Newly Found Supernova Remnants Revealed by Highest Gamma-Ray Energies

Over 200 sources of TeV radiation are known to date, both Galactic and Extragalactic. “We can often relate the radiation to known astrophysical objects that have been studied before with conventional telescopes in lower frequency bands, e.g. in optical or radio wavebands”, says Gerd Pühlhofer. 

But the H.E.S.S. telescopes delivered data that are detailed enough that the scientists could get further. “For the first time, we are now able to classify unidentified TeV sources to be members of a particular object class, using only the TeV data”, says Pühlhofer. “Three particular sources are now classified with high probability as supernova remnants.”

A supernova remnant is a celestial object that forms after the explosion of a massive star at the end of its lifetime. The matter that is expelled in such an explosion leads to shock waves that propagate into the interstellar medium. There, the matter is heated and particles are accelerated to relativistic speeds. The particles interact with light and gas in the neighbourhood of the sources and thus produce very high energy gamma rays. 

The question remains, states Gerd Pühlhofer, why these supernova remnants have escaped detection so far. “They are as large as the full moon, but totally invisible to the eye or to conventional, e.g. optical, telescopes”, explains the astrophysicist. He considers it possible that in previous sky surveys, because of their position in the Milky Way and because of their large extension, they were indistinguishable from the many other objects or they are partially covered by foreground gas. 

The community of gamma-ray astronomers is currently preparing the much more sensitive next-generation instrument for TeV gamma-ray astronomy, the Cherenkov Telescope Array CTA. Scheduled to move into regular operations in the 2020’s, it will provide a much more detailed and sensitive image of our Milky Way in gamma-rays.

Citation: A search for new supernova remnant shells in the Galactic plane with H.E.S.S.
Corresponding authors: G. Pühlhofer, D. Gottschall, M. Capasso.
H. Abdallah et al. (H.E.S.S. collaboration), Astronomy & Astrophysics, Vol. 612,
https://doi.org/10.1051/0004-6361/201730737

A&A special issue:https://www.aanda.org/component/toc/?task=topic&id=915