Astronomers have discovered a non-strict periodicity in the repeated fast radio burst FRB 180916. J0158 + 65. The discovery was made based on 28 events recorded from September 2018 to October 2019 by the CHIME telescope. Outbreaks of this source do not occur quite regularly, but on average, a period of 16.35 days can be distinguished with great significance. Observations with various instruments indicate a significant dependence of the flash brightness on the frequency band of observations, says a preprint on the arXiv.org server.
Fast radio bursts (FRBs) are bright bursts of radio emission with a typical duration of about a millisecond. Today, over a hundred such events are known, most of which were single, but about a dozen were observed several times from one area - they are called repeated. At the moment, the nature of FRB remains unknown; this is one of the main mysteries of modern astrophysics.
In 2019, significant progress has been made in the field of FRB research: the list of known events became longer than the list of proposed theoretical models, a single radio burst was localized for the first time, and the first event of this kind was discovered in a relatively nearby galaxy. Many of these advances were made possible by the work of the Canadian CHIME telescope, which has been converted specifically to study FRB.
Now, with the help of this installation, a new discovery has been made: astronomers have discovered the periodicity of the FRB 180916. J0158 + 65 burst, which is still considered the closest to Earth. After analyzing about 400 days of available observations, the scientists were able to confidently identify the recurrence in the appearance of flares with a characteristic period of 16.35 ± 0.18 days. However, the authors of the work note that this pattern is not strict: sometimes an outbreak does not occur, sometimes more than one occurs, and they repeat not tick-to-tick, but within a four-day interval.
In total, the scientists worked with the registration times of 28 bursts. Astronomers have applied several methods of statistical analysis, such as Pearson's goodness-of-fit test, the H-test, which is widely used in astrophysics, and the discrete Fourier transform. As a result, all of them showed repeatability with the same periodicity with a statistical significance of up to 11 standard deviations, which practically excludes the possibility of a chance coincidence.
In addition to CHIME (400-800 megahertz operating band), FRB 180916 was also observed by the European radio interferometric network EVN (operating frequency 1.7 GHz) and at the 100-meter telescope in Effelsberg (operating frequency 1.4 GHz). The first device recorded a burst at the very beginning of the expected period of activity, and the second could not record in a session of simultaneous observations with CHIME, which detected the outbreak at that time. This indicates a significant dependence of brightness on frequency.
Promotional video:
For the first time, the revealed periodicity in the signals of a repeated radio burst may become an important indication of the nature of its source. So far, there are many options, both binary systems (from a pulsar or black hole and ordinary stars of various classes), and solitary objects (magnetars). Future observations will help to better understand the phenomenon, especially if it is possible to record radiation in other ranges of electromagnetic waves, for example, in X-rays or gamma.
Another important tool for studying fast radio spectra is the Australian telescope ASKAP, which doubled the statistics of events known at that time in 2018. More details about fast radio bursts can be found in the review, which was written especially for N + 1 by Sergey Popov, an employee of the Sternberg State Astronomical Institute.
Author: Timur Keshelava