Study inspects gamma ray emission from HESS J1809−193

Study inspects gamma ray emission from HESS J1809−193

Map showing the 𝛾-ray flux above 0.27 TeV from HESS J1809−193. (a) full region. (b) zoom in on the central region. Credit: Mohrmann et al, 2023

Using the High Energy Stereoscopic System (HESS), German astronomers studied a very high energy (VHE) gamma ray source known as HESS J1809−193. The results of the study, published on January 18 on the arXiv preprint server, provide important information about the properties of gamma ray emission from this source.

Sources emitting gamma radiation with photon energies between 100 GeV and 100 TeV are called very high energy (THE) gamma ray sources, while those with photon energies greater than 0.1 PeV are called ultra-high energy (UHE) gamma ray sources. The nature of these sources is not yet fully understood; therefore, astronomers are constantly on the lookout for new such objects to characterize them, which could shed more light on their properties in general.

Discovered in 2007 as part of the HESS Galactic Plane Survey (HGPS), HESS J1809−193 is an unassociated HEV (over 100 GeV) gamma ray source. Previous observations of HESS J1809−193 have shown that the source is located in a rich environment, with an energetic pulsar (designated PSR J1809−1917) at a distance of about 10,750 Light yearspulsar X-ray wind nebula (PWN), several supernova remnants (SNR) and molecular clouds.

Recently, gamma ray emission up to energies of about 100 TeV was detected by HESS J1809−193 with the High Altitude Water Cherenkov Observatory (HAWC). The discovery means that this source may be able to accelerate cosmic rays down to PeV energies.

In order to verify this hypothesis, a team of astronomers led by Lars Mohrmann of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, carried out follow-up observations of HESS J1809−193 using the HESS network of telescopes. Cherenkov. Their study was supplemented with data from NASA’s Fermi spacecraft.

“We present a new analysis of the TeV gamma ray emission from HESS J1809−193 with HESS, based on improved analysis techniques…We used 93.2 h of data taken on HESS J1809−193 with the four 12m diameter telescopes For the high-level analysis, we used the Gammapy package and performed a spectro-morphological likelihood analysis which uses as input a background model constructed from archival HESS observations” , the researchers explained.

The team succeeded in resolving the emission of HESS J1809−193 into two components (A and B) which exhibit distinct spectra and morphologies. The spectral indices of components A and B were measured at a level of 2.24 and 1.98, respectively. However, the astronomers noted that the upper limits at high energies for the A component indicate that the spectrum may cut off before reaching 100 TeV.

According to the authors of the paper, the results suggest that the extended A component of HESS J1809−193 is consistent with a halo of old electrons surrounding a compact PWN. As for component B, they speculate that it could possibly be of lepton or hadronic origin.

The researchers added that the presence of supernova remnants and molecular clouds in the HESS J1809−193 region indicate that a hadronic scenario should be considered, in which part of the emission could be due to ray nuclei. cosmic particles accelerated by SNRs and interacting with the gas. in the clouds.

More information:
Lars Mohrmann et al, Revisiting HESS J1809–193—a very high-energy gamma-ray source in a fascinating environment, arXiv (2023). DOI: 10.48550/arxiv.2301.07366

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