Investigation of the Temporal Variations in Scattering and Dispersion Measure of Giant Radio Pulses in the Pulsar В0531+21 in the Crab Nebula at 111 MHz Frequency in 2002–2024

Abstract

We present the results of our monitoring of Giant Radio Pulses (GRPs) of pulsar B0531+21 (J0534+2200) in the Crab Nebula. Observations has been carried in the Pushchino Radio Astronomy Observatory (PRAO) of the Astro Space Center (ASC) of the Lebedev Physical Institute (LPI) using the LPI Large Phased Array (LPA) radio telescope at 111 MHz frequency at band with 2.5 MHz with a 128-channel spectrum analyzer and PRAO Digital Pulsar Receiver in 2002–2024. We show that the dependence between the scattering time \(\tau \) and the dispersion measure \(DM\) of GRPs in the time interval 2010–2021 differs significantly from that before 2010 and after 2021. In 2010–2021, the values of \(\tau \) and \(DM\) demonstrated significant growth and instability, and the functional relationship between them changes rapidly. The data for the entire observation interval forms on plot of {\(\tau ,dm\)} (where \(dm = (DM - 56.7) \times {{10}^{3}}\)) three main and one transitional branches, formed by 14 different time segments. That may be well approximated by power functions \(\tau \propto d{{m}^{n}}\) with values \(n = 0.7\), 1.1, and 1.86 for the main and 2.1 for the transitional branches. This behavior of \(\tau \) and \(DM\) is explained by anomalous variations in the density and turbulence of magnetically active plasma in the Crab Nebula and the interstellar medium in 2010–2021. Comparing the data at 111 and 610 MHz in the MJD interval 55000–56500 (June 2009–July 2013), we obtained an estimate \(\beta = 3.4 \pm 0.2\) for the dependence of observed scattering on the frequency \(\tau \propto {{\nu }^{{ - \beta }}}\). This value is close to the previously published, but significantly differs from the dependencies for both Kolmogorov (\(\beta = 4.4\)) and normal distribution (\(\beta = 4\)) of spatial inhomogeneities of the interstellar medium.