Fine frequency structure of interstellar scintillation pattern in radio emission of the PSR B1133+16 at 111 MHz

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Abstract

The B1133+16 pulsar was observed at a frequency of 111 MHz with the LPA PRAO radio telescope from October 2022 to March 2023. Observations were made twice a week for two days in a row. In total 38 measurements of the scattering parameters were carried out with a high frequency resolution (up to 65 Hz). We used continuous recording of voltage in the frequency band 2.5 MHz with 8-bit digitization. The signal was reconstructed using the coherent dedispersion method. Dynamic spectra (DSP) were constructed for each observing session. Then, for each DSP, we calculated a two-dimensional autocorrelation function (2DACF) and analyzed its frequency and time sections. We have studied the fine frequency structure of pulsar scintillations by analyzing both the dynamic spectra, and the spectra of individual pulses. It has been found that the intrinsic shape of diffraction distortion on average can be represented by a sharp two-sided function with a characteristic frequency width of 1–2 kHz. The long-term variability of the following parameters has been carefully studied: characteristic scales in frequency and time ( fdif and tdif), and rotation measure RM. Based on the analysis of long-term variations, it is suggested that the true frequency form of scintillations may be distorted by ionospheric effects. We also compared the scintillation parameters separately for the two mean profile components, and no differences between the parameters were found.

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About the authors

M. V. Popov

P. N. Lebedev Physical Institute of the Russian Academy of Sciences

Email: popov069@asc.rssi.ru

Astrospace Center

Russian Federation, Moscow

T. V. Smirnova

P. N. Lebedev Physical Institute of the Russian Academy of Sciences

Author for correspondence.
Email: tania@prao.ru

Pushchino Radio Astronomy Observatory

Russian Federation, Pushchino

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Supplementary files

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2. Fig. 1. Examples of average profiles in individual observation sessions. The temporal resolution is 0.2 ms.

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3. Fig. 2. Examples of dynamic spectra for 4 days of observations. The intensity scale is presented in arbitrary units. The columns to the right of the spectra correspond to the gradation of the signal intensity. The x-axis shows the frequency in MHz, and the y-axis shows the pulse number (time).

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4. Fig. 3. Examples of frequency cross-sections of two-dimensional autocorrelation functions (2DACF). The solid lines on the left side of the figure represent sinusoidal curves due to the Faraday rotation of the plane of linear polarization in the receiver band, and the dashed lines correspond to the average value of the sinusoidal wave. The right panels of the figure show the approximation of the frequency cross-section by the generalized exponential function Y(x).

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5. Fig. 4. Functions averaged over the entire observation period. At the top is the average ACF in a wide range of frequency shifts, in the center is its central part (the value at zero frequency shift is eliminated). At the bottom is the time section of the average 2DACF with the following parameters: Pf = 5.7 ± 0.1 MHz; fdif = 5.2 ± 0.1 kHz;  = 0.95 ± 0.01; tdif = 45.0±1.7 s.

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6. Fig. 5. Comparison of the time and frequency sections of the ACF and CCF for two components of the mean profile. The parameters obtained by approximating the corresponding functions are given in Table 2.

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7. Fig. 6. Selected strong individual pulses recorded during the observing session on February 6, 2023. The pulses are shown with a time resolution of 20 μs.

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8. Fig. 7. Autocorrelation functions (ACF) obtained for the spectra of individual components of the average profile, and cross-correlation functions (CCF) between the spectra of individual components. They were obtained for individual pulses in the session of February 2, 2023 and are presented in Fig. 6.

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9. Fig. 8. Results of numerical modeling of spectra. The upper left figure is an individual pulse recorded in the session on December 9, 2022 under number 58; the upper right figure is the power spectrum for this pulse (the first component); in the middle left is the ACF for the power spectrum of pulse No. 58; in the middle right is the simulated spectrum; in the lower part of the figure is the ACF from the simulated spectrum.

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10. Fig. 9. Comparison of the ensemble-averaged ACF frequency cross-section (dashed line) and the corresponding ensemble-averaged scintillator eigenfrequency form (solid line). These functions were calculated according to equation (5) for the parameters specified in the text.

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