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Gamma-rays from the GC

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M.Chernyakova (DIAS), D.Malyshev (DIAS), F.Aharonian (DIAS, MPIK), R.M.Crocker(MPIK), D.I.Jones(MPIK)

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10°x10° Count and TS maps (>300 GeV)

Gamma-rays from the GC
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TS maps of the GC at different energies
300 MeV ­ 3GeV 3 GeV ­ 30 GeV 30 GeV ­ 300 GeV

Gamma-rays from the GC
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Gamma-rays from the GC

Lightcurve


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Gamma-rays from the GC

Source spectrum


Model
X-ray and low-energy emission come from the central object, probably SMBH accretion disk. The same central object is a source of high-energy protons and electrons. As proposed in Aharonian & Neronov (2005), a significant fraction of the protons accelerated near the black hole may enter the surrounding gaseous environment and initiate VHE gamma-ray emission through neutral pion production and subsequent decay.

Gamma-rays from the GC
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Diffusion approximation
In the standard diffusion approximation the propagation of particles is described by the diffusion equation which, in the spherically symmetric case, reduces to the form:

Gamma-rays from the GC

continuous energy loss rate

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Formally, the diffusion equation does not contain information on how fast a particle may propagate. Since classical solution (Syrovatskii 1959) does not prevent an artificial "superluminal motion", we follow the phenomenological approach proposed by by Aloisio, Berezinsky & Gazizov (2009) to avoid this problem.


Proton spectrum
At high energies protons move with the speed of light and thus their number in the cloud remain constant At low energies due to diffusion protons are entangled and their number in the cloud grows with time The shape of the spectra is the same at low and high energies and similar to injected from central source. The photon spectra from pp collisions looks similar to proton spectra.

Gamma-rays from the GC
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Due to the energy dependence of the diffusion coefficient, proton propagation is quite different at low as compared to high energies


Proton radial distribution
Gamma-rays from the GC
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-ray spectra under different assumptions

Gamma-rays from the GC
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Flares
TeV protons in our model are quite young and left the source about
t~R/c~10(R/3pc)

Gamma-rays from the GC

years ago, while the GeV protons are much older.
Spectra of gamma-ray emission resulting from realization of three different scenarios: (i) a proton flare of 10 years duration that occurred 300 years ago, (ii) a constant source that switched on 104 years ago, and (iii) a proton flare on top of the constant source .

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-ray radial distribution
We can't study the details of gamma-rays spatial distribution, but radio emission resulted from synchrotron emission of the secondary electrons and positrons can give us an answer.

Gamma-rays from the GC
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Conclusions
We have analyzed 25 months of Fermi data on the GC region. The Fermi-LAT source 1FGL J1745.6-2900 lies within the error box of HESS source J1745-290. While below 5 GeV the spectrum of 1FGL J1745.6-2900 has a photon spectral index similar to the HESS source, the spectrum at higher energies is better described by a steeper spectral index Hadronic interactions of relativistic protons which, having diffused away from a central source, produces a photon spectrum that can naturally explain the observed broad-band gamma-ray emission. The available spectral information can be well described with different sets of model parameters and additional information is required to distinguish model scenarios. Such information can be obtained from the spatial distribution of the gamma-ray emission and radio emission resulted from synchrotron emission of the secondary electrons and positrons

Gamma-rays from the GC
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Diffusion approximation

Gamma-rays from the GC
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Diffusion approximation, phenomenological approach

Gamma-rays from the GC
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Gamma-rays from the GC