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

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 astronomy: Point source sensitivity 1) Point-like sources 2) Diffuse fluxes with detectors with large FOV (HAWC, LHAASO, HiSCORE …): HAWC  g -rays from c.r. interactions  g -rays associated to the ICECUBE neutrinos ? CTA-North CTA-South LHAASO Absorption of gamma rays in the Galaxy by pair production with target radiation fields S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Attenuation of the gamma ray flux by pair production g + g e + e - Cross section Gamma ray energy threshold: 2𝑛𝑓 2 = E 𝛿 𝜁 (1−𝑑𝑝𝑡𝜄) Maximum cross section for: 1.02 (1−𝑑𝑝𝑡𝜄) E TeV 𝜁 eV = 4𝑛𝑓 2 = 𝐹 𝛿 𝜁 (1 − 𝑑𝑝𝑡𝜄) 𝑡 𝑦 = 4𝑛𝑓 2 Flux attenuation: 𝐹 = gamma ray energy 𝐺 = 𝐺 0 𝑓𝑦𝑞 (−𝜐 E , 𝑦 ) 𝜁 = target photon energy q = angle between photons S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Absorption of gamma rays in the Galaxy Photon number density vs. energy Radiation fields in the Galaxy: CMB Extragalactic components DUST uniform and isotropic CMB PeV g -rays • • EBL (negligible absorption) STARLIGHT Galactic components anisotropic and of increasing intensity EBL towards the Galactic center Infrared data Dust IR ≈ 100 TeV g -rays • COBE Starlight ≈ 1 TeV g -rays • IRAS S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Survival probability vs. gamma ray energy Absorption for 3 source positions Tables with absorption coefficients are available at IR www.silviavernetto.it/data.html absorption  E g from 1 TeV to 100 PeV CMB  Different gamma ray arrival directions absorption  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 S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

High energy Galactic diffuse gamma ray emissions  ‘‘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 35 th ICRC, 12-20 July 2017, Busan, Korea

Galactic diffuse gamma ray flux Galactic diffuse g -rays are produced by cosmic ray (nuclei & electrons) interactions with the interstellar matter and radiation: Fermi LAT  p 0 decay  Inverse Compton E g > 1 GeV  Bremsstrahlung Image Credit: NASA/DOE/Fermi LAT Collaboration S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Galactic diffuse gamma ray flux data from the Northern emisphere |b| < 5° Cosmic rays all particle flux × 10 -4 ? ? ? S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

‘‘ 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 [ p 0 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 35 th ICRC, 12-20 July 2017, Busan, Korea

A simple phenomenological model to describe the Galactic diffuse gamma ray emission Gamma ray flux (10-100 GeV) Emission spatial distribution Gal. latitude Exponential model distribution −𝑆 |𝑎| q g 𝑆, 𝑎 = 𝐷 exp ( 𝑆 0 - 𝑎 0 ) Fermi data Exponential model R 0 = 3.9 kpc Z 0 = 0.27 kpc Gaussian model determined by fitting the Fermi angular distribution for E > 10 GeV Gal. longitude Z distribution R Fermi data Exponential model Gaussian model S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Absorption of the Galactic diffuse flux The flux attenuation depends on the direction of gamma rays Survival probability for E = 100 TeV P S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Expected Galactic diffuse gamma ray flux Grey band: expected gamma ray flux in the region |lat| < 5° long =25°-100° 1 year LHAASO Unabsorbed 5 sigma flux sensitivity (approximate) S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Gamma rays & IceCube neutrinos Are neutrinos Galactic or HESE neutrinos extragalactic ? Fermi Neutrino flux diffuse (from upgoing muons) gamma rays Icecube neutrino angular distribution Angle integrated flux is consistent with isotropy Neutrino emission is usually accompanied by a gamma ray emission of similar intensity and spectral shape. Extragalactic gamma rays would be completely absorbed . But if a significant fraction of neutrinos is Galactic, the associated gamma ray flux can be observed. S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos 1 - Dark Matter model (Esmaili & Serpico, 2015) Neutrinos are produced in the decay of a heavy DM particle Space distribution of emission points 𝑠 0 r 𝑠 = 2 r c = 20 kpc (spherical simmetry around GC ) 𝑠 1+ 𝑠 𝑠 𝑑 𝑠 𝑑 Angular distribution of the emission points S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos 2 – Extended halo model (Taylor, Gabici & Aharonian, 2014) Neutrinos are produced by c.r. interactions in an extended halo −𝑠 2 r 𝑠 = exp ( 0 ) Space distribution of emission points 2𝑠 2 𝑠 0 = 57 kpc (spherical simmetry around GC ) < 𝑠 2 > = 100 kpc Angular distribution of the emission points S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

Possible Galactic gamma ray emissions associated to ICECUBE neutrinos 3 – Fermi Bubbles (Lunardini et al., 2014) Neutrinos are produced in the Fermi Bubbles 2 spheres of radius R = 3.9 kpc Space distribution of emission centered at x = y = 0, z = ±5.5 kpc points r (r) = 1 / sqrt (1 – r 2 / R 2 ) r = distance from the sphere center Angular distribution of the emission points S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

All models – Distance distribution & gamma ray average survival probability Distance distribution of g -ray flux Average survival probability of gamma rays (before absorption) Energy (TeV ) S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

1) Dark Matter decay 2) Extended c.r. halo HESE neutrino flux (isotropic ) Unabsorbed gamma rays DM gamma rays + absorbtion Large halo gamma rays CASA MIA, 1997 + absorbtion KASCADE, ICRC 2003 S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea

3) Gamma rays from the Fermi Bubbles No neutrino excess Fermi is observed from the gamma rays HAWC gamma ray U.L. Fermi Bubbles HESE neutrino flux (isotropic ) Hypotetical gamma ray flux 1 y LHAASO Absorbed sensitivity gamma ray flux (approximate) S.Vernetto & P.Lipari 35 th ICRC, 12-20 July 2017, Busan, Korea