On December 20, 2022, this landmark article was accepted by ApJL—Astrophysical Bulletin—while staying at home and waiting for the sun.The signature significance is that the microwave radiation data of solar flares came from independent research equipment – the 35-40GHz millimeter-wave solar radio spectrometer – the world's first and only millimeter-wave radio spectrometer.
Development of the device began in early 2018 and lasted nearly five years until the first flare research article was published.The first version of the device was built more than two years ago and put into routine observation.However, the first two years of solar rest are in the middle of low activity, and there are few large flares.Over the course of the day, only one large X-class flare and one medium-strength M-class flare were caught, and the remaining relatively weak flares were mostly submerged in equipment noise (or no observable signal was generated at all).As a result, the biggest problem with the system was that it was too noisy or too sensitive: the solar disk as a whole was a strong source of millimeter-wave radiation, and flares—from a very small source—were often small.
In order to solve this critical problem, on the basis of the first edition, the team redesigned, tested and adjusted the equipment, added a special standard noise source for calibration, introduced a thermostatic device.This results in a second version, enabling the first iteration of the technology driven by problems or scientific research needs.
The event reported in this article is actually the first flare event observed by the first edition of the device.The intensity of the signal - comfortably much higher than the intensity of radiation in the same frequency band on the solar disk - is therefore significantly encouraging.
After the equipment is built, the analysis and processing of data, especially calibration, is also a big problem.The first version of the device does not use constant temperature control, and millimeter wave radiation is significantly affected by cloud, water vapor, and ambient temperature, so it is not easy to correct the system reading to the standard solar radiation flow unit.The research team tried to use the new moon calibration method, which observed the new moon rising with the sun on the 30th or early evening of each month, and calibrated the measurement value of solar eruption based on known crescent radiation intensity.In the second edition, standard noise sources were added—although this would result in new interpolation losses that would be properly tolerated—and the calibration accuracy was much higher than that of the first edition of Crescent Calibration.In the new version, the full-waveguide hard-touch connection method is used to achieve the purpose of reducing the system noise coefficient.
Therefore, in order to meet the needs of scientific research innovation, it is necessary to develop new research equipment in unmanned areas; and the equipment will generate new observation data, which is expected to make new discoveries.Approximately one or two rounds of such scientific-technical-equipment renewal iterations or cycles are expected to step into the so-called "leading" position in the field.The Laboratory for Electromagnetic Detection, known simply as LEAD, has this vision.This also shows us a "high-level science and technology self-reliance" of the "three new" path.
Well, let's get down to business and continue with the new features of the flares millimeter wave radiation studied in this article.First, the key scientific goal of the device is to accurately measure the flare millimeter wave cyclotron synchrotron radiation spectrum!This is crucial!Why? In flares, a lot of energy is first transferred to high-energy electrons, and then these high-energy electrons produce so-called flares from radiation such as microwave (including millimeter waves) radio and hard X-rays.
However, it is impossible to directly detect the high-energy electrons in the flares area, and the properties of the high-energy electrons can only be inferred by detecting the corresponding electromagnetic radiation.Microwave radiation is a good electromagnetic window for detecting flares and high-energy electrons.In the past, radiation flow could only be measured at a very small number of discrete frequencies such as 35 GHz at Yamadai Station in Nobe, Japan, so measurements of the flare millimeter wave radiation spectrum were unreliable or even impossible.The instrument developed this time, although it is only a small part of the microwave frequency domain, still plays a very good "demonstration" role, and has been effective in limiting the parameters of millimeter wave radiation spectrum!
Theoretically, our equipment can give radiation flow at tens of thousands of frequencies in the 35-40 GHz range.Of course, in order to determine the radiation spectrum, it is not necessary to have so many frequency points, about ten is enough.These frequencies, combined with the 17 and 35 GHz double-frequency data given by the above Japanese stations, can very well limit the spectral parameters of a considerable portion of the cyclotron synchrotron radiation spectrum, especially when the peak frequency is below 35 GHz.These conclusions are possible because of this new device and calibrated data.This type of high flip frequency event, mostly corresponds to strong flares, so it has high value in scientific research and space weather disaster warning.