Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

From gamma rays to cosmic rays, to EBL and IGMFs• Secondary gamma rays from line-of-sight interactions of cosmic rays can be responsible
for hard spectra of distant blazars• Spectra robust, show remarkable agreement with data
• A broad range of EBL models agree with the data
• Extragalactic magnetic fields
Based on work in collaboration with Felix Aharonian, Shin’ichiro Ando, John Beacom,
Warren Essey, Yoshiyuki Inoue, Oleg Kalashev, Shigehiro Nagataki, Anton Prosekin
Astropart.Phys. 33 (2010) 81, ibid. 35 (2011) 135; Phys. Rev. Lett. 104 (2010) 141102;
ApJ 731 (2011) 51; ApJ Lett. 751 (2012) L11; ApJ 757 (2012) 183 ; PR D 87, 063002(2013); Phys.Rev.Lett. 111 (2013) 041103; arXiv:1308.5710
see also related work by Dermer, Finke, Migliori, Murase, Razzaque, Takami

1Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

−2 −1

dN/dE (GeV cm s )10-12−1-2-1dN/dE [ cm s TeV-1 ]Gamma-ray observations of distant blazars:
1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)-131010-14-15

1010-16

110Energy [ TeV ]10−1210−1310−14
10−1510−16
10−17100

200

500

1000E(GeV)

2000

5000

HESS (black), MAGIC (blue) and VERITAS (red) data points

2Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

−2 −1

dN/dE (GeV cm s )10-12−1-2-1

dN/dE [ cm s TeV-1 ]Gamma-ray observations of distant blazars:
1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)-131010-14-15

1010-16

110Energy [ TeV ]10−1210−1310−14
10−15
10−16
10−17100200500

1000
E(GeV)

2000

5000

HESS (black), MAGIC (blue) and VERITAS (red) data points
Theory, e.g., Stecker, et al. (1992): ...“we predict a sharp cutoff between 0.1 and 1 TeV”

2

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

−2 −1

dN/dE (GeV cm s )10-12−1-2-1

dN/dE [ cm s TeV-1 ]Gamma-ray observations of distant blazars:
1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)-131010-14-151010-16

110Energy [ TeV ]10−1210−13
10−14
10−15
10−16
10−17100

200

5001000E(GeV)

2000

5000

HESS (black), MAGIC (blue) and VERITAS (red) data points
Theory, e.g., Stecker, et al. (1992): ...“we predict a sharp cutoff between 0.1 and 1 TeV”

The data: no signs of absorption due to γγEBL → e+e−2

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Extragalactic background light (EBL)(direct and processed starlight)• intimately connected with star formation history and with dust content of the galaxies• models uncertain, but robust lower limits exist from star counts, especially for UV EBL
100
Madau & Pozzetti ’00 (HST)
Elbaz et al. ’02 (ISO)
Papovich et al. ’04 (Spitzer)
Fazio et al. ’04 (Spitzer)
Xu et al. ’05 (GALEX)
Dole et al. ’06 (Spitzer)
Frayer et al. ’06 (Spitzer)
Gardner et al. ’00 (HST)
Berta et al. ’11 (Hershel/PEP)
Wright & Reese ’00 (DIRBE)
Wright ’04 (DIRBE)
Levenson et al. ’07 (DIRBE)
Levenson & Wright ’08 (DIRBE)
Bernstein ’07 (HST)
Matsuoka et al. ’11 (Pioneer)
Matsumoto et al. ’11 (IRTS)
Matsuura et al. ’11 (AKARI)
Cambrésy et al. ’01 (DIRBE)
Dwek & Arendt ’98 (DIRBE)
Gorijian et al ’00 (DIRBE)
Finkbeiner et al ’00 (DIRBE)
Hauser et al ’98 (DIRBE)
Lagache et al ’00 (DIRBE)
Edelstein et al ’00 (Voyger)
Brown et al ’00 (HST/STIS)
Albert et al ’08 (MAGIC)

2νIν [nW/m /sr]

101γγEBL → e+e− should degrade
the energy of TeV photons

Baseline Model
Kneikse et al. ’04
Stecker et al. ’06
Franceschini et al. ’08
Gilmore et al. ’09
Finke et al. ’10
Kneiske & Dole ’10
Gilmore et al. ’120.1
0.1

110λ[µm]

1001000

10000

3Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

E2 dN/dE [erg/cm2/s]

Distant blazars have implausibly hard spectra

-5

10-6

10

1ES 0229+200(scaled)Γ = 2.40

10-7-810

1ES 1218+30.4(scaled)-9Γ = 1.30

10-10

10

1ES 1101+232

Absorption-corrected spectra are
extremely hard, Γ < 1.5, for distantblazars. [Aharonian et al.]

Γ = 1.28

10-11
10-12-13

10

10-1

110

E [TeV]

4

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Blazar spectra

correctedspectrum
MeasuredSpectranaive EBL
EBL−correctedspectra
10-1010-11

10-11

10-10-2

E2 dN/dE [TeV cm-2s-1]

10-10

E2 dN/dE [TeV cm s-1]

E2 dN/dE [TeV cm-2s-1]

Measured Spectra
measured
spectra10-1210-13

10-14
0.05

10-12

10-12

10-13

10-13

0.1

0.2

2 3 4 56
1E [TeV]1020 30

10-14
0.05

10-11

0.1

0.2

10-14
0.05

0.2
0.1
2 3 45
1
E [TeV]101

202 303 4 5 6

M. Errando

RGB_J0152+017
3C_66A
1ES_0229+200
1ES_0347-121
PKS_0548-322
RGB_J0710+591
S5_0716+714
1ES_0806+5241ES_1011+496
1ES_1101-232
Markarian_421
Markarian_180
1ES_1218+304
W_Comae
PKS_1424+240
H_1426+428
PG_1553+113
Markarian_501
1ES_1959+650
PKS_2005-489
PKS_2155-304
BL_Lacertae
1ES_2344+51420 30
10H_2356-309
E [TeV]

5

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Softening of the spectrum as a function of the redshift
3

DG

2

10-1

0.00

0.05

0.10

0.15
Redshift z

0.20

0.25

0.30

∆Γ = ΓGeV − ΓTeV [Stecker, Scully]

6

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Distant blazars are different:3Stecker−Scully

2.5δΓ21.5
1
0.5
000.1

0.2

0.3z

0.4

0.50.6δ Γ = ΓGeV − ΓTeV [Stecker, Scully]

7

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Proposed “new physics” solutions:
The lack of absorption prompted some exotic solutions:• photons may convert into some hypothetical axion-like particles that convert backinto photons in the galactic magnetic fields[Hooper et al.; de Angelis et al.; Simet et al.]
• Lorentz invariance violation for high-velocity particles may prevent pair production[Protheroe et al.]Is there a more conventional explanation?

8

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

AGN produce both cosmic rays and gamma rays

primaryγ

EBLe+e−secondary gamma raysp
B

CMB+EBL

CMB+EBL

9Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Cosmic rays from AGN• No significant attenuation below GZK cutoff.
< 1018 eV.
Propagate cosmological distances for E ∼• Rectilinear propagation affected only by IGMFs.
Clusters of galaxies (size R, density n) cause large deflections, but the mean free pathof a proton23Λ ∼ 1/(πR n) ∼ 3 × 10 Mpc
The mean MFP for linear propagation is of the order of the size of the observed
universe.
• IGMFs are not known:– upper limits: B < 10−9 G from non-observation of Faraday rotations– lower limits: B > 10−30 G if one believes the galactic fields are seed fields
amplified by dynamo.
For magnetic fields B < 10−14 G, deflections are smaller than the angular resolutionof ACTs.
10

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Secondary gamma rays from cosmic rays along the line of sight?
Gamma-rays produced at the source can attenuate via pair production on EBL for TeV
energies: expect attenuation of TeV γ rays.
Protons below GZK cutoff interact with EBL, CMB and produce γ rays via
pγ → pe+ e− , pγ → pπ 0 : expect regeneration of TeV γ rays
Photon backgrounds provide opacity/sink for the former, source for the latter.
What is the scaling of these effects with distance?

11Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Different scaling

Fprimary,γ (d)∝Fsecondary,γ (d)=Fsecondary,ν (d)∝1exp{−d/λγ }d2i  1/d,pλγ h−d/λγ
1−e∝21/d2 ,4πd(Fprotons × d) ∝1.
d(1)for d ≪ λγ ,for d ≫ λγ .

(2)
(3)

12

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Different scaling

Fprimary,γ (d)∝Fsecondary,γ (d)=Fsecondary,ν (d)∝1exp{−d/λγ }d2i  1/d,pλγ h−d/λγ
1−e∝21/d2 ,4πd(Fprotons × d) ∝(1)for d ≪ λγ ,for d ≫ λγ .

1.
d(2)
(3)

For distant sources, secondary signals win

12Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Secondary photons and neutrinos from 1ES0229+200 (z = 0.14)
102

108 GeV
1010 GeV
1011 GeV

101

E2 dN/dE, eV cm-2s-1

100

10-1

10-2

10-3

10-4

10-5

10-6
101

102

103

104

105

106
107
E, GeV

108

109

1010

1011

1012

[Essey, Kalashev, AK, Beacom, PRL 104, 141102 (2010)]
13

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Robust spectral shapes explain the observed universality
102

Measured Spectra

108 GeV
1010 GeV
1011 GeV

10110-10E2 dN/dE [TeV cm-2s-1]

E2 dN/dE, eV cm-2s-1

100

10-1

10-210-3

10-410-11

10-1210-13

10-510-6 110102

103

104

105

106
107
E, GeV

108

109

1010

1011

1012

10-14
0.05

0.10.22 3 4 56
1E [TeV]1020 3014

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

PeV neutrinos discovered by IceCube consistent withsecondary spectrum
710610510410310210

1

100pγ
ν

2-1 -1

jE , eV cm s sr-1

1010-1101010121410E, eV

10161018[Kalashev, Kusenko, Essey, Phys.Rev.Lett. 111 (2013) 041103]
15

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

EBL models
Once the contribution from cosmic rays is included, the spectra are not very sensitive tothe level of EBL.
Models considered:”High” EBL: Stecker et al. (2006) ApJ, 648, 774
Models between low and high: Salamon & Stecker 1998; Kneiske et al. 2002, 2004;
Stecker et al. 2007; Franceschini et al. 2008; Horiuchi et al. 2009; Primack et al. 2009;
Gilmore et al. 2009; Razzaque et al. 2009; Finke et al. 2010.
“Low” EBL: Shaped as “high”, but at the level of 40% lower.
The range between “high” and “low” encompasses all models.

16Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

“Low“ EBL (left), ”high“ EBL (right)
101

101
Fermi limit

10−1

210−210−3 8
101ES 0229+200

E dN/dE (eV cm−2s−1 )100

2E dN/dE (eV cm −2s −1 )1ES 0229+200

91010101110E(eV)12101310100

Fermi limit

10−110−210−3 8101091010

1011

E(eV)

10121013

Both fit the data.
[Essey, Kalashev, AK, Beacom, ApJ 731 (2011) 51]

17

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

“Low“ EBL (left), ”high“ EBL (right)
101

101
1ES 0347+121

E dN/dE (eV cm −2s −1 )100

Fermi limit

10−1100

Fermi limit

10−110−2

210−22

E dN/dE (eV cm −2 s−1 )1ES 0347+121

10−3 81091010101110E(eV)

1210

1310

10−3 8101091010

1011

E(eV)

10121013

Both fit the data.
[Essey, Kalashev, AK, Beacom, ApJ 731 (2011) 51]

18

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

“Low“ EBL (left), ”high“ EBL (right)
101

101
1ES 1101+232

1ES 1101+232

E dN/dE (eV cm −2s −1 )100
10−1Fermi limit

10010−110−2210−22E dN/dE (eV cm −2s −1 )Fermi limit

10−3 81091010101110E(eV)

1210131010−3 8101091010

1011

E(eV)

10121013

Both fit the data.
[Essey, Kalashev, AK, Beacom, ApJ 731 (2011) 51]

19

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

“Low“ EBL vs ”high“ EBLSource
1ES0229+200
1ES0229+2001ES0347-121
1ES0347-121
1ES1101-232
1ES1101-232

Redshift
0.14
0.14
0.188
0.188
0.186
0.186

EBL ModelLowHighLowHighLow
High

Lp , erg/s
1.3 × 1043
3.1 × 1043
2.7 × 1043
5.2 × 1043
3.0 × 1043
6.3 × 1043

Lp,iso , erg/s
4.9 × 1045
1.1 × 1046
1.0 × 1046
1.9 × 1046
1.1 × 1046
2.3 × 1046

χ2
6.4
1.8
16.1
3.4
16.1
4.9

DOF
77669
9

Here we have assumed θjet = 6◦ (and Emax = 1011 GeV, α = 2.)[Essey, Kalashev, AK, Beacom, ApJ 731 (2011) 51]

20

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

PKS 1424+240 at z > 0.6z = 0.6z = 1.3-7-7

1 ´ 10E2dNdEHGeV cm-2 s-1LE2dNdEHGeV cm-2 s-1L

1 ´ 10-8

5 ´ 101 ´ 10-8
5 ´ 10-9

1 ´ 10-9
5 ´ 10-10

1 ´ 10-10
0.11101001000

410

5 ´ 10-8

1 ´ 10-8
5 ´ 10-9

1 ´ 10-9
5 ´ 10-10

1 ´ 10-10
0.11101001000

EHGeVL

EHGeVL[Essey, AK, arXiv:1310.3440]

21104

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Lower limits on UHECR and jet powers of TeV blazars

48101720κ = 2.2
κ = 2.5
κ = 2.7

L UHECR (erg/s)

10 - 10 eV
47

101ES 1426
46

10

1ES 0229

45

LUHECR = L syn

1ES 0347

1ES 1101

1ES 0347

1ES 1101

1053
1052

10

1ES 1426
1ES 0229

L jet (erg/s)

51

1050

1049

1048

109

LEdd (10 M sun)

47

1046

1045
5.0×1046

1.0×1046

1.5×1046

2.0×10L syn (erg/s)

46

2.5×1046

3.0×10[Razzaque, Dermer, Finke, ApJ, 745, 196 (2012)]
22

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Softening of the spectrum reflects the transition
from primary to secondary gamma rays
3
Stecker−Scully

2.5
2usenkoδΓEssey−K

1.5
1
0.5
00

0.1

0.2

0.3

z0.4

0.5

0.6

δ Γ = ΓGeV − ΓTeV

Observations: blazars at z > 0.15 show no variability for E > 1 TeV
23

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Spectra ⇒ B ∼ 10−15 Gauss

1ES 0229+200−2−1E dN/dE (eV cm s )101

Fermi upper limit100−1810 Gi(rmFe−1210e)

tivtaten−1510 G−1310 G
10−2
108

109

1010

1011

1012

1013

E(eV)

For line-of-sight interactions to explain the point sources, the IGMFs must be in the range:−17−141 × 10G < B < 3 × 10

G

[Essey, Ando, AK, Astropart. Phys, 35 (2011) 135; arXiv:1012.5313]
24

Alexander Kusenko (UCLA/Kavli IPMU)

Kyoto, 2013

Conclusions• AGN produce both cosmic rays and gamma rays ⇒ secondary gamma rays should
dominate the signals of distant sources for IGMFs of the order of a femtogauss orsmaller.
• Secondary photons from distant blazars produce robust predictions for the spectra, inexcellent agreement with the data.
• First evidence that AGN accelerate cosmic rays at least to 1017 eV.
• Spectra fit for both high and low EBL. Previously set limits do not hold, except under
the assumption of large IGMFs.
• IGMFs in the range 10−17 − 10−14 G are consistent with secondary interpretation (andwith everything else), opening a window for a broad range of EBL models.
• Implications for future ACT detectors, such as CTA: more sources, distant sources[Inoue et al., arXiv:1308.5710]

25