuous shear layer, distribution function diffuses in p space = = ( ) ( ) ¶ ¶ = ¶ ¶ ¶ ¶

  • +

⎛ ⎝ ⎜ ⎞ ⎠ ⎟ f p t p p p D f p p 1

p 2 2

= + ) d d =

  • g

= = d d = á ñ d d = +

  • =

d d á ñ d d á ñ d d á ñ µ á ñ

ò ò

p p á ñ = á ñ = ¶ ¶ = ¶ ¶ ¶ ¶

ò

p á ñ = ¶ ¶ = p = x =

ò x x x

= á ñ +

  • =

= = = = = =

d d á ñ

Earl 88, Subramanian 99, Rieger+ 06

slide-14
SLIDE 14

Shear Acceleration

  • gyro radius > size of shear layer → discrete shear
  • Discrete shear: no analytic formulation


From MC simu., dN/dE ~ E0

slide-15
SLIDE 15

Rjet Resc Jet Cocoon Bjet Bext

Model Setup

  • Consider kpc away from the core
  • Jet becomes cylindrical around kpc scale
  • Mildly relativistic jet βj ~ 0.6
  • Jet is long, Ljet ~ 20 kpc >> Rjet ~ 300 pc

Kchekhovskoy+16

slide-16
SLIDE 16

Rjet Resc Jet Cocoon Bjet Bext

Model Setup

  • We perform Monte Carlo simulation
  • Bohm diffusion, λ ~ rgc/3
  • isotropic scattering at the fluid rest frame
  • Resc ~ 10 Rjet

Kchekhovskoy+16

slide-17
SLIDE 17

Simulation results

  • Hard spectrum owing to shear acceleration
  • dN/dE ~ E0 for E<Epeak 


Consistent with previous works

ELE [s-1] E[eV]

slide-18
SLIDE 18

Analytic Estimate

  • n ⟨∆t⟩p ∼ 2Rcoc/(c),

e energy gain per cycl as ⟨∆E/E⟩p ≃ 4Γ2

jβ2 j /3

, we can write t ≃ 3

e tacc ≃ 3Rcoc/(2β2

j c).

ssion only for a transr

e tacc = ⟨∆t⟩p/⟨∆E/E⟩p, w

from simulation results

  • Acceleration Time:
  • Escape time:

, tesc ∼ R2

coc/(6DBohm).

Epeak ≃ eZs 3 Γ2

jβ2 j BcocRcoc ∼ 2.1ZsB4R3β2 6 EeV,

tting tacc ≃ tesc, w

Consistent with the MC simulations Achieve a few EeV for protons

slide-19
SLIDE 19

Outline

  • Introduction
  • Shear Acceleration in FR-I radio galaxies
  • UHECRs as Reaccelerated Galactic Cosmic Rays
  • Summary
slide-20
SLIDE 20

Re-acceleration of 
 galactic cosmic rays

  • Galactic cosmic rays (GCRs) are diffusing in halo
  • Jet penetrates halo: 


Low-E GCRs (< Einj) are advected & cools down,
 High-E GCRs (> Einj) are injected to the shear accel. Halo

cocoon jet

Low-E CR High-E CR

slide-21
SLIDE 21

Re-acceleration of 
 galactic cosmic rays

  • We can obtain hard spectrum & heavier composition
  • (fH, fHe, fC-O, fNe-Al, fSi-K, fCa-Mn, fFe) =(72, 21, 4.3, 1.1, 0.54, 0.14, 0.38 )
  • Luminosity ~ 1041 erg/s, number density ~ 10-5 Mpc-3


—> consistent with the expected luminosity density & anisotropy

E2LE [erg s-1] E[eV]

  • Since FR-I radio galaxies are

elliptical, we enhance metal abundance for injected CRs.

  • p, He : the Galactic CR

  • thers : the Galactic CR x3

SSK+ in prep

slide-22
SLIDE 22

Propagation of IGM

  • Using CRpropa code that includes


a) decay of nuclei
 b) photomeson production: p+γ —> p + π
 c) photodisintegration : NA+γ —> NA-1 + p
 d) photo-pair production: p+γ —> p + e+ + e-
 (the code includes other channels)

  • Radiation fields: 


EBL (infrared), CMB (radio)

  • G. Müller+ ICRC 13

EeV Nucleus Neutrino, Photon

Batista + 16

slide-23
SLIDE 23

Spectrum at the Earth

  • Compatible with the

Auger result.

  • A bit lower flux

around E ~ 30 EeV

  • We need another

EeV component

SSK+ in prep

cf.) Aloisio+14

slide-24
SLIDE 24

Composition at the Earth

  • Consistent with the

Auger feature: 
 heavier for higher E

  • < ln A> is heavier 


for E > 10 EeV

  • σ2(ln A) is comparable
  • For higher Epeak model, 


<ln A> is better, but the spectrum is worse

SSK+ in prep

slide-25
SLIDE 25

Outline

  • Introduction
  • Shear Acceleration in FR-I radio galaxies
  • UHECRs as Reaccelerated Galactic Cosmic Rays
  • Summary
slide-26
SLIDE 26

Summary

  • Experiments for UHECRs show


a) Cutoff energy: 40-50 EeV
 b) Luminosity density: 3x1043 erg Mpc-3 yr -1 
 c) Heavier composition for higher energy
 d) Large number density: n >10-6 Mpc-3

  • The model of re-acceleration of galactic CRs by

shear in FR-I radio galaxies are consistent with all the requirement above.

E2LE [erg s-1]

E[eV]