Astrophysical Sources of UHECRs

18 May, 2006 KAW4, Daejeon 1

Astrophysical Sources of UHECRs

Tom Jones

University of Minnesota


Outline

•Observational constraints

•Basic physical limitations on sources

•Some astrophysical models


All particle cosmic ray spectrum

UHECR

Nagano & Watson 00 LHC ppCM ZeV


Spectrum below ~100EeV pretty well known


Abbasi etal, ApJ 2005

Best Fit:80% p; QGSJet60% p; SIBYLL

UHECRComposition:could be almost all p


eV

TeV

eV

xmmmE pep

18142210

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105~

4

2

eV

T

xeV

eV

xmmmE pp

201622102

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107~

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cudtdEE

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Propagation Issue 1:Protons > 0.1 ZeV severely limited by energy losseson CMB photons (Greisen-Zatsepin-Kuzmin; GZK)1,2

Photo-pairproduction

Photo-pionproduction

Path limit: is cross section is fractional energy loss

1 Assuming ‘standard physics’2 Also an accelerator issue using local photon field


Resulting Propagation Limits Against CMB

Conditionsmatched tolook back time,adiabatic lossesincluded

ConcordanceCDM

Pair losses

Pion losses

‘GZK sphere’


Abu-Zayyad etal, APh, 18, 237 (2002)

1 EeV 1 ZeV

Number of events:

EEeV > 10: ~ 103

EEeV > 40: ~ 100EEeV > 100: ~ 10

Do we see theGZK feature?HiRes vs AGASA


Small statistics: photo-pion losses are discrete:GZK feature not yet confirmable

De Marco, Blasi & Olinto (APh, 20, 53 (2003))


Propagation issue 2:What do arrival directions tell us About the sources?

>Nearly isotropic with perhaps some clustering and/or correlations with ‘interesting’ astrophysical objects


Auger: Sky Map of Data set

Auger latitude= -36. Always sees South with limited coverage in North. Mantsch etal


AGASA Small Scale Clustering for E >4x1019eV

• Isotropic in large scale Extra-Galactic• But, Clusters in small scale (Δθ<2.5deg)

– 1triplet and 6 doublets (2.0 doublets are expected from random)– One doublet triplet(>3.9x1019eV) and a new doublet(<2.6deg)


Gorbunov etal 2004

BL Lac /UHECR Cross-correlations?

logE>19.5


Deflection of Protons >41019eV(< 100 Mpc)

Dolag etal 2003

0o360o


Astrophysical Source Energetics:Local energy density in 100 EeV CRsu~4J/c~3x10-22 J/m3~3x10-21 erg/cm3

loss~3x108yr, so

~u/loss~10-37 W/m3

~3x1044 erg/Mpc3/yr

Roughly equivalent to ~ 1 ‘AGN’ inside 100 Mpc (~2x10-7 Mpc-3)Or

Cosmic GRB rate ignoring evolution

Perhaps event cluster statistics gives a space density[Blasi & De Marco 2004] ~ 10-5 Mpc-3 from AGASA data


Some Astrophysical Accelerator Issues

• How particles of such extreme energy (~1021 eV = 1 ZeV) can be accelerated and escape; i.e, what can make a “Zevatron”?

• How to match the GZK feature (flight < 108yr above ~100 EeV) if it exists or not (source spectrum)

• How to account for an essentially isotropic distribution of detections (sources & propagation), maybe with some correlations and clustering


Emax: Some Standard Estimates for an Accelerator

•Containment: rg = (E)/(ZeB) < RE < ZeBR

•Unipolar inductor: E<ZeBR (R/c)~a ZeBR

•Diffusive shock acceleration (DSA) (nonrelativistic):acc ~ 10 /(u2

s) < R/us with rg cE < sZeBR

•Relativistic shock DSA (analogous argument):E < sZeBR

•All lead roughly to (Hillas):E < 0.9 Z BGauss Rpc ZeV


“Hillas Plot” for some plausible accelerators (after Hillas 1984)


Those estimates based on simple field models

Magnetic field amplification?For example, in shocks

(Bell & Lucek 2000)

Resonant wave instability:

202

20

2 ~~~

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Bv

PBMP

v

vBE

x

vxPvE

dx

dPv

dt

dE

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cA

w


Photo-pion production off Blackbody radiation

n =20 T3cm-3; E = 3.5x10-4T eV

Setting > R/c gives R < 1/(20T3)

Near threshold, E > 8x1019T-1 eV, cm-2; ~ 0.1

So propagation distance limited by

max(R, cacc) < 2.5x1026 cm (2.7/T)3 cm

Compact high luminosity accelerators probably eliminated:

*AGN (T~105K), R<0.3 AU for E>1014 eV *Near young neutron star (T ~ 3x107K), R<25 km for E>3x1012eV


Some Models: Radio Galaxy Jet Terminal Shock (e.g., Rachen & Biermann 1993)

us > 0.1c; a>0.1R ~ 10 kpcB ~ 10-5-4 G

•Hillas constraint applied to DSA give E ~ 1 ZeV; acc > 105 yr

•Synchrotron & photo-pion losses give comparable limit

•Shear layer of relativistic jet (eg, Ostrowski 2002, Rieger & Duffy 2004)(similar to DSA, except boost E/E ~ j, so can be quickin principle. Escape still limits to Hillas constraint.

•RGs rare in the local universe, so isotropy from RGs inside GZK sphere requires nanoGauss intergalactic and/or 100 nanoGauss galactic halo magnetic fields to deflect arrival directions.

•Jet proton content uncertain


BL Lac Jets

Possible correlation with BL Lacsrelativistic jets with ~ 10 beamed

our way

Local BLL density small, so same isotropy concerns already mentioned

If sources outside GZK sphere, then `X-bursts’,‘uhecrons’ ? (‘liberated’ superheavies, productsthat avoid or delay GZK)(Albuquerque etal 1998; Biermann & Frampton 2005)


Cosmic structure shocksKang, Rachen & Biermann 1997

shocks thermal emission

Shock surfaces Thermal Emissivity

Cluster shocks are big (~ Mpc), moderately fast (~103km/sec),but B is weak (~< G), so E < few EeV by various arguments(e.g., Norman, Melrose & Achterberg 1995;Ostrowski & Siemieniec-Ozieblo 2002)

~20Mpcbox


Larger shocks: sheets, filaments & ‘superclusters’

25h-1 Mpcbox

R ~ 10s of Mpcus ~ few 102

km/sec

B ~ 10-9-10-7 G?

E ~ 100 EeV ?

Not likely

Ryu, Kang, Hallman & Jones 2003


Gamma Ray Bursts:e.g., Waxman 1995, 2000; Vietri 1995

Ultrarelativistic shocks in fireballs (jets):~1052-53 erg>300, with internal shocks from flow variations

Waxman 1995, 1999: DSA at internal shocks; R < 1016 cmIf B in equipartition with radiation, B~104 Gauss

E < ZeBR ~ 1020 eV(photopion losses not as restrictive,But synchrotron losses should limitE<1019 eV)Shock/Proton efficiency?Evolution constraints


GRB Blast Wave Model

e.g., Vietri 1995; Gallant & Achterberg 1999; Vietri, De Marco & Guetta 2003

•If in ISM, insufficient time to reach UHE (G & A):E < 5x1015 BG (E52 3/n0)1/3 eV,= E /Mc2

•If in a Pulsar Wind Bubble, thenB ~ 0.1-10 G for R ~ 1016 cmE < 1020 3

2 iW eV,W is spin down luminosity,i is the proton mass fraction

•Energetics: If no evolution, then GRB ~ UHE


Young Magnetar Winds

Arons (ApJ, 589, 871, 2003)

•Winds avoid large magnetospheric energy losses (Blasi, Epstein & Olinto 2000)~ 3x1022 33 (4)2 V available magnetic rotator voltage•Ion return current sheet may experience ~10% of •Wind can carry substantial fraction of spindown energy Spin down time ~ 5 I45/(33 4)2 minutes•Ions may ‘surf’ the wind•A fast magnetar birth rate ~ 10-5 /yr/galaxy & 10% efficiency for UHECR accounts for energetics•Injection spectrum ~ E-1 steepening to E-2 if early GR spindown•Is the wind dissipated in ejecta?


Summary:•UHECR spectrum extends at least beyond 100 EeV•Probably extragalactic & ‘light’ hadrons•Serious constraints on source physics and spatial distributions •Proposed astrophysical source models numerous•Common themes:

Strong, very fast shocks (relativistic)Strong shear (relativistic)Rapidly rotating, magnetized objects/relativistic winds

•All models require some ‘faith’ to get > ZeV, enough flux•New data (CR spectrum, isotropy, composition, & )

should trim/refine the list.


The End


Structure Shock Mach number distribution by upstream phase

Hot:T > 107 K

WHIM105 K< T < 107 K

‘External’shocks

Regions surroundingClusters containModerately strongShocks(unvirialized)

Hallman (UMN PhD thesis (2004))


Energy Extracted by CRs Could be Substantial

Hallman (UMN PhD thesis (2004))

Triangles: Thermal

Squares: CRs(nonlinear DSAModel fromRyu etal 2003)

Shock dissipation nearClusters (R < 1 h-1 Mpc)


Can Structure Shocks Accelerate UHECRs?

With standard diffusionassumptions (i.e, Bohm), DSA just too slow with likely fields to beat photopion losses above GZK

cTu

cr

s

g

320

1

23

20

Gauss7.2

1092

39

a

EeV

Z

E

K

TxB

Setting a < gives

or


Quasi-Perpendicular Shocks Might Beat This (?)

If MHD turbulence is weak ( = rg >> rg)and B perp to shock normal, then, cross-field diffusioncontrols DSA (Jokipii, (ApJ, 313, 842 ( 1987)): perp (1/2) par, where < (c/us)

a ~ (1/ 2) a (Bohm) << a (Bohm)

Kang, Rachen & Biermann (MNRAS, 286, 257 (1998))

Additional constraints: diffusion along B (escape)Ostrowski & Siemieniec-Ozieblo (A&A 386, 829 (2002),

Or requiring rg < Rshock.Both basically return the Hillas constraint, soB » G (clusters) B » 100 nG (filaments)


Turbulent, 2nd Order Acceleration

Very likely present, but generally slower than DSA

For strong Alfvenic turbulence, compared to strong shock DSA

a(2nd order) ~ (us/vA)2 a(DSA) » a(DSA)


HiRes Collab ‘02


‘Dead Quasars’

Boldt & Ghosh 1999Levinson 2000

•Quasars rare today• However, most galaxies host SMBH•‘Dead’ or ‘underfed’ AGNs•B & G estimate > ten 109 Msun SMBH within 50 Mpc•~ 2x10-5 Mpc-3; L ~ 1042 erg/sec

•Model: Extraction of rotational energyvia BZ-induced magnetic field: emf ~ 1021 V (109 Msun)•Curvature radiation reduces limit > order of magnitude

•Details not available

Astrophysical Sources of UHECRs

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