Download Diffuse TeV Emission from the Galactic Center

High Energy emission
from the Galactic Center
Jason Ybarra
The Galactic Center
Contains a supermassive black hole
M = 3.6 × 106 M
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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)
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INTEGRAL observations
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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)
Power law Γ=1.51
Low temp
plasma (1 keV)
6.4 keV Fe line
(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?
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X-Ray Transients
Sgr A* flares
Charged-Particle Acceleration
X-Ray Transients
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Large number of X-Ray
transients near Sgr A*
4 within 30″ of Sgr A*
Light curves were
constructed from
Chandra and XMMNewton data
INTEGRAL
CXOGC J174535.5−290124
CXOGC J174540.0−290005
CXOGC J174540.0−290031
CXOGC J174538.0−290022
(Bélanger et al 2006)
X-Ray Transients
IGR J17456-2901
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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?
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X-Ray Transients
Sgr A* flares
Charged-Particle Acceleration
Sgr A East
X-Ray Flares
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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?
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X-Ray Transients
Sgr A* flares
Charged-Particle Acceleration
Charged Particle Acceleration
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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
p
Neutral pions decay very quickly
into two gamma rays
p
p
γ
π0
p
γ
Proton-Proton Collisions
p
p
n
π+
p
Proton-Proton Collisions
p
p
n
μ+
π+
p
νμ
Proton-Proton Collisions
Secondary electrons and positrons can
produce gamma-rays through
bremsstrahlung or inverse Compton
scattering
p
νe
p
e+
n
μ+
π+
p
νμ
νμ
Diffuse Emission
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1)
2)
Belanger et al. (2006) argue that the emission is
diffuse
Absence of variability
Not detected by JEM-X (3′ resolution)
HESS
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High Energy Stereoscopic System (HESS)
This is an array of 4 atmospheric Cherenkov
Telescopes
HESS
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High Energy Stereoscopic System (HESS)
This is an array of 4 atmospheric Cherenkov
Telescopes
SNR/Pulsar Wind
Nebula
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Galactic center
HESS detected a pointlike source of very-high
energy gamma rays a the
galactic center (HESS
J1745-290).
(Aharonian et al 2006)
SNR/Pulsar Wind
Nebula
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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
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The diffuse material
exhibits the same power
law index as HESS
J1745-290
This suggests that J1745290 is the source of
cosmic rays that slowly
diffuse out
(Aharonian et al 2006)
What can accelerate the particles?
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1)
2)
Two possibilities:
Supernova Remnant Sgr A East
SMBH Sgr A*
Inverse Compton scattering
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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
1.
Two leading theories
Gamma rays from accelerated particle
interactions (p-p → p + p + π0, π0 → 2γ )
2.
Inverse Compton scattering
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References
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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 …
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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)
SNR/Pulsar Wind
Nebula
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
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
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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* account for the diffuse emission seen
by HESS?
Simulations
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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
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p-p scattering
p-γ scattering
Synchrotron cooling
Compton scattering
(Wommer et al. 2008)
Energy loss rates
p-p scattering
Compton scattering
Synchrotron cooling
Cooling rates within the
clouds
(Wommer et al. 2008)
Energy loss rates
p-p scattering
Compton scattering
Synchrotron cooling
Cooling rates between the
clouds
(Wommer et al. 2008)
Proton propagation
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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
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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
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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
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Protons accelerated throughout the intercloud medium by second-order Fermi
acceleration can produce a diffuse
emission consistent with the HESS data
(Wommer et al. 2008)