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Registration Number

0225U004287, (0125U002181) , R & D reports

Title

Thermal free-free absorption in supernova remnants at radio frequencies below 80 MHz

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Властивості поглинання випромінювання у залишках наднових 3С144, HB3 та 3C461

Head

Stanyslavskyi Oleksandr O., Доктор фізико-математичних наук

Registration Date

28-11-2025

Organization

Radio Astronomical Institute of the National Academy of Sciences of Ukraine

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The purpose of this work is to study the radio emission of supernova remnants 3C144, HB3 and 3C461 from spectral observations using 3C405 as a calibrator. Measurements of such spectra on the Ukrainian GURT and URAN-2 radio telescopes with the French NenuFAR one due to the contribution of ionized gas inside and outside remnants will be a significant result. This will allow us to estimate the temperature, average ionization, and emission measure of the absorbing gas into the remnants and the surrounding interstellar medium.

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Based on the latest achievements of Ukrainian low-frequency radio astronomy, the study of low-frequency spectra of various supernova remnants and the evolution of their radiation over time opens up new possibilities in measuring the properties of thermal absorption in ionized gas inside and outside such radio sources. To conduct high-precision observations of the spectra of supernova remnants, the radiation of the radio galaxy Cygnus A is used as a calibration source, which has an extragalactic origin, a convenient location on the sky and practically does not change in intensity over time. For the reliability of observations, three low-frequency radio telescopes are used in the studies, two Ukrainian, GURT and URAN-2, and one French NenuFAR, which have the appropriate characteristics for conducting measurements. With the help of such observations, we measured the low-frequency spectra of 3C144, HB3, and 3C461. It was found that the full low-frequency spectrum of 3C144 comprises two components: a compact source within the nebula and an extended shell contribution. The shell's flux-density spectrum peaks at 2069 ± 200 Jy near 27.5 ± 0.5 MHz, consistent with a turnover caused by unshocked ejecta. No significant flux of radio emission from this source decrease is detected between 1963 and 2025 within observational uncertainties. This allowed us to determine the values of the free-free absorption parameters in this remnant.

Product Description

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Ihor M. Bubnov
Oleksandr O. Stanyslavsky
Rostyslav V. Vashchyshyn
Lev O. Stanyslavsky
Myrhorod Viacheslav I.

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2025-11-28