Observational Cosmology through high andvery high energy gamma rays
Daniel Mazin
Institute for Cosmic Ray Research, University of Tokyo
Max Planck Institute for Physics, Munichmazin@icrr.u-tokyo.ac.jp

ASJ Meeting, KONAN University, 9 September 2015
1Outline
Extragalactic Background
Light (EBL)
Indirect methods tomeasure EBL
Instruments to measure
HE/VHE gamma rays
Limits by Fermi-LAT
Limits by Imaging
Cherenkov Telescopes
Future perspective: CTA
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

2AGN

HE/VHE ϒ-Rays

Nikishov (1962), Jelley (1966), Gould & Schreder (1966)

Stars and Dust
in Galaxies

AGN

HE/VHE ϒ-Rays
UV/O/IR
Photons

Nikishov (1962), Jelley (1966), Gould & Schreder (1966)

Stars and Dust
in Galaxies

AGN

HE/VHE ϒ-Rays
UV/O/IR
Photonsee+

Nikishov (1962), Jelley (1966), Gould & Schreder (1966)

Stars and Dust
in Galaxies

intrinsic
dN/dE

AGN

EnergyHE/VHE ϒ-Rays
UV/O/IR
PhotonsdN/dE

measuredee+EnergyNikishov (1962), Jelley (1966), Gould & Schreder (1966)

Stars and Dust
in Galaxies

intrinsic
dN/dE

AGN

EnergyHE/VHE ϒ-Rays
UV/O/IR
PhotonsdN/dE

measuredPair production:
γTeV γEBL ➞ e+ e2 2ee+Energy

2E EEBL ⇡ 4(me c ) ⇡ 1 MeV
EEBL ⇠ eV ! E ⇠ TeV
Nikishov (1962), Jelley (1966), Gould & Schreder (1966)

Stars and Dustin Galaxies

intrinsic
dN/dE

AGN

EnergyHE/VHE ϒ-RaysUV/O/IR
Photons

Constrain the EBL density- Measured spectrum + assumptions about theUnique information- Strong foregrounds hamper direct measurements- Redshift resolved- True integrated measurement
Stecker, de Jager 1992, Aharonian et al 2006, Mazin & Raue 2007 ...

dN/dE

intrinsic spectrum- Many sources at different redshifts to disentangle
eEBL and intr. spectrume+measuredEnergyStars and Dust
in Galaxies

AGN

HE/VHE ϒ-RaysUV/O/IR
Photonsee+Santos et al. 2002, Fernadez & Komatsu 2006, Raue, Kneiske, Mazin
2009, Gilmore 2011, Raue & Meyer 2012, ...

Stars and Dust
in Galaxies

AGN

HE/VHE ϒ-Rays
UV/O/IR
Photons

Investigate EBL sources- Star & dust in galaxies- Population III stars- Exotic contributions
Study star formation rate density- Structure formation history

Santos et al. 2002, Fernadez & Komatsu 2006, Raue, Kneiske, Mazin
2009, Gilmore 2011, Raue & Meyer 2012, ...

ee+Stars and Dust
in Galaxies

AGN

UV/O/IR
Photonse+

Coppi & Aharonian 1997, Aharonian et al. 2002, Neronov & Vovk 2010,
Tavecchio et al. 2011, Taylor et al. 2011, ..

e-Stars and Dust
in Galaxies

AGN

UV/O/IR
Photonse+

Coppi & Aharonian 1997, Aharonian et al. 2002, Neronov & Vovk 2010,
Tavecchio et al. 2011, Taylor et al. 2011, ..

e-Stars and Dust
in Galaxies

AGN

UV/O/IR
Photonse+e-e+
Coppi & Aharonian 1997, Aharonian et al. 2002, Neronov & Vovk 2010,
Tavecchio et al. 2011, Taylor et al. 2011, ..

e-Stars and Dust
in Galaxies

AGN

UV/O/IR
Photons

e+e-Magnetic Fieldse+Coppi & Aharonian 1997, Aharonian et al. 2002, Neronov & Vovk 2010,
Tavecchio et al. 2011, Taylor et al. 2011, ..

e-Stars and Dust
in Galaxies

AGN

Study intergalactic magnetic
field (IMG)- Extremely difficult to measuree-directly, only weakly constrained- Pair halos- Pair cascades
UV/O/IR
Photons

e+e+e-

Magnetic Fieldse+Coppi & Aharonian 1997, Aharonian et al. 2002, Neronov & Vovk 2010,
Tavecchio et al. 2011, Taylor et al. 2011, ..

e-Stars and Dust
in Galaxies

AGN

HE/VHE ϒ-Rays
UV/O/IR
Photons

Magnetic Fields

Raffelt & Stodolsky 1987; De Angelis et al. 2007; Mirizzi et al. 2007, ...

Stars and Dustin Galaxies

AGN

Axion like particles- Light shines through a wall
Conversion circumvents attenuation- (Often) depends on details of B

HE/VHE ϒ-Rays

Quantum gravity...

UV/O/IR
Photons

XA

Magnetic Fields

Raffelt & Stodolsky 1987; De Angelis et al. 2007; Mirizzi et al. 2007, ...

X

The EBL energy density: data
DM et al., APh, 43 (2013), 241

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

8

The EBL energy density: models
Dominguez et al., MNRAS 410, 2556 (2010)

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

9Imprint of the EBL on spectra of HE/VHE
gamma ray spectra of distant sources
Cross section of pair production:
peaks at ~4*Ethreshold
Delta function approximation is
not precise

Attenuation of Gamma-ray flux is
calculated by integrating over numberdensity of EBL, angles betweenphotons, and distance to the source.
The attenuation factor is sensitive tothe EBL density

Dominguez et al., MNRAS 410, 2556 (2010)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

10Indirect methods to measure theEBL: Sources
Typical extragalactic source at HE/VHE gamma rays is ablazar
blazarAGN

Factories of violent, broad band (up to highenergy) non-thermal radiation!
Blazars: relativistic plasma jet, highly variable!
TeV blazars (above 100 GeV): ~45 out of 55
are HBL (High-peaked BL Lacertae)
Daniel Mazin

Typical energy spectrum has a 2-bump structure!
First bump is synchrotron emission from electrons!
Second bump probably Inverse Compton (IC)from the same population of photons (SSC) orIC from external photon fields (EC)ASJ meeting, 9 September 2015, KONAN University

11

Indirect methods to measure theEBL: Assumptions
There is no pile-up at highest gamma rays energies
measured
PKS 2155-304

B

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN UniversityA

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Indirect methods to measure theEBL: Assumptions
There is no hardening of the energy spectrum between HEregime (typically measured by Fermi-LAT)and VHE regime measured by the imaging Cherenkov telescopes

DM et al, Aph 43, 241-251 (2013)
intrinsic (not affected by EBL)
Daniel Mazin

absorbed (affected by EBL

ASJ meeting, 9 September 2015, KONAN University

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Indirect methods to measure theEBL: Assumptions
The intrinsic energy spectrum is smoothno wiggles with correct EBL density

wiggles with in-correct EBL density
DM et al, Aph 43, 241-251 (2013)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Indirect methods to measure theEBL: Instruments
High energy gamma rays are measured by Fermi-LAT (also Agile)

100 MeV < E < 300 GeV
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Indirect methods to measure theEBL: Instruments
Very High energy gamma rays are measured by Imaging Atmospheric Cherenkov Telescopes (IACTs):
H.E.S.S., MAGIC and VERITAS (as well as Water Cherenkov Detectors (HAWC) which, however, have amuch worse energy resolution)

50 GeV < E < 100 TeV+30-30Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Indirect methods to measure theEBL: Instruments
Very High energy gamma rays are measured by Imaging Atmospheric Cherenkov Telescopes (IACTs):
H.E.S.S., MAGIC and VERITAS (as well as Water Cherenkov Detectors (HAWC) which, however, have amuch worse energy resolution)

50 GeV < E < 100 TeV

VERITAS

MAGIC

+30

HESS-30

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Limits from Fermi-LAT
Idea: F(E)observed = F(E)intrinsic ∙ exp(-b ∙ τmodel)
with b as a free parameter
F(E)intrinsic is extrapolated from measured spectrum in unabsorbed
energies to higher energies from the same data.
F(E)observed is measured spectrum.
τmodel is gamma-ray optical depth calculated from a given theoretical
EBL model
Expected result:b=0: there is no EBL
b=1: the EBL model is correct
Fermi-LAT, Science, 338, 1190 (2012)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Limits from Fermi-LAT
Average of the residuals with respect !
to the best fit models for all z<0.2 bin.

Assumption: BL Lac spectra follow
a parabolic shapeResiduals for best fit b are flat

Results: EBL is detected and consistent with state-of-the-art EBL models
Fermi-LAT, Science, 338, 1190 (2012)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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Limits from Fermi-LAT
EBL is detected and consistent with state-of-the-art EBL models

Fermi-LAT, Science, 338, 1190 (2012)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

19Limits from IACTs
Reminder: effect of EBL:H.E.S.S. from several sources
H.E.S.S., A&A 550, 11 (2013)

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ASJ meeting, 9 September 2015, KONAN University

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Limits from IACTs
MAGIC from single sources
MAGIC, Science 320,1752 (2008)

MAGIC, submitted (2015)preliminary

Using data from 3C 279 (z=0.536)
Daniel Mazin

Using data from 1ES1011+496 (z=0.211)

ASJ meeting, 9 September 2015, KONAN University

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Limits from IACTs
Combined results from many sources and data from
diﬀerent experiments makes results more robust
Biteau&Williams, arXiv:1502.04166

Meyer, DM,++ A&A 542 A59 (2012)

EBL detection

Stringent upper limits

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

22Cosmology: Hubble parameterOnce EBL is known, the imprint of the EBL on VHE spectra ofAGNs can be used to independently estimate their distanceDominguez++, ApJ 770, 77 (2013)

Biteau&Williams, arXiv:1502.04166

H0=( 71.8+4.6-5.6 (stat) +7.2-13.8 (syst)) km/s/Mpc

H0= (88 +/-8 (stat) +/- 13 (syst)) km/s/Mpc

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University23

10 fold sensitivity of current instruments
10 fold energy range
improved angular resolution
two sites (North / South)
operated as observatory

The future inVHE gamma ray
astronomy:!

World-wide cooperation
27 countries
150 institutes>1200 scientists

Topic of this session

Future prospects: CTA
CTA will have two observatories, North and South,
cover 20 GeV to >300 TeV, survey capabilities
sensitivity vs energy

sensitivity vs time at low energies

Plots from Funk&Hinton, AP 43, 348-355 (2013)
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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CTA: Key Science Projects
Three of 10 KSPs will deal (at least partially) with EBL and IGMF:
AGN survey:
obtain high quality spectra of ~50 bright blazars at diﬀerent z
extensive Target of Opportunity program
GRBs: chance to obtain high quality signal from z>1 (actually there is noupper limit on z)
Extragalactic survey: find new hard spectra GeV-TeV sources
6040Fermi/LAT

CTA exposure
for AGN survey

200-20Detectabl

AGNs detgalactic latitude (deg)

80

hours

+90°+180°-40-180°

AGNs in CTA ExG

144 extragal. sources
486 galactic sources

Sources CTA Gal

Sources in Fermi/-60

AGNs detected by-80-90°

galactic longitude (deg)Time distribution for extragalactic KSPs
Daniel Mazin

CTA Galactic and extragalactic surveys

ASJ meeting, 9 September 2015, KONAN University

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Future prospects: CTA
CTA can measure the evolution of the EBL,
which can help constraining the star and galaxy evolution
scenarios
sensitivity of CTA to resolve EBL evolution

Star formation rate is notwell determined at z>1

EBL scaling factor

HESS limits
Fermi/LAT limits

2

CTA prediction

1.8
1.6
1.4
1.2
1
0.8
0.6
0.4

preliminary

0.2
00

0.2

0.4

0.6

0.8

1DM, in preparation
Daniel Mazin

1.2

1.4

1.6

1.8
2
redshift z

Horiuchi & Beacom, ApJ 723,
329-341 (2010)

ASJ meeting, 9 September 2015, KONAN University27

Conclusion
EBL can be constrained and detected indirectly with Fermi/LATand Imaging Cherenkov Telescopes
Derived limits are consistent with the EBL from resolved
sourceswhich means that the current limits and measurements suggestthat at z=0 there is no significant contribution to the EBL byunresolved sources
Some pile-ups at high energies in the spectra of blazars are
intriguing but not significant yet (could be a sign of axion-likeparticles)
CTA will be an eﬀective machine to resolve EBL evolution to z=2
Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University

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BACKUP29

Limits from IACTs: axions
Contradicting results:
J. Biteau & D. Williams (2015) vs. D. Horns & M. Meyer (2012)

Daniel Mazin

ASJ meeting, 9 September 2015, KONAN University30