Gazing into the heart of the Milky Way

Christi Cloete -- Mon, 08/04/2014 - 00:00

NWU: HESS picks up first pulsar signal

For the first time in its 12-year existence, the HESS observatory in Namibia has detected activity from a pulsar – a rapidly rotating, highly magnetised neutron star. This is only the second pulsar that has been spotted by a ground-based gamma-ray telescope anywhere in the world.

HESS stands for High Energy Stereoscopic System and is an international collaboration involving more than 170 scientists from 12 countries. The North-West University (NWU), which hosts the National Research Foundation’s (NRF) SARChi Chair of Astrophysics and Space Physics, has been part of the observation team since HESS was established in 2002.

Over the years, astrophysicists at the observatory have detected many exciting gamma-ray events, the latest being the pulsar signal detected in July 2014.

In this case, the HESS system measured pulsed radiation in the southern sky for the first time. The radiation originates from the Vela pulsar, the first pulsar detected by HESS and – after the Crab pulsar in 2011 – the second pulsar ever detected by ground-based gamma-ray telescopes.

The latest discovery follows the recent upgrade of the HESS observatory. Previously, it consisted of four Cherenkov telescopes and in 2012, a fifth and larger reflecting telescope of 28 metres was added, giving rise to what is known as HESS II.

The fifth telescope placed in the centre of the system extends the energy range to lower energies. This opens the door to new observation possibilities of the inner Galaxy.

The data reveals regular gamma-ray pulses at a frequency of 89 milliseconds, coming exactly from the direction of the Vela pulsar. According to preliminary analyses, everything suggests that these are gamma rays in the energy range of 30 GeV. This shows that HESS has for the first time successfully measured pulsed radiation in the southern sky, says Prof Markus Böttcher from the NWU.

Cherenkov telescope systems consist of optical telescopes which detect Cherenkov light flashes in the atmosphere. These flashes last only a few nanoseconds and are invisible to the human eye. They are generated by cascades of elementary particles triggered by cosmic radiation.

With highly sensitive cameras, Cherenkov telescopes take pictures of events, allowing for images to be constructed of cosmic particle accelerators which emit gamma radiation.

HESS is the only system of its kind in the southern hemisphere and the only one with different reflector sizes. Therefore, it ideally paves the way for the Cherenkov Telescope Array CTA, the next phase of international collaboration.

As from 2017, the CTA will be built with about 100 reflecting telescopes of three sizes, distributed over two sites, one of them possibly being in southern Namibia.

Gazing into the heart of the Milky Way

The whole Milky Way is full of pulsars and from Namibia you can see exactly into its centre.

The HESS data shows that, with Cherenkov telescopes, a number of mysteries can still be discovered in the universe. For example, data from the gamma-ray satellite, Fermi LAT, indicates that there is a mysterious gamma-ray source in the centre of the Galaxy. Scientists are already working on the first analysis of the corresponding data delivered by the new HESS system.