Pancake stacks of radiation-sensitive film capture most accurate image of star’s gamma-ray beam

A stack of radioactive-sensitive films carried through the sky by a balloon was able to take the world’s most accurate pictures of the gamma-ray beam of a neutron star. To achieve this, researchers at Kobe University combined the oldest methods of capturing radioactive radiation with the latest data capture technology and ingenious time recording devices.

Stars emit light to us in various spectral ranges, from infrared to gamma rays. For each frequency band, different sensing equipment is required. The most challenging are gamma rays, known as the high-energy products of nuclear fission, because their very short wavelength means they do not interact with matter like other forms of light and therefore cannot be deflected through a lens or Detected via standard sensors. As a result, there is a gap in our ability to detect light from fascinating stellar objects such as supernovae and their remnants.

To solve this problem, Kobe University astrophysicist Shigeki Aoki and his team turned to the first material used to detect radioactivity, film.

“Our team has been focusing on the latex film’s remarkable ability to track gamma rays with high precision and proposed that it could become an excellent gamma-ray telescope by introducing a variety of modern data capture and analysis capabilities,” Aoki explained.

Based on the high sensitivity of these films and the novel, automated, high-speed process of extracting data from them, the idea is to stack some of these films to accurately capture the trajectories of particles produced by gamma rays on top of them. Just like a pancake you can capture where you stick a straw in it, but it takes a whole stack of pancakes to record the direction of the straw.

In order to reduce atmospheric interference, they installed the stack of film on a scientific observation balloon and raised it to an altitude of 35 to 40 kilometers. However, because the balloon swayed and twisted in the wind, the direction of the “telescope” was unstable, so they added a set of cameras to record the gondola’s position relative to the stars at any time. But this creates another problem, because as anyone who has ever taken a long-exposure photo knows, film does not record the passage of time, so there is no direct way to know when any given gamma-ray hit occurred.

To overcome this problem, they made the bottom three membranes move back and forth at regular but different speeds, like the hands of a clock. Based on the relative misalignment of the marks in these lower plates, they were able to calculate the precise time of impact, correlating it with the camera footage.

They have now published the first image produced by this setup in the journal The Astrophysical Journal. This is the most accurate image ever produced of the Vela pulsar, a rapidly spinning neutron star that projects a beam of gamma rays into the sky like a beacon at night.

“In total, we captured trillions of trajectories with an accuracy of 1/10,000 mm. By adding time information and combining it with attitude monitoring information, we were able to pinpoint the ‘when’ and ‘where’ of the event. From this The resulting resolution is more than 40 times higher than conventional gamma-ray telescopes,” Aoki summed up his team’s achievement.

While these results are already impressive, new technology opens up the possibility of capturing more detail than ever before in this optical frequency band.

Researchers from Kobe University explain: “Through scientific balloon-borne experiments, we can try to contribute to many fields of astrophysics, in particular opening up gamma-ray telescopes for ‘multi-messenger astronomy’, in which the same Objects require different techniques to capture events. Based on the success of the 2018 balloon experiment in generating these data, we will expand the observation area and time in future balloon flights, and look forward to scientific breakthroughs in the field of gamma-ray astronomy.”