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Hard X-Rays & Gamma-Rays Induced by
Ultra High Energy Proton Accelerationin Cluster Accretion Shocks
Susumu InoueFelix AharonianNaoshi Sugiyama (NAO Japan)
accretion(inc. minor merger)
p acceleration to E~1018-19 eV-> p+CMB→ p+ e+e- E~1015-16 eV-> e+e-+B(~G)→syn. E~101-3 keV e+e-+CMB→IC E~TeV
(MPIK Heidelberg)
paper in prep.
shock formation in clustershierarchical, dark matter-driven structure formation→ merger & accretion shocks→ gas heating+ nonthermal particle acceleration→ nonthermal radiation
accretion(minor merger)
e.g. Ryu et al. 03
strong (high M) shock
nonthermal high energy emission from clusters
Miniati ‘03
thermal >100 MeV>100 keV
• primary electron IC
• LE proton p+p->0
• UHE proton-induced pair syn.+ICc.f. Aharonian 02 Rordorf et al. 04
traces shock
traces gas
e.g. Waxman & Loeb 00 Gabici & Blasi 03
e.g. Dar & Shaviv 95 Völk et al. 96 Berezinsky et al. 97
11
10
9
8
720.520.019.519.018.518.017.5
log E [eV]
maximum proton energy in accretion shocks
accel. vs CMB/adiabatic losses
photopion
adiab.
accel.Bs=0.1 G
photopair
c.f. G.Farrar’s talk
e.g. Kang, Ryu & Jones 96 Kang, Rachen & Biermann 97
accel.Bs=1 G
Rs~3.2 MpcVs~2200 km/s
e.g. Coma-like clusterM=2x1015 M(T=8.2 keV)WMAP cosmo. parameters
Bs,eq~ 6 G
Emax~1018-1019 eV
tacc,Bohm=(20/3) rgc/Vs2
shock radius, velocity, etc.
Bohm limit accel.
SNR observationse.g. Bamba et al. 04
proton injection luminosity in accretion shocks
accretion rate & luminosityM(M,z)=fgasfaccVs
3/GLacc(M,z)=fgasfaccGMM/Rs
~2.7*1046 (fgas/0.16) (facc/0.1) erg/s
proton luminosity & spectrumLp(M,z)=fpLacc(M,z) fp=0.1Fp(E,M,z) E∝ -2 exp(-E/Emax)
facc=0.1 normalization from simulation Keshet et al. ‘04
secondary production and emission processesp+CMB→ p+ e+e-
Ep~1018eV E+-~+-Ep~1015eV, L+-~t+-/tinj f(E>1017.7eV) Lp
→ e+e-+B(~G)→ syn. E~keV-MeV e+e-+CMB→ IC E~TeV-PeV
Aharonian 02 code solve pair kinetic eq.
..
emitted luminosity Coma-like cluster
- large radiative efficiency from protons- hard (~-1.5) spectrum
44
43
42
41
40
39151050
log E [eV]
Lp=2x1045
erg/s
Tinj=2x109 yr, R=3 Mpc
n=10-6
cm-3
B=0.1 (G Ep=8 10x 17 )eV
=0.3 B (G Ep=2.5 10x 18 )eV
=1 B (G Ep=8 10x 18 )eV
e+e- syn
e+e- IC
pp0 ( 10)x
emitted flux > TeV absorption by IRB, CMB
Coma-like cluster at D=100 Mpc
-15
-14
-13
-12
-11
-10
14121086420 log E [eV]
e+e- syn
Lp=2x1045
erg/s
Tinj=2x109 yr, R=3 Mpc
n=10-6
cm-3
D=100 Mpc
B=0.1 (G Ep=8 10x 17 )eV
=0.3 B (G Ep=2.5 10x 18 )eV
=1 B (G Ep=8 10x 18 )eV
pp0 ( 10)x
e+e- IC
emitted flux
extended source sensitivity x (~3 deg/ang. res.)
Coma-like cluster at D=100 Mpccaution: point source sensitivities
-15
-14
-13
-12
-11
-10
14121086420 log E [eV]
e+e- syn
Lp=2x1045
erg/s
Tinj=2x109 yr, R=3 Mpc
n=10-6
cm-3
D=100 Mpc
B=0.1 (G Ep=8 10x 17 )eV
=0.3 B (G Ep=2.5 10x 18 )eV
=1 B (G Ep=8 10x 18 )eV
GLAST
HESS
5 5@
INTEGRAL
HXD
NeXT 5 5HXI 'x '
NeXTSGD
pp0 ( 10)x
e+e- IC
model vs Coma data
perhaps not impossible? but need optimismradio something else
-15
-14
-13
-12
-11
-10
-9
151050-5
log E [eV]
Lp=4*1046
erg/s
Tinj=2*109 yr, R=3 Mpc
n=10-6
cm-3
B=1 (G Ep=4.5*1018 )eV=100 D Mpc
EUVE
RXTEBSAX
EGRET
GLAST5 5@
HESS
INTEGRAL
HXD
NeXT 5 5HXI 'x '
NeXTSGD
implications
UHE p-induced emission in cluster accretion shocks
• probe of UHE proton acceleration• probe of accretion shock• probe of magnetic field at cluster outskirts• probe of IR background
summary
• acceleration to E~1018-1019eV plausible• efficient secondary pair production and emission -> sync. (hard X-MeV) detectable by ASTRO-E2/HXD, imagiable by NeXT -> IC (TeV) detectable by HESS and other current IACTs
UHE p-induced emission in cluster accretion shocks
• contribution to extragalactic gamma background• nonlinear effects in proton acceleration• …
more efficient than primary IC, p-p 0
next steps