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Register a new userA dense gas survey of the gamma-ray sources HESS J1731-347 and HESS J1729-345
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The results of Mopra molecular spectral line observations towards the supernova remnant HESSJ1731-347 (G353.6-0.7) and the unidentified gamma-ray source HESSJ1729-345 are presented. Dense molecular gas in three different velocity-bands (corresponding to three Galactic arms) are investigated using the CS(1-0) line. The CS-traced component provides information about the dense target material in a hadronic scenario for gamma-ray production (cosmic rays interacting with gas) and an understanding of the dynamics. Furthermore, the effects of cosmic ray diffusion into dense gas may alter the gamma-ray spectrum to cause a flattening of spectra towards such regions. Dense molecular gas mass at a level of ~10^5 Mo was revealed in this survey, with mass of the order of ~10^3 Mo towards HESSJ1729-345 in each coincident Galactic arm, but no significant detection of dense molecular gas towards HESSJ1731-347 at the currently-preferred distance of ~5.2-6.2 kpc was discovered.
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In the survey of the Galactic plane conducted with H.E.S.S., many VHE gamma-ray sources were discovered for which no clear counterpart at other wavelengths could be identified. HESS J1731-347 initially belonged to this source class. Recently however, the new shell-type supernova remnant (SNR) G353.6-0.7 was discovered in radio data, positionally coinciding with the VHE source. We will present new X-ray observations that cover a fraction of the VHE source, revealing nonthermal emission that most likely can be interpreted as synchrotron emission from high-energy electrons. This, along with a larger H.E.S.S. data set which comprises more than twice the observation time used in the discovery paper, allows us to test whether the VHE source may indeed be attributed to shell-type emission from that new SNR. If true, this would make HESS J1731-347 a new object in the small but growing class of non-thermal shell-type supernova remnants with VHE emission.
We report the detection of GeV $gamma$-ray emission from supernova remnant HESS J1731-347 using 9 years of {it Fermi} Large Area Telescope data. We find a slightly extended GeV source in the direction of HESS J1731-347. The spectrum above 1 GeV can be fitted by a power-law with an index of $Gamma = 1.77pm0.14$, and the GeV spectrum connects smoothly with the TeV spectrum of HESS J1731-347. Either a hadronic-leptonic or a pure leptonic model can fit the multi-wavelength spectral energy distribution of the source. However, the hard GeV $gamma$-ray spectrum is more naturally produced in a leptonic (inverse Compton scattering) scenario, under the framework of diffusive shock acceleration. We also searched for the GeV $gamma$-ray emission from the nearby TeV source HESS J1729-345. No significant GeV $gamma$-ray emission is found, and upper limits are derived.
The supernova remnant (SNR) HESS J1731-347 is a young SNR which displays a non-thermal X-ray and TeV shell structure. A molecular cloud at a distance of 3.2 kpc is spatially coincident with the western part of the SNR, and it is likely hit by the SNR. The X-ray emission from this part of the shell is much lower than from the rest of the SNR. Moreover, a compact GeV emission region coincident with the cloud has been detected with a soft spectrum. These observations seem to imply a shock-cloud collision scenario at this area, where the stalled shock can no longer accelerate super-TeV electrons or maintain strong magnetic turbulence downstream, while the GeV cosmic rays (CRs) are released through this stalled shock. To test this hypothesis, we have performed a detailed Fermi-LAT reanalysis of the HESS J1731-347 region with over 9 years of data. We find that the compact GeV emission region displays a spectral power-law index of -2.4, whereas the GeV emission from the rest of the SNR (excluding the cloud region) has an index of -1.8. A hadronic model involving a shock-cloud collision scenario is built to explain the -ray emission from this area. It consists of three CR sources: run-away super-TeV CRs that have escaped from the fast shock, leaked GeV CRs from the stalled shock, and the local CR sea. The X-ray and -ray emission of the SNR excluding the shock-cloud interaction region is explained in a one-zone leptonic model. Our shock-cloud collision model explains well the GeV-TeV observations from both cloud regions around HESS J1731-347, i.e. from the cloud in contact with the SNR and from the more distant cloud which is coincident with the nearby TeV source HESS J1729-345. We find however that the leaked GeV CRs from the shock-cloud collision do not necessarily dominate the GeV emission from the clouds, due to a comparable contribution from the local CR sea.
HESS J1731-347 is a shell-type supernova remnant emitting both TeV gamma rays and non-thermal X-ray photons, spatially coincident with the radio SNR G353.6-0.7. Hadronic and leptonic scenarios (or a blend of both) are discussed in the literature to explain the TeV emission from the object. In 2011, a $gamma$-ray excess was also found in the neighborhood of the source (HESS J1729-345). Here we present results of an updated analysis obtained with the meanwhile available additional H.E.S.S. data. Beyond HESS J1731-347, the analysis reveals the morphology of the emission of the adjacent TeV source HESS J1729-345 and the emission in between the two sources in greater detail. The results permit us to correlate the TeV emission outside of the SNR with molecular gas tracers, and to confront the data with scenarios in which the TeV emission outside the SNR is produced by escaping cosmic rays.
A detailed analysis of the nonthermal X-ray emission from the North-Western and Southern parts of the supernova remnant (SNR) HESS J1731$ - $347 with {it Suzaku} is presented. The shell portions covered by the observations emit hard and line-less X-rays. The spectrum can be reproduced by a simple absorbed power-law model with a photon index $Gamma$ of 1.8-2.7 and an absorption column density $N_{rm H}$ of (1.0-2.1)$times 10^{22}$ cm$^{-2}$. These quantities change significantly from region to region; the North-Western part of the SNR has the hardest and most absorbed spectrum. The Western part of the X-ray shell has a smaller curvature than North-Western and Southern shell segments. A comparison of the X-ray morphology to the Very High Energy (VHE) gamma-ray and radio images was performed. The efficiency of electron acceleration and emission mechanism in each portion of the shell are discussed. Thermal X-ray emission from the SNR was searched for but could not be detected at a significant level.
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