Acceleration of Electrons and Protons by Plasma Waves in Sgr A*
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Acceleration of Electrons and Protons by Plasma Waves in Sgr A*
Siming LiuPhysics Department, Stanford University
Vahé PetrosianDept. of Physics and Applied Physics, Stanford University
Fulvio MeliaDept. of Physics, University of Arizona
SLAC, GLAST, Aug. 25 2005
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Outline
Observations of Sgr A*Evidence for Electron Acceleration
A: radio emissionB: NIR and X-ray flares.
Evidence for Proton Acceleration
Stochastic Acceleration by Plasma Waves
Structure of the Accretion Flow in Sgr A*
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Broadband Spectrum
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Zhao et al. 1991, Nature, 354, 46
2 cm radio image of the central two light year region (~20”).
VLA
Lo et al. 1998, ApJ, 508, 61
Bower et al. 2004, Science, 304, 704
Shödel, R. et al. 2002, Nature
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Evidence for Energetic Electrons
Liu and Melia 2001, ApJ, 561, 77
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Evidence for Energetic Electrons
Liu et al. 2005, ApJ
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HESS
H.E.S.S. Preliminary
HESS Collaboration 2004
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Possible ExplanationsSynchrotron Self-Comptonination
Atoyan and Dermer 2004, ApJ, 617, 123
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Possible ExplanationsPhoto-Meson Interactions
Aharonian et al 2005, ApJ, 619, 306
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Possible ExplanationsProton-Proton Interactions
Aharonian et al 2005, ApJ, 619, 306; Liu et al. 2005
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Acceleration within 20rS
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Stochastic Particle Acceleration
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Stochastic Particle Acceleration
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Stochastic Particle Acceleration
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Proton Acceleration
Cooling is too efficientto produce 7mm emission
Source is too bright in the radioband.
Source is optically thin at 7mm
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The HESS source is likely produced via pp scatterings by protons
accelerated near the black hole and diffusing toward large radii.
Should the 7mm emission be produced by electrons in the
acceleration region, the acceleration region must be strongly magnetized.
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Structure of the Accretion Flow
De Villiers et al. 2003 ApJ
Sub-mm, NIR, and X-ray via Synchrotron and SSC
cm and mm via Synchrotron and proton acceleration
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Conclusions
In combination with the theory of Stochastic Acceleration by
plasma waves and MHD simulations, observations over a broad energy range can be used to detect the properties
of accretion flows
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Emission Spectra
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Emission Processes During FlaresThermal Synchrotron and SSC:
Four ParametersB, kBT = γcrmec2, N , A≈R2
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(From Zhao et al.
2004)(From Bower, Falcke et al.
2004)
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NIR Flares From Sgr A*Quasi-periodic Modulation
Genzel et al. 2003
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X-Ray Flares From Sgr A*Quasi-periodic Modulation
Belanger et al. 2005
Baganoff et al. 2001 Porquet et al. 2003
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Lx ~ 6x1033 erg s-1
Lnir ~ 5x1034 erg s-1
Eckart et al. (2004)
Sgr A* 19-20 June 2003 – NIR/X-ray Flare
Baganoff 2005
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Emission Processes During Flares
Thermal Synchrotron
and SSC:Four
ParametersN=3.8x1042
kBT=75mec2
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Emission Spectra
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Emission Spectra
Soft NIR Flares
Hard X-ray Flares
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τrise
Constraining T & B with NIR and X-ray Spectra and flare rise time
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Stochastic Electron Acceleration
Maxiwellian
Continuousheating andcooling
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Determining the Plasma Properties
Observations
B, R, n, fturb
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Stochastic Electron Acceleration
Maxiwellian
Without injection:Continuousheating andcooling
InjectionContinuousinjection, heating, &cooling.
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HESS Source
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scan: 07:06:22:35:11.8 - 07:07:12:53:44.9
flare: 07:07:03:12:20.0 - 07:07:03:54:12.8
July 2004: Detection of a Strong X-ray flare
18x
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Comparison of X-ray and NIR Lightcurves •At least four separate NIR
flares were detected at K-band by the VLT with NAOS/CONICA on 2004 July 6/7.
•NIR flare III is correlated with the strong X-ray flare.
•NIR flare I is associated with the possible X-ray event at the beginning of the observations, but the ratio of X-ray to NIR amplitudes is clearly different.
•Additional strong NIR flares (II and IV) have no detected X-ray counterparts.
Baganoff 2005
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X-ray image of Sgr A*
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X-ray Flares from Sgr A*(Baganoff et al. 2001)
In flare-state, Sgr A*’s X-ray luminosity can increase by more than one order of magnitude.
The X-ray flare lasted for a few hours. Significant variation in flux was seen over a 10 minute interval.
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