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The Galactic diffuse gamma ray emission in the energy range 30 TeV 3 - - PowerPoint PPT Presentation

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The Galactic diffuse gamma ray emission in the energy range 30 TeV 3 PeV Silvia Vernetto & Paolo Lipari Mount Rainier by Will Christiansen 35 th ICRC 12-20 July 2017 - Busan - South Korea Gamma ray astronomy at E > 30 TeV Galactic

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SLIDE 1

The Galactic diffuse gamma ray emission in the energy range 30 TeV – 3 PeV

Mount Rainier by Will Christiansen

Silvia Vernetto & Paolo Lipari

35th ICRC 12-20 July 2017 - Busan - South Korea

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SLIDE 2

Gamma ray astronomy at E > 30 TeV

LHAASO

Galactic astronomy: 1) Point-like sources 2) Diffuse fluxes with detectors with large FOV (HAWC, LHAASO, HiSCORE…):

  • g-rays from c.r. interactions
  • g-rays associated to the

ICECUBE neutrinos ? Absorption of gamma rays in the Galaxy by pair production with target radiation fields

Point source sensitivity

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea CTA-South CTA-North HAWC

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SLIDE 3

𝑦 = 𝑑 4𝑛𝑓2 = πΉπ›Ώπœ (1 βˆ’ π‘‘π‘π‘‘πœ„) 4𝑛𝑓2

E𝛿

=

2𝑛𝑓2 𝜁 (1βˆ’π‘‘π‘π‘‘πœ„)

ETeV 𝜁eV =

1.02 (1βˆ’π‘‘π‘π‘‘πœ„)

Attenuation of the gamma ray flux by pair production g + g e+ e-

Cross section Gamma ray energy threshold: Maximum cross section for:

𝐺 = 𝐺0 π‘“π‘¦π‘ž (βˆ’πœ E, 𝑦

)

𝐹 = gamma ray energy 𝜁 = target photon energy q = angle between photons

Flux attenuation:

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

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SLIDE 4

Absorption of gamma rays in the Galaxy

CMB EBL

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

DUST

STARLIGHT

Infrared data COBE IRAS

Photon number density vs. energy Radiation fields in the Galaxy:

Extragalactic components uniform and isotropic

  • CMB PeV g-rays
  • EBL (negligible absorption)

Galactic components anisotropic and of increasing intensity towards the Galactic center

  • Dust IR β‰ˆ 100 TeV g-rays
  • Starlight β‰ˆ 1 TeV g-rays
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SLIDE 5

Survival probability vs. gamma ray energy

Absorption for 3 source positions

CMB absorption IR absorption

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Tables with absorption coefficients are available at www.silviavernetto.it/data.html

  • Eg from 1 TeV to 100 PeV
  • Different gamma ray arrival directions
  • Source distance up to 30 kpc from GC

Absorption of very high energy gamma rays in the Milky Way S.Vernetto & P.Lipari, Phys.Rev. D 94, 063009, 2016

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SLIDE 6

High energy Galactic diffuse gamma ray emissions

  • β€˜β€˜Standard’’ diffuse flux

produced by cosmic ray interactions in the Galactic disk

  • Possible diffuse gamma rays models inspired by ICECUBE results

1) Dark matter decay 2) Extended c.r. halo 3) Fermi Bubbles

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

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SLIDE 7

Galactic diffuse gamma ray flux

Image Credit: NASA/DOE/Fermi LAT Collaboration

Galactic diffuse g-rays are produced by cosmic ray (nuclei & electrons) interactions with the interstellar matter and radiation:

  • p0 decay
  • Inverse Compton
  • Bremsstrahlung

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Fermi LAT Eg > 1 GeV

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SLIDE 8

Galactic diffuse gamma ray flux data from the Northern emisphere

Cosmic rays all particle flux Γ— 10-4

|b| < 5Β°

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

? ? ?

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SLIDE 9

β€˜β€˜Conventional’’ diffuse emission model

Construction of a model based on the extrapolation of Fermi measurements:

  • Assumption 1: most of the diffuse gamma ray emission is generated by

the hadronic mechanism [p0 decay dominant channel of production]

  • Assumption 2: the cosmic ray spectral shape is equal in all points in the

Galaxy

  • Model for hadronic interactions based on Sibyll
  • The space distribution of the emission is inferred from the Fermi

angular distribution for E > 10 GeV

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

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SLIDE 10

A simple phenomenological model to describe the Galactic diffuse gamma ray emission

qg 𝑆, π‘Ž = 𝐷 exp (

βˆ’π‘† 𝑆0 - |π‘Ž| π‘Ž0 )

Exponential model

R0 = 3.9 kpc Z0 = 0.27 kpc

Gamma ray flux (10-100 GeV)

  • Gal. latitude

distribution

  • Gal. longitude

distribution

Fermi data Exponential model Gaussian model Fermi data Exponential model Gaussian model

Emission spatial distribution

Z R

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

determined by fitting the Fermi angular distribution for E > 10 GeV

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SLIDE 11

Absorption of the Galactic diffuse flux

The flux attenuation depends on the direction of gamma rays

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

P

Survival probability for E = 100 TeV

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SLIDE 12

Expected Galactic diffuse gamma ray flux

Unabsorbed flux Grey band: expected gamma ray flux in the region |lat| < 5Β° long =25Β°-100Β°

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

1 year LHAASO 5 sigma sensitivity (approximate)

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SLIDE 13

Gamma rays & IceCube neutrinos

HESE neutrinos Neutrino flux (from upgoing muons) Angle integrated flux Fermi diffuse gamma rays

But if a significant fraction of neutrinos is Galactic, the associated gamma ray flux can be observed. Icecube neutrino angular distribution is consistent with isotropy Neutrino emission is usually accompanied by a gamma ray emission of similar intensity and spectral shape. Are neutrinos Galactic or extragalactic ?

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Extragalactic gamma rays would be completely absorbed.

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SLIDE 14

1 - Dark Matter model (Esmaili & Serpico, 2015)

Neutrinos are produced in the decay of a heavy DM particle Space distribution of emission points (spherical simmetry around GC )

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

r 𝑠 =

𝑠0

𝑠 𝑠𝑑

1+ 𝑠

𝑠𝑑

2 rc = 20 kpc

Angular distribution

  • f the emission points
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SLIDE 15

2 – Extended halo model (Taylor, Gabici & Aharonian, 2014)

Neutrinos are produced by c.r. interactions in an extended halo Space distribution of emission points (spherical simmetry around GC )

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Angular distribution

  • f the emission points

r 𝑠 = exp (

βˆ’π‘ 2 2𝑠2

0 )

𝑠0 = 57 kpc < 𝑠2 > = 100 kpc

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SLIDE 16

3 – Fermi Bubbles (Lunardini et al., 2014)

Neutrinos are produced in the Fermi Bubbles Space distribution of emission points

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Angular distribution

  • f the emission points

2 spheres of radius R = 3.9 kpc centered at x = y = 0, z = Β±5.5 kpc r (r) = 1 / sqrt (1 – r2 / R2) r = distance from the sphere center

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SLIDE 17

All models – Distance distribution & gamma ray average survival probability

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

Distance distribution of g-ray flux (before absorption) Average survival probability

  • f gamma rays

Energy (TeV)

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SLIDE 18

1) Dark Matter decay 2) Extended c.r. halo

Large halo gamma rays + absorbtion DM gamma rays + absorbtion

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

HESE neutrino flux (isotropic ) Unabsorbed gamma rays

CASA MIA, 1997 KASCADE, ICRC 2003

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SLIDE 19

3) Gamma rays from the Fermi Bubbles

Absorbed gamma ray flux Hypotetical gamma ray flux

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

1 y LHAASO sensitivity (approximate) HESE neutrino flux (isotropic )

No neutrino excess is observed from the Fermi Bubbles

Fermi gamma rays HAWC gamma ray U.L.

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SLIDE 20

Conclusions

  • The gamma ray sky at energies > 30 TeV will be explored for the first time

by a new generation of high sensitivity gamma ray detectors.

  • The study of diffuse fluxes with wide fields of view instruments will be also of

great importance for the understanding of high energy processes in the Galaxy.

  • Gamma Ray absorption in the Galactic radiation fields must be carefully

considered, but does not preclude the study.

  • Telescopes with an effective area of 1 km2 and good rejection of c.r. background

should be able to measure the diffuse gamma ray flux generated by cosmic rays interactions in the Galaxy disk.

  • If the ICECUBE astrophysical neutrinos have a significant galactic component,

the associated gamma ray emission should be detectable in the next future.

S.Vernetto & P.Lipari 35th ICRC, 12-20 July 2017, Busan, Korea

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SLIDE 21

Backup slides

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SLIDE 22

SUN

GAL. CENTER

Infrared radiation model vs. data

Latitude distribution

100 mm 100 mm

Longitude distribution Infrared spectrum

Energy density at 100 mm

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SLIDE 23

Infrared radiation anisotropy

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SLIDE 24

Mean free path

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SLIDE 25

Survival probability: models comparison

Solid lines: our model Dotted lines: Moskalenko et al. Solid lines: our model Dotted lines: Esmaili & Serpico

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SLIDE 26

Diffuse Galactic gamma ray flux data

FERMI 100 MeV – 100 GeV All sky HESS E > 250 GeV l = -75Β° to 60Β° |b|< 2Β° (2014) ARGO-YBJ 0.3 - 1 TeV l = 25Β° to 100Β° |b|< 5Β° (2015) MILAGRO > 3.5 TeV l = 40Β° to 100Β° |b| < 5Β° (2005) 15 TeV l = 30Β° to 85Β° |b|<10Β° (2008) Above 100 TeV only upper limits: BASJE, EASTOP, UMC... The lowest are: CASA-MIA 140-1300 TeV l = 50Β° to 200Β° |b|< 2Β°,5Β°,10Β° (1996)