Exploring Powerful Extragalactic Particle Accelerators with X-rays, - - PowerPoint PPT Presentation

Exploring Powerful Extragalactic Particle Accelerators with X-rays, Gamma-rays and Neutrinos

Felix Aharonian DIAS/Dublin & MPIK/Heidelberg

TeV PA 2010, Paris, July 19-23

Gaisser&Stanev 2009

2009

Cosmic Rays

HiRes/AUGER confirm the existence of a spectral break/cutoff around 1020 eV! is this the so-called GZK cutoff expected for the sources located beyond 100 Mpc? not necessarily - there is another fundamental reason to expect a cutoff around 1020eV because of limited efficiency for particle acceleration in available astronomical objects

below knee around 1015 eV

three components of Cosmic Rays Galactic

above ankle around 1018 eV between knee and ankle

ExtraGalactic ???

suspected sites of acceleration of 1020 eV CRs based on the condition: size > Larmor radius:

“Hillas Plot”

PM Bauleo & JR Martino Nature 458, 847-851 (2009)

Text

(R/1pc)x(B/1G) > 0.1(E/1020 eV)

size > Larmor radius: (R/1pc)x(B/1G) > 0.1(E/1020 eV) a necessary but not sufficient condition: it implies (1) minimum acceleration time tacc=RL/c=E/eBc and (2) no energy losses ★ the acceleration in fact is slower: tacc=(1-10)η RL/c (c/v)2 with η>1 and shock/bulk-motion speed v<c (η=1 - Bohm diffusion) for this reason galaxy clusters cannot accelerate particles beyond 1019 eV ★ energy losses due to the proton synchrotron or curvature radiation in compact objects become severe limiting factor

even so, the AGN jets and GRBs are the most likely sources responsible for acceleration of 1020 eV protons and nuclei

Particle acceleration in Galaxy Clusters

all ingredients for effective acceleration of cosmic rays

✓ formation of strong accretion shocks ✓ magnetic field of order 0.1-1 μG ✓ shock velocity - few 1000 km/s ✓ acceleration time ∼ Hubble time

but protons cannot be accelerated to 1020 eV

pair production losses shape the proton spectrum around the cut-off:

• small bump,
• non-exponential cut-off

Proton Spectrum

Vannoni,FA, Gabici 2009

c

• n

f i n e m e n t energy losses c

• n

f i n e m e n t energy losses

acceleration sites of 1020 eV CRs signatures of extreme accelerators?

✓ synchrotron self-regulated cutoff:

✓ neutrinos (through “converter” mechanism) production of neutrons (through p interactions) which travel without losses and at large distan- ces convert again to protons => 2 energy gain ! Derishev, FA et al. 2003, Phys Rev D 68 043003 ✓ observable off-axis radiation radiation pattern can be much broader than 1/ Derishev, FA et al. 2007, ApJ, 655, 980

Aharonian et al. et al. 2002, Phys Rev D 66 023005 “hadronic” “electronic”

c

• n

f i n e m e n t energy losses c

• n

f i n e m e n t energy losses

acceleration sites of 1020 eV CRs signatures of extreme accelerators?

✓ synchrotron self-regulated cutoff:

✓ neutrinos (through “converter” mechanism) production of neutrons (through p interactions) which travel without losses and at large distan- ces convert again to protons => 2 energy gain ! Derishev, FA et al. 2003, Phys Rev D 68 043003 ✓ observable off-axis radiation radiation pattern can be much broader than 1/ Derishev, FA et al. 2007, ApJ, 655, 980

Aharonian et al. et al. 2002, Phys Rev D 66 023005 “hadronic” “electronic”

compact/magnetized objects!

acceleration and radiation of UHE protons in kpc-scale structures of AGN jets

3C 273

(R/1kpc)x(B/100μG) > 1(E/1020 eV) : protons can be acceleared to 1020 eV e.g. by relativistic shocks

FA 2002

Text Text

acceleration/radiation

• f > 1019eV protons in

sub-parsec AGN jets

proton-synchrotron

Ecut=90 (B/100G)(Ep/1019 eV)2 GeV tsynch=4.5x104(B/100G) -2 (E/1019 eV)-1 s tacc=1.1x104 (E/1019) (B/100G) -1 s

synchrotron radiation of protons:

a viable radiation mechanism Emax =300 η-1 δ GeV requires extreme accelerators: η ~ 1

FA2000

✓ because of interstellar and intergalactic magnetic fields, the information about

the original directions of cosmic rays pointing to their production sites is lost

✓ the flux of cosmic rays is contributed, most likely, by a large number of galactic

and extragalactic sources; these objects represent different source populations characterized by essentially different physical parameters – age, distance, energy budget, etc., as well as by different particle acceleration scenarios => extremely difficult the identification of sources of the isotropic flux of cosmic rays based on two measurables - the chemical composition and energy spectra

• f particles - characterizing the ”soup” cooked over cosmological timescales

but .... at extremely high energies, E ∼ 1020 eV , the impact of galactic and extragalactic magnetic fields on the propagation of cosmic rays becomes less dramatic, which might result in large and small scale anisotropies of CR flux depending on the strength and structure of the (highly unknown) intergalactic magnetic field, the highest energy domain of CRs may offer us a new astronomical discipline - ”cosmic ray astronomy”, provided that BIGM <10-9 G

proton astronomy?

extension of studies to energies 1020eV and beyond enhances chances

• f localization of particle accelerators for three independent reasons:
• with an increase of energy, the probability that a proton of 1020eV would

penetrate through IGM without significant deflections in chaotic magnetic fields increases; for IGMF << 10−9G, the deflection angle can be quite small also for lower energies, but 1020 eV is a special energy because

• deflection of protons with energy less than 1020 eV in galactic magnetic

fields exceeds 1 degree (angular resolution of UHE cosmic ray detectors)

• particles of such high energies can arrive only from relatively nearby

accelerators located within 100 Mpc. this dramatically (by orders of magnitude) decreases the number of relevant sources of ≥ 1020eV protons contributing to the observed cosmic ray flux, and correspondingly reduces the level of the diffuse background, i.e. the (quasi) isotropic flux due to superposition of contributions by unresolved discrete sources.

1020 eV - a special energy

to appear in Phys Rev D, 2010 Aug 10 issue

101 102 103 104 1018 1019 1020 1021 1022 cE/|dE/dt|, Mpc E, eV

mean free path of protons in IGM due to interactions with CMBR at z<<1

10-2 10-1 100 101 100 101 102 〈 θ2 〉1/2, deg r, Mpc

1.004⋅1019 1.019⋅1019 1.077⋅1019 3.01⋅1019 3.06⋅1019 3.26⋅1019 1.03⋅1020 1.19⋅1020 1.68⋅1021 3.75⋅1020 1.32⋅1021 2.02⋅1023 1.42⋅1021 5.61⋅1021 8.26⋅1023 Ef=1⋅1019 eV Ef=3⋅1019 eV Ef=1⋅1020 eV Ef=3⋅1020 eV Ef=1⋅1021 eV

mean deflection angle of protons for fixed final (observed) energy Ef for IGM B=1 nG; λ=1Mpc. Numbers at curves are energies of protons at distance r from the observer

101 102 103 104 1018 1019 1020 1021 1022 cE/|dE/dt|, Mpc E, eV

mean free path of protons in IGM due to interactions with CMBR at z<<1

10-2 10-1 100 101 100 101 102 〈 θ2 〉1/2, deg r, Mpc

1.004⋅1019 1.019⋅1019 1.077⋅1019 3.01⋅1019 3.06⋅1019 3.26⋅1019 1.03⋅1020 1.19⋅1020 1.68⋅1021 3.75⋅1020 1.32⋅1021 2.02⋅1023 1.42⋅1021 5.61⋅1021 8.26⋅1023 Ef=1⋅1019 eV Ef=3⋅1019 eV Ef=1⋅1020 eV Ef=3⋅1020 eV Ef=1⋅1021 eV

mean deflection angle of protons for fixed final (observed) energy Ef for IGM B=1 nG; λ=1Mpc. Numbers at curves are energies of protons at distance r from the observer detection

• f 1021eV protons

very important!

energy spectra of protons within different solid angles

dN/dE=AE-α exp(-E/Eo);α=2, Eo=3x1020eV; Lp=1044 erg/s; B=1nG; λ=1Mpc

10-14 10-13 10-12 1019 1020 E2 F(E), erg cm-2 s-1 E, eV

r=100 Mpc 1° 2.5° 6° 15° loss-free total

10-14 10-13 10-12 1×1019 2×1019 4×1019 6×1019 E2 F(E), erg cm-2 s-1 E, eV

r=300 Mpc 1° 2.5° 6° 15° loss-free total

“bump” (just before the cutoff) - due to interactions with CMBR “sharp maximum” - due to the magnetic “filter”

for B between 10-9 to 10-7 G electrons are produced within 10 Mpc and radiate predominantly through synchrotron radiation before any significant deflection => point-like GeV /TeV gamma-rays and EeV neutrinos (FA 2002; Gabici&FA 2005)

distributions of secondary photons, electrons, neutrinos from photomeson interactions

second generation of electrons from (B-H) pair production of γ-rays more important than the contribution from the first generation of electrons

Kelner&FA 2008

secondary electrons TB-H pairst T

“photomeson electrons”t

energy spectra of synchrotron radiation of secondary (pion-decay) electrons within different angles

10-15 10-14 10-13 109 1010 1011 1012 1013 E2 F(E), erg cm-2 s-1 E, eV

r=100 Mpc B=1 nG 1 2 3 4 5 1 — 0.05° 2 — 0.16° 3 — 0.5° 4 — 1.6° 5 — 5° E0=1⋅1021 eV E0=3⋅1020 eV E0=1⋅1020 eV

10-16 10-15 10-14 109 1010 1011 1012 1013 E2 F(E), erg cm-2 s-1 E, eV

r=300 Mpc B=1 nG 1 2 3 4 5 1 — 0.05° 2 — 0.16° 3 — 0.5° 4 — 1.6° 5 — 5° E0=1⋅1021 eV E0=3⋅1020 eV E0=1⋅1020 eV

dN/dE=AE-α exp(-E/Eo) with α=2, Lp=1044 erg/s; B=1nG; λ=1Mpc

energy spectra of synchrotron radiation of secondary (pion-decay) electrons within different angles

10-15 10-14 10-13 109 1010 1011 1012 1013 1014 E2 F(E), erg cm-2 s-1 E, eV

r=100 Mpc E0=3⋅1020 eV 1 2 3 4 5 6 1 — 0.05° 2 — 0.16° 3 — 0.5° 4 — 1.6° 5 — 5° 6 — 15.8° B=100 nG B=10 nG B=1 nG

dN/dE=AE-α exp(-E/Eo) with α=2, Eo=3x1020 eV; Lp=1044 erg/s

neutrinos

10-14 10-13 1018 1019 1020 E2 F(E), erg cm-2 s-1 E, eV

r=100 Mpc B=1 nG

1 2 3 4 5

1 — 0.05° 2 — 0.16° 3 — 0.5° 4 — 1.6° 5 — 5° νµ+ν −

µ

νe+ν −

e

dN/dE=AE-α exp(-E/Eo) with α=2, Lp=1044 erg/s; B=1nG

10-14 10-13 1018 1019 1020 E2 F(E), erg cm-2 s-1 E, eV

r=100 Mpc B=1 nG

1 2 3

1 — 0.3° 2 — 0.95° 3 — 3° E0=1⋅1020 eV E0=3⋅1020 eV E0=1⋅1021 eV

Eo=3x1020eV

νμ

10-15 10-14 10-13 10-12 10-11 109 1010 1011 1012 1013 1018 1019 1020 E2 F(E), erg cm-2 s-1 E, eV

γ νµ+ν −

µ

p

10-15 10-14 10-13 10-12 10-11 109 1010 1011 1012 1013 1018 1019 1020 E2 F(E), erg cm-2 s-1 E, eV

γ νµ+ν −

µ

p

p p ν ν γ γ p γ ν

30pc 300pc ϑ=3o

ϑ=3o ϑ=0.3o

30Mpc

ϑ=0.3o ϑ=3o

Eγ Ep,ν Eγ Ep,ν spectral energy distribution of gamma rays, muon neutrinos and protons* dN/dE=AE-α exp(-E/Eo) with α=2, Eo=3x1020 eV; Lp=1044 erg/s; B=1nG

✓ if protons escape the source within a small angle towards the

• bserver δΩ, all fluxes are increased by a factor of 4π/δΩ

✓ if CR sources are located well beyond 100 Mpc - no chances to detect protons

but synchrotron GeV-TeV γ-rays and EeV neutrinos can be yet observed

arrival time distribution of protons

• A. detection of protons with arbitrary

arrival angles;

• B. protons arriving along the radius-

vector at the regitration point lg y = lg τ − 2 lg r − lg λ − 2 lgB + 2 lgE + const

E=1020 eV; Lp=1044 erg/s; B=1nG, d=10 Mpc