Astronomers have measured very-high-energy gamma rays coming from the aftermath of a gamma ray burst – an enormously energetic explosion of a star in another galaxy. The results shine light on these immensely powerful but little-understood cosmic events, and challenge standard models of how gamma ray bursts radiate light during their afterglow phases. As a dying massive star enters its final death throes, its core begins to collapse, and then explodes as a supernova. Some types of supernovae generate jets of particles moving at close to the speed of light; if the jet is pointed directly towards Earth it can be observed as a burst of gamma ray radiation that lasts several seconds. These gamma ray bursts are sometimes followed by a weaker afterglow lasting hours or days, created as the particle jet slams into surrounding gas.
The H.E.S.S. Collaboration used the High Energy Stereoscopic System (H.E.S.S) – an array of five gamma-ray telescopes located in Namibia – to observe the afterglow of the gamma ray burst GRB 190829A on three consecutive nights. The authors detected emission at energies of several tera-electronvolts from 4.3 hours to 55.9 hours after the gamma ray burst began, and determined the intrinsic high-energy spectrum. These emissions had similar spectral properties and decay profiles to the x-ray emission coming from GRB 190829A. The researchers argue that this spectral behavior doesn’t match current emission models for gamma ray burst afterglows, but speculate that a faster jet or different energy distributions of emitted particles could explain the discrepancy.
