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LST receives signals from the Crab Pulsar

Following its inauguration in October 2018, the first LST (Large-Sized Telescope) is currently in the commissioning phase. The LST-1 will commence research operations in 2021. But the imposing gamma-ray telescope has already provided an important proof of its performance: It recorded the extremely weak signals of high-energy gamma radiation from a known source – the Crab Pulsar. The Max Planck Institute for Physics has made a substantial contribution to the design and construction of this telescope.

The LST-1 on the Canary Island of La Palma (Photo: Otger Ballester/IFAE)

The LST-1 on the Canary Island of La Palma (Photo: Otger Ballester/IFAE)

So far, there have been only four pulsars where telescopes have been able to detect very high-energy gamma emissions. The current measurements confirm hopes that scientists will be able to investigate the energy spectrum of further pulsars in detail.

The Crab Pulsar is the remnant of a supernova explosion in 1054. The neutron star has a diameter of only 20 kilometers, almost twice as heavy as the sun and rotates around its own axis about 30 times per second.

Like a lighthouse, it emits pulses of light – from long radio waves and visible light to short-wave, high-energy gamma rays. The pulsar is located in the center of the Crab Nebula. However, the nebula emits continuous gamma radiation that is 100 times more intense and therefore masks the weaker signals of the pulsar.

The recent data was recorded during 11.4 hours of observation during 10 nights in January and February 2020 and subsequently evaluated.

Optimized for weak gamma radiation

With a mirror diameter of 23 meters and a total height of 45 meters, the LST is the largest telescope in the Cherenkov Telescope Array (CTA). Despite its considerable size and weight of 100 tons, the LST can be steered to new sky positions in only 20 seconds.

Telescopes of this type are aimed at short, low-energy gamma rays in the energy range from 20 to 150 gigaelectronvolt. The scientists primarily use it to observe transient gamma radiation in our Milky Way as well as active galactic nuclei and distant gamma-ray bursts.

LST-1 is the first large telescope constructed as part of the CTA project. Four LST will be constructed on the Canary island of La Palma and four in Chile. With a number of small and medium-sized telescopes also planned for the CTA observatory, researchers will also be able to record higher energy ranges.

The LST-1 is currently being subjected to various tests. Before the LST-1 can be certified as a telescope in the multinational CTA Observatory (CTAO), it must – like all future telescopes and technical instruments – pass a critical examination. These measures are intended to ensure that its design is suitable for meeting the scientific goals, operational requirements, and safety standards of CTA.