High Energy High Energy emission from the emission from the

Galactic CenterGalactic CenterJason YbarraJason Ybarra

The Galactic CenterThe Galactic Center

Contains a supermassive black holeContains a supermassive black hole

M = 3.6 × 10M = 3.6 × 1066 M M

3 main radio sources Sgr B, SgR C, 3 main radio sources Sgr B, SgR C, SgR ASgR A

Very dense molecular cloudsVery dense molecular clouds Supernova remnantsSupernova remnants

ObservationsObservations

INTEGRAL IBIS/ISGRIINTEGRAL IBIS/ISGRI

(20-400 keV)(20-400 keV) HESSHESS

(0.1-20 TeV)(0.1-20 TeV)

INTEGRAL observationsINTEGRAL observations

IBIS/ISGRI imagerIBIS/ISGRI imager 4.6 Ms total exposure time for 4.6 Ms total exposure time for

observations between 2003-2004 observations between 2003-2004 Range 20-400 keVRange 20-400 keV

(Bélanger et al 2006)

INTEGRALINTEGRAL

IBIS/ISGRI mosaic of GC in in the 20–40 keV range.

(Bélanger et al 2006)

INTEGRALINTEGRAL

20-30 keV

30-40 keV

40-56 keV

56-85 keV

(Bélanger et al 2006)

Spectrum of IGR Spectrum of IGR J17456−2901 J17456−2901

Red is the ISGRI data. Green is a power law fit with index Γ = 3.04 ± 0.08

(Bélanger et al 2006)

Spectrum of IGR Spectrum of IGR J17456−2901J17456−2901

1-10 keV from XMM-Newton. 20-400 keV from ISGRI

Spectrum

Low temp plasma (1 keV)

High-temp plasma (6.6 keV)

Power law Γ=1.51

6.4 keV Fe line

Power law Γ2=3.22

(Bélanger et al 2006)

Spectrum of IGR Spectrum of IGR J17456−2901J17456−2901

The two-temperature plasma component does a decent job of modeling the 1-10 keV spectrum, but cannot account for the emission flux > 20 keV

(Bélanger et al 2006)

Possible Sources?Possible Sources?

X-Ray TransientsX-Ray Transients Sgr A* flaresSgr A* flares Charged-Particle AccelerationCharged-Particle Acceleration

X-Ray TransientsX-Ray Transients

Large number of X-Large number of X-Ray transients Ray transients near Sgr A*near Sgr A*

4 within 304 within 30″″ of Sgr of Sgr A*A*

Light curves were Light curves were constructed from constructed from Chandra and Chandra and XMM-Newton dataXMM-Newton data

CXOGC J174535.5−290124

CXOGC J174540.0−290005

CXOGC J174540.0−290031

CXOGC J174538.0−290022

INTEGRAL

(Bélanger et al 2006)

X-Ray TransientsX-Ray Transients Contemporaneous Contemporaneous

XMM-Newton data XMM-Newton data for for J174540.0−290031 J174540.0−290031

Estimated flux ~ 5 x Estimated flux ~ 5 x 10103434 erg s erg s-1-1 is still an is still an order of magnitude order of magnitude too low.too low.

Spectrum of transient Spectrum of transient unlikely to be a pure unlikely to be a pure power law > 100 keVpower law > 100 keV

CXOGC J174535.5−290124

CXOGC J174540.0−290005

CXOGC J174540.0−290031

CXOGC J174538.0−290022

IGR J17456-2901

(Bélanger et al 2006)

Possible Sources?Possible Sources?

X-Ray TransientsX-Ray Transients Sgr A* flaresSgr A* flares Charged-Particle AccelerationCharged-Particle Acceleration Sgr A EastSgr A East

X-Ray FlaresX-Ray Flares

Flares occur on average once per Flares occur on average once per dayday

Average L ~ 10Average L ~ 103535 ergs s ergs s-1-1, but last for , but last for a few thousand seconds.a few thousand seconds.

The constant luminosity of IGR The constant luminosity of IGR J17456-2901 cannot result from J17456-2901 cannot result from successive flaressuccessive flares

(Bélanger et al 2006)

Possible Sources?Possible Sources?

X-Ray TransientsX-Ray Transients Sgr A* flaresSgr A* flares Charged-Particle AccelerationCharged-Particle Acceleration

Charged Particle Charged Particle AccelerationAcceleration

Perhaps same origin as the HESS Perhaps same origin as the HESS TeV sourceTeV source

The TeV emission is thought to come The TeV emission is thought to come from the acceleration of particles from the acceleration of particles (protons) to very high energies (protons) to very high energies

(Bélanger et al 2006)

Proton-Proton CollisionsProton-Proton Collisions

Accelerated protons are thought to collide with ambient protons

p

p

Proton-Proton CollisionsProton-Proton Collisions

Accelerated protons are thought to collide with ambient protons

p

p

p

p

π0

This interaction produces neutral pions

Proton-Proton CollisionsProton-Proton Collisions

p

p

p

p

π0

γ

γ

Neutral pions decay very quickly into two gamma rays

Proton-Proton CollisionsProton-Proton Collisions

p

p

n

p

π+

Proton-Proton CollisionsProton-Proton Collisions

p

p

n

p

π+

μ+

νμ

Proton-Proton CollisionsProton-Proton Collisions

p

p

n

p

π+

μ+

νμ

e+

νμ

νe

Secondary electrons and positrons can produce gamma-rays through bremsstrahlung or inverse Compton scattering

Diffuse EmissionDiffuse Emission

Belanger et al. (2006) argue that Belanger et al. (2006) argue that the emission is diffusethe emission is diffuse

1)1) Absence of variabilityAbsence of variability

2)2) Not detected by JEM-X (3′ Not detected by JEM-X (3′ resolution)resolution)

HESS HESS

High Energy Stereoscopic System High Energy Stereoscopic System (HESS)(HESS)

This is an array of 4 atmospheric This is an array of 4 atmospheric Cherenkov TelescopesCherenkov Telescopes

HESS HESS

High Energy Stereoscopic System High Energy Stereoscopic System (HESS)(HESS)

This is an array of 4 atmospheric This is an array of 4 atmospheric Cherenkov TelescopesCherenkov Telescopes

HESS detected a HESS detected a point-like source of point-like source of very-high energy very-high energy gamma rays a the gamma rays a the galactic center galactic center (HESS J1745-290).(HESS J1745-290).

Galactic center

SNR/Pulsar Wind Nebula

(Aharonian et al 2006)

The white contours The white contours indicate molecular indicate molecular gas traced by CS gas traced by CS emissionemission

The correlation The correlation between molecular between molecular material and the material and the faint faint γγ-ray -ray emission indicates emission indicates cosmic ray origincosmic ray origin

Galactic center

SNR/Pulsar Wind Nebula

(Aharonian et al 2006)

(Aharonian et al 2006)

Energy distributionEnergy distribution

The diffuse The diffuse material exhibits material exhibits the same power the same power law index as HESS law index as HESS J1745-290J1745-290

This suggests that This suggests that J1745-290 is the J1745-290 is the source of cosmic source of cosmic rays that slowly rays that slowly diffuse outdiffuse out

(Aharonian et al 2006)

What can accelerate the What can accelerate the particles?particles?

Two possibilities:Two possibilities:

1)1) Supernova Remnant Sgr A East Supernova Remnant Sgr A East

2)2) SMBH Sgr A*SMBH Sgr A*

Inverse Compton Inverse Compton scatteringscattering

If a high-energy photon and a low-If a high-energy photon and a low-energy electron interact, the energy electron interact, the electron receives energyelectron receives energy

If a low-energy photon and a high-If a low-energy photon and a high-energy electron interact, the photon energy electron interact, the photon will increase it energy.will increase it energy.

Inverse Compton Inverse Compton scatteringscattering

ΔEγ/Eγ = - Eγ / mec2

Average energy lost by the photon

Average energy gained by the photonΔEγ/Eγ = 4/3 β2 γ2

ΔEγ/Eγ = 4/3 β2 γ2 - Eγ / mec2

Inverse Compton Inverse Compton ScatteringScattering

(Hinton & Aharonian 2007)

Inverse Compton Inverse Compton ScatteringScattering

The magnetic field strength is fixed at 105 μG

(Hinton & Aharonian 2007)

Inverse ComptonInverse Compton

Solid line – very young source with B = 50μG, electron spectrum α =0.3

Dashed line – old source B = 110 μG, α =1.5

(Hinton & Aharonian 2007)

Dark Matter AnnihilationDark Matter Annihilation

Green - Minimal Supersymmetric Standard Model annihilation of 14 TeV neutralinos

Dark Matter AnnihilationDark Matter Annihilation

Blue – mixed final state, DM masses 6-30 TeV

SummarySummary

Two leading theoriesTwo leading theories

1.1. Gamma rays from accelerated Gamma rays from accelerated particle interactions (p-p → p + p + particle interactions (p-p → p + p + ππ00, , ππ0 0 → 2→ 2γγ ))

2.2. Inverse Compton scattering Inverse Compton scattering

ReferencesReferences

Aharonian et al (HESS Aharonian et al (HESS Collaboration) 2006, PRL, 97, Collaboration) 2006, PRL, 97, 221102221102

Belanger et al 2006, ApJ, 636, 275Belanger et al 2006, ApJ, 636, 275 Hinton, J. A. & Aharonian F. A. Hinton, J. A. & Aharonian F. A.

2007, ApJ, 657, 3022007, ApJ, 657, 302

Diffuse TeV Emission Diffuse TeV Emission from the Galactic Centerfrom the Galactic Center

Jason YbarraJason YbarraHigh Energy Astrophysics SeminarHigh Energy Astrophysics Seminar

April 30, 2008April 30, 2008

HESS detected a HESS detected a point-like source of point-like source of very-high energy very-high energy gamma rays at the gamma rays at the galactic center (HESS galactic center (HESS J1745-290).J1745-290).

Galactic center

SNR/Pulsar Wind Nebula

(Aharonian et al 2006)

Previously …

The white contours The white contours indicate molecular indicate molecular gas traced by CS gas traced by CS emissionemission

The correlation The correlation between molecular between molecular material and the faint material and the faint γγ-ray emission -ray emission indicates cosmic ray indicates cosmic ray originorigin

Galactic center

SNR/Pulsar Wind Nebula

(Aharonian et al 2006)

Energy distributionEnergy distribution

The diffuse material The diffuse material exhibits the same exhibits the same power law index as power law index as HESS J1745-290HESS J1745-290

This suggests that This suggests that J1745-290 is the J1745-290 is the source of cosmic rays source of cosmic rays that slowly diffuse outthat slowly diffuse out

(Aharonian et al 2006)

Can protons accelerated by Sagittarius A* account for the diffuse emission seen by HESS?

SimulationsSimulations

Distribution of molecular cloudsDistribution of molecular clouds Magnetic field modeled with Kolmogrov Magnetic field modeled with Kolmogrov

turbulenceturbulence

Wommer et al. 2008 (arXiv:0804.3111v1 [astro-ph] 18 Apr 2008)

Energy loss ratesEnergy loss rates

p-p scattering p-p scattering p-p-γγ scattering scattering Synchrotron coolingSynchrotron cooling Compton scatteringCompton scattering

(Wommer et al. 2008)

Energy loss ratesEnergy loss rates

p-p scattering

Compton scattering

Synchrotron cooling Cooling rates within the clouds

(Wommer et al. 2008)

Energy loss ratesEnergy loss rates

p-p scattering

Compton scattering

Synchrotron cooling Cooling rates between the clouds

(Wommer et al. 2008)

Proton propagationProton propagation

F = qv × BF = qv × B Diffusion equationDiffusion equation

1,000 protons were followed with the 1,000 protons were followed with the Lorentz force equation in order to Lorentz force equation in order to determine diffusion coefficientsdetermine diffusion coefficients

(Wommer et al. 2008)

Proton DistributionProton Distribution

(Wommer et al. 2008)

Simulated Gamma-ray Simulated Gamma-ray intensity mapintensity map

Intensity assuming Sagittarius A* as source of relativistic protons, B ~ 10μG

(Wommer et al. 2008)

Simulated Gamma-ray Simulated Gamma-ray intensity mapintensity map

Intensity assuming Sagittarius A* as source of relativistic protons matched to intensity range of HESS

(Wommer et al. 2008)

Simulated Gamma-ray energy Simulated Gamma-ray energy mapmap

Diffuse emission from Sagittarius A* in Diffuse emission from Sagittarius A* in simulation extends only a fraction of a simulation extends only a fraction of a degreedegree

Diffusion from galactic center is too slow to Diffusion from galactic center is too slow to account for emission beyond a fraction of account for emission beyond a fraction of a degreea degree

Morphology is inconsistent with HESS Morphology is inconsistent with HESS datadata

(Wommer et al. 2008)

Simulated Gamma-ray intensity Simulated Gamma-ray intensity map – multiple injection sitesmap – multiple injection sites

Intensity assuming 5 distinct sources of protons (from HESS observations), B = 10μG, intensity range of HESS

(Wommer et al. 2008)

Simulated Gamma-ray intensity Simulated Gamma-ray intensity map – multiple injection sitesmap – multiple injection sites

Intensity assuming 5 distinct sources of protons (from HESS observations), B = 100μG, intensity range of HESS

(Wommer et al. 2008)

Simulated Gamma-ray emission Simulated Gamma-ray emission map – multiple injection sitesmap – multiple injection sites

Emission is concentrated at the injection Emission is concentrated at the injection sitessites

Morphology is centrally peaked and Morphology is centrally peaked and inconsistent with HESS datainconsistent with HESS data

(Wommer et al. 2008)

Simulated Gamma-ray Simulated Gamma-ray intensity mapintensity map

Protons injected throughout the inter-cloud medium accelerated through second-order Fermi acceleration, B ~ 10μG, intensity range of HESS

(Wommer et al. 2008)

Simulated Gamma-ray intensity Simulated Gamma-ray intensity map – protons accelerated map – protons accelerated

throughout inter-cloud mediumthroughout inter-cloud medium Protons accelerated throughout the inter-Protons accelerated throughout the inter-

cloud medium by second-order Fermi cloud medium by second-order Fermi acceleration can produce a diffuse acceleration can produce a diffuse emission consistent with the HESS dataemission consistent with the HESS data

(Wommer et al. 2008)