Scientists from China, Europe to target gamma-rays from Tiangong space station

The project’s technical manager Nicolas Produit, a physicist from the University of Geneva, said the telescope will be mounted on the Tiangong’s exterior to look for gamma-ray bursts (GRBs) – energetic light particles from the most powerful cosmic explosions since the Big Bang.

Speaking at the International Astronautical Congress in Baku, Azerbaijan, on Wednesday, Produit said Polar-2 is expected to detect around 200 GRBs every year, for at least two years.

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GRBs were first discovered more than five decades ago, but where they come from and how they are produced remain poorly understood, he noted.

One hypothesis is that they are launched from the centre of explosions caused by events such as the birth of a black hole or the collision of the dense, spinning cores of collapsed stars.

Scientists have observed that the bursts occur about once per day, with brief but intense flashes of gamma radiation. GRBs are challenging to detect because they happen at random locations and times in the universe.

In 2016, Produit was manager of Polar-2’s predecessor mission, a collaboration between researchers from Switzerland, China and Poland, that aimed to answer questions about the structure, magnetic field and emission mechanism of the bursts.

The team developed a GRB polarimeter that spent six months on board China’s Tiangong-2 space lab measuring the angle of rotation of light particles picked up by a gamma-ray detector.

The first Polar mission was considered highly successful, recording 55 bursts and obtaining high-precision measurements for five of them. But the results also showed the complex nature of GBRs and prompted the team to build a much bigger detector, Produit said.

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As a follow-up mission, Polar-2 will use similar technologies but is four times bigger and 10 times more sensitive than its predecessor, thanks to the development of silicon-based photomultiplier tubes, he said.

Polar-2 is one of seven international experiments, selected by the China Manned Space Agency (CMSA) and the United Nations Office for Outer Space Affairs in 2019, to be hosted by Tiangong.

Speaking at the same conference, Lyu Congmin, deputy chief designer of CMSA’s space utilisation system, said another project, developed by Chinese and Japanese researchers, had already arrived at Tiangong.

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The experiment, focusing on the study of flame instability and engine combustion in microgravity, would be rolled out soon, Lyu said. He also flagged that a second round call for international proposals on Tiangong could be expected soon.

A separate China-Europe mission dedicated to the study of GRBs – the space-based multi-band astronomical variable objects monitor, dubbed SVOM – is scheduled to leave the Xichang satellite launch centre atop a Long March 2C rocket early next year.