A breakthrough in the understanding of rare gamma rays caused by lightning

A breakthrough in the understanding of rare gamma rays caused by lightning

The telescopic array of detectors is deployed in the western desert of Utah. 507 detectors are located on a grid with an area of ​​700 km2

In the western desert of Utah, an array of telescopes on the territory occupied covers the parameters of New York. They were installed there in anticipation of cosmic radiation. The object captures high-energy particles that constantly collide with the earth's atmosphere. Cosmic rays activate 500-plus sensors every few minutes.

When checking data in 2013, physicists noticed a strange particle signature. It was the photon equivalent of light rain. In the array unexpectedly recorded a rare phenomenon - gamma rays. These are light waves of the highest energy in the EM spectrum arising from lightning strikes. After 5 years, a team from the University of Utah monitored descending ground gamma-ray flashes (TGF) in more detail.

The telescopic array captured 10 TGF bursts in the period 2014-2016. The project “Lightning Project” was the first to detect TGF at the beginning of a cloudy lightning and show where they appeared inside a thunderstorm. The telescopic array is now the only means of documenting the full TGF imprint and showing that gamma rays in diameter cover an area of ​​3-5 km.

Random Lab

The work is based on a study published last year. It established a strong correlation between similar bursts of energy particles detected in 2008–2013, as well as lightning activity registered by the national lightning detection network. Physicists were shocked.

For example, you can catch 4-5 detector activations within a millisecond. It is much faster than expected from cosmic rays. As a result, it became clear that all these strange events occurred under conditions of bad weather. In order to study lightning in more detail, researchers from the Langmuir Laboratory of Atmospheric Research were attracted. They installed a map of 9 stations that creates 3D images of radio frequency radiation. In 2014, an additional device was installed in the center of the array (“slow antenna”), which records changes in the electrical charge of a storm caused by a lightning strike.

Detection of the telescopic array and observation of lightning represent a new step in the understanding of TGF. Measurements also show that gamma rays are generated in short pulses, each of which only lasts from ten to several tens of microseconds.

Very rare phenomenon

The first TGF in 1994 recorded the Fermi satellite. Until then, physicists believed that only powerful celestial events, like the stellar explosion, were capable of creating gamma rays. Gradually, it became clear that the rays formed in the first milliseconds of ascending lightning.

Previously, only 6 TGFs were registered, two of which were created artificially in induced experiments. The remaining 4 studies with natural lightning reported that TGF arose much later when lightning struck the surface. Array observations are the first to show that TGFs occur at the initial stage of lightning destruction, similar to satellite observations.

What's next?

A lot of questions remained unanswered. For example, not all lightning strikes create flares. The thing is that there is only one specific type? The team hopes to install additional sensors in the array to improve the lightning measurement process.

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