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تسجيل مستخدم جديدVHE gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S
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Supernova remnants (SNRs) are widely considered to be accelerators of cosmic rays (CR). They are also expected to produce very-high-energy (VHE; $E > 100$ GeV) gamma rays through interactions of high-energy particles with the surrounding medium and photon fields. They are, therefore, promising targets for observations with ground-based imaging atmospheric Cherenkov telescopes like the H.E.S.S. telescope array. VHE gamma-ray emission has already been discovered from a number of SNRs, establishing them as a prominent source class in the VHE domain. Of particular interest are the handful of SNRs whose X-ray spectra are dominated by non-thermal synchrotron emission, such as the VHE gamma-ray emitters RX J0852.0-4622 (Vela Jr.) and RX J1713-3946. The shell-type SNRs G1.9+0.3 and G330.2+1.0 also belong to this subclass and are further notable for their young ages ($leq 1$ kyr), especially G1.9+0.3, which was recently determined to be the youngest SNR in the Galaxy ($sim100$ yr). These unique characteristics motivated investigations with H.E.S.S. to search for VHE gamma rays. The results of the H.E.S.S. observations and analyses are presented, along with implications for potential particle acceleration scenarios.
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The non-thermal nature of the X-ray emission from the shell-type supernova remnants (SNRs) G1.9+0.3 and G330.2+1.0 is an indication of intense particle acceleration in the shock fronts of both objects. This suggests that the SNRs are prime candidates
for very-high-energy (VHE; E $>$ 0.1 TeV) {gamma}-ray observations. G1.9+0.3, recently established as the youngest known SNR in the Galaxy, also offers a unique opportunity to study the earliest stages of SNR evolution in the VHE domain. The purpose of this work is to probe the level of VHE {gamma}-ray emission from both SNRs and use this to constrain their physical properties. Observations were conducted with the H.E.S.S. (High Energy Stereoscopic System) Cherenkov telescope array over a more than six-year period spanning 2004-2010. The obtained data have effective livetimes of 67 h for G1.9+0.3 and 16 h for G330.2+1.0. The data are analyzed in the context of the multi-wavelength observations currently available and in the framework of both leptonic and hadronic particle acceleration scenarios. No significant {gamma}-ray signal from G1.9+0.3 or G330.2+1.0 was detected. Upper limits (99% confidence level) to the TeV flux from G1.9+0.3 and G330.2+1.0 for the assumed spectral index {Gamma} = 2.5 were set at 5.6 $times$ 10$^{-13}$ cm$^{-2}$ s$^{-1}$ above 0.26 TeV and 3.2 $times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ above 0.38 TeV, respectively. In a one-zone leptonic scenario, these upper limits imply lower limits on the interior magnetic field to B$_{mathrm{G1.9}}$ $gtrsim$ 11 {mu}G for G1.9+0.3 and to B$_{mathrm{G330}}$ $gtrsim$ 8 {mu}G for G330.2+1.0. In a hadronic scenario, the low ambient densities and the large distances to the SNRs result in very low predicted fluxes, for which the H.E.S.S. upper limits are not constraining.
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