Abstract
We present results from deep observations of the Galactic shell-type supernova remnant (SNR) RX J1713.7-3946 (also known as G347.3-0.5) conducted with the complete H.E.S.S. array in 2004. Detailed morphological and spatially resolved spectral studies reveal the very-high-energy (VHE -- Energies E > 100 GeV) gamma-ray aspects of this object with unprecedented precision. Since this is the first in-depth analysis of an extended VHE gamma-ray source, we present a thorough discussion of our methodology and investigations of possible sources of systematic errors. Gamma rays are detected throughout the whole SNR. The emission is found to resemble a shell structure with increased fluxes from the western and northwestern parts. The differential gamma-ray spectrum of the whole SNR is measured over more than two orders of magnitude, from 190 GeV to 40 TeV, and is rather hard with indications for a deviation from a pure power law at high energies. Spectra have also been determined for spatially separated regions of RX J1713.7-3946. The flux values vary by more than a factor of two, but no significant change in spectral shape is found. There is a striking correlation between the X-ray and the gamma-ray image. Radial profiles in both wavelength regimes reveal the same shape almost everywhere in the region of the SNR. The VHE gamma-ray emission of RX J1713.7-3946 is phenomenologically discussed for two scenarios, one where the gamma rays are produced by VHE electrons via Inverse Compton scattering and one where the gamma rays are due to neutral pion decay from proton-proton interactions. In conjunction with multi-wavelength considerations, the latter case is favoured. However, no decisive conclusions can yet be drawn regarding the parent particle population dominantly responsible for the gamma-ray emission from RX J1713.7-3946.
Highlights
It is commonly believed that the only sources capable of supplying enough energy output to power the flux of Galactic cosmic rays are supernova explosions (e.g., Ginzburg & Syrovatskii 1964)
With the High Energy Stereoscopic System (HESS) data set, the morphology of RX J1713.7−3946 and its spectrum are resolved with high precision
Given that this is the first in depth analysis of such an extended source in VHE gamma rays, we present in the following first selected examples of extensive systematic tests that were performed in order to assure the stability of the analysis and discuss the results
Summary
It is commonly believed that the only sources capable of supplying enough energy output to power the flux of Galactic cosmic rays are supernova explosions (e.g., Ginzburg & Syrovatskii 1964). At the present time there are two main arguments for this hypothesis: firstly, estimates of the power required to sustain the observed nuclear Galactic cosmic-ray population show that about 10% of the mechanical energy released by the population of Galactic supernovae would suffice, or, in other words, that supernova remnants could be the sources of the Galactic cosmic rays if the average acceleration efficiency in a remnant is about 10%. The best way of proving unequivocally the existence of very-high-energy (VHE) particles, electrons or hadrons, in the shells of supernova remnants (SNRs) is the detection of VHE (about 100 GeV up to a few tens of TeV) gamma rays produced either via Inverse Compton (IC) scattering of VHE electrons off ambient photons or in interactions of nucleonic cosmic rays with ambient matter. One should note that there exist two other experimental approaches to trace VHE cosmic rays, the detection of X-rays, which suggests the presence of VHE electrons (Koyama et al 1995), and of high-energy neutrinos, which probe exclusively nuclear particles
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