High Energy emission from the Galactic Center Jason Ybarra

The Galactic Center Contains a supermassive black hole M = 3.6 × 106 M 3 main radio sources Sgr B, SgR C, SgR A Very dense molecular clouds Supernova remnants

Observations INTEGRAL IBIS/ISGRI (20-400 keV) HESS (0.1-20 TeV)

INTEGRAL observations IBIS/ISGRI imager 4.6 Ms total exposure time for observations between 2003-2004 Range 20-400 keV (Bélanger et al 2006)

INTEGRAL IBIS/ISGRI mosaic of GC in in the 20–40 keV range. (Bélanger et al 2006)

INTEGRAL 20-30 keV 30-40 keV 56-85 keV 40-56 keV (Bélanger et al 2006)

Spectrum of IGR 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 J17456−2901 1-10 keV from XMM-Newton. 20-400 keV from ISGRI Power law Γ2=3.22 Spectrum High-temp plasma (6.6 keV) Low temp plasma (1 keV) 6.4 keV Fe line Power law Γ=1.51 (Bélanger et al 2006)

Spectrum of IGR J17456−2901 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? X-Ray Transients Sgr A* flares Charged-Particle Acceleration

X-Ray Transients Large number of X-Ray transients near Sgr A* INTEGRAL Large number of X-Ray transients near Sgr A* 4 within 30″ of Sgr A* Light curves were constructed from Chandra and XMM-Newton data CXOGC J174535.5−290124 CXOGC J174540.0−290005 CXOGC J174540.0−290031 CXOGC J174538.0−290022 (Bélanger et al 2006)

X-Ray Transients Contemporaneous XMM-Newton data for J174540.0−290031 IGR J17456-2901 Contemporaneous XMM-Newton data for J174540.0−290031 Estimated flux ~ 5 x 1034 erg s-1 is still an order of magnitude too low. Spectrum of transient unlikely to be a pure power law > 100 keV CXOGC J174535.5−290124 CXOGC J174540.0−290005 CXOGC J174540.0−290031 CXOGC J174538.0−290022 (Bélanger et al 2006)

Possible Sources? X-Ray Transients Sgr A* flares Charged-Particle Acceleration Sgr A East

X-Ray Flares Flares occur on average once per day Average L ~ 1035 ergs s-1, but last for a few thousand seconds. The constant luminosity of IGR J17456-2901 cannot result from successive flares (Bélanger et al 2006)

Possible Sources? X-Ray Transients Sgr A* flares Charged-Particle Acceleration

Charged Particle Acceleration Perhaps same origin as the HESS TeV source The TeV emission is thought to come from the acceleration of particles (protons) to very high energies (Bélanger et al 2006)

Proton-Proton Collisions Accelerated protons are thought to collide with ambient protons p p

Proton-Proton Collisions Accelerated protons are thought to collide with ambient protons This interaction produces neutral pions p p p π0 p

Proton-Proton Collisions Neutral pions decay very quickly into two gamma rays p p p γ π0 γ p

Proton-Proton Collisions π+ p

Proton-Proton Collisions μ+ π+ νμ p

Proton-Proton Collisions Secondary electrons and positrons can produce gamma-rays through bremsstrahlung or inverse Compton scattering p p νe e+ n μ+ νμ π+ νμ p

Diffuse Emission Belanger et al. (2006) argue that the emission is diffuse Absence of variability Not detected by JEM-X (3′ resolution)

HESS High Energy Stereoscopic System (HESS) This is an array of 4 atmospheric Cherenkov Telescopes

HESS High Energy Stereoscopic System (HESS) This is an array of 4 atmospheric Cherenkov Telescopes

SNR/Pulsar Wind Nebula Galactic center HESS detected a point-like source of very-high energy gamma rays a the galactic center (HESS J1745-290). (Aharonian et al 2006)

The white contours indicate molecular gas traced by CS emission SNR/Pulsar Wind Nebula Galactic center The white contours indicate molecular gas traced by CS emission The correlation between molecular material and the faint γ-ray emission indicates cosmic ray origin (Aharonian et al 2006)

(Aharonian et al 2006)

Energy distribution The diffuse material exhibits the same power law index as HESS J1745-290 This suggests that J1745-290 is the source of cosmic rays that slowly diffuse out (Aharonian et al 2006)

What can accelerate the particles? Two possibilities: Supernova Remnant Sgr A East SMBH Sgr A*

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

Inverse Compton scattering Average energy lost by the photon ΔEγ/Eγ = - Eγ / mec2 Average energy gained by the photon ΔEγ/Eγ = 4/3 β2 γ2 ΔEγ/Eγ = 4/3 β2 γ2 - Eγ / mec2

Inverse Compton Scattering (Hinton & Aharonian 2007)

Inverse Compton Scattering The magnetic field strength is fixed at 105 μG (Hinton & Aharonian 2007)

Inverse 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 Annihilation Green - Minimal Supersymmetric Standard Model annihilation of 14 TeV neutralinos

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

Summary Inverse Compton scattering Two leading theories Gamma rays from accelerated particle interactions (p-p → p + p + π0, π0 → 2γ ) Inverse Compton scattering

References Aharonian et al (HESS Collaboration) 2006, PRL, 97, 221102 Belanger et al 2006, ApJ, 636, 275 Hinton, J. A. & Aharonian F. A. 2007, ApJ, 657, 302

Diffuse TeV Emission from the Galactic Center Jason Ybarra High Energy Astrophysics Seminar April 30, 2008

Previously … SNR/Pulsar Wind Nebula Galactic center HESS detected a point-like source of very-high energy gamma rays at the galactic center (HESS J1745-290). (Aharonian et al 2006)

The white contours indicate molecular gas traced by CS emission SNR/Pulsar Wind Nebula Galactic center The white contours indicate molecular gas traced by CS emission The correlation between molecular material and the faint γ-ray emission indicates cosmic ray origin (Aharonian et al 2006)

Energy distribution The diffuse material exhibits the same power law index as HESS J1745-290 This suggests that J1745-290 is the source of cosmic rays that slowly diffuse out (Aharonian et al 2006)

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

Simulations Distribution of molecular clouds Magnetic field modeled with Kolmogrov turbulence Wommer et al. 2008 (arXiv:0804.3111v1 [astro-ph] 18 Apr 2008)

Energy loss rates p-p scattering p-γ scattering Synchrotron cooling Compton scattering (Wommer et al. 2008)

Energy loss rates p-p scattering Compton scattering Cooling rates within the clouds Synchrotron cooling (Wommer et al. 2008)

Energy loss rates p-p scattering Compton scattering Cooling rates between the clouds Synchrotron cooling (Wommer et al. 2008)

Proton propagation F = qv × B Diffusion equation 1,000 protons were followed with the Lorentz force equation in order to determine diffusion coefficients (Wommer et al. 2008)

Proton Distribution (Wommer et al. 2008)

Simulated Gamma-ray intensity map Intensity assuming Sagittarius A* as source of relativistic protons, B ~ 10μG (Wommer et al. 2008)

Simulated Gamma-ray intensity map Intensity assuming Sagittarius A* as source of relativistic protons matched to intensity range of HESS (Wommer et al. 2008)

Simulated Gamma-ray energy map Diffuse emission from Sagittarius A* in simulation extends only a fraction of a degree Diffusion from galactic center is too slow to account for emission beyond a fraction of a degree Morphology is inconsistent with HESS data (Wommer et al. 2008)

Simulated Gamma-ray intensity map – 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 map – 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 map – multiple injection sites Emission is concentrated at the injection sites Morphology is centrally peaked and inconsistent with HESS data (Wommer et al. 2008)

Simulated Gamma-ray intensity 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 map – protons accelerated throughout inter-cloud medium Protons accelerated throughout the inter-cloud medium by second-order Fermi acceleration can produce a diffuse emission consistent with the HESS data (Wommer et al. 2008)