PERIODIC AND SPORADIC VARIATIONS IN THE SPECTRAL FLUX DENSITY OF THE CAS A SUPERNOVA REMNANT

DOI: https://doi.org/10.15407/rpra25.04.268

A. A. Gorbunov, M. I. Ryabov, A. L. Sukharev, V. V. Bezrukovs

Abstract


Purpose: Based on the long-term study data in all radio spectrum ranges, the nature of deviations of spectral flux density of the Cas A supernova remnant from the tendency of its secular decrease is considered. The aim of this work is determining the presence of quasiperiodic variations and sporadic changes in the Cas A spectral radiation flux density depending on frequency.

Design/methodology/approach: The main database is using the published results obtained with the method of absolute measurements of the Cas A spectral radiation flux density in a wide range from millimeter to decimeter wavelengths, as well as the results obtained with the method of relative measurements of the ratio of the flux densities of the Cas A supernova remnant and radio galaxy Cyg A, this latter being used as a reference source in the meter wavelength range. For making comparison with the aforesaid data obtained with different methods, the results of a long-term monitoring (since 1987) of the variation of the ratio of the spectral flux densities of Cas A and Cyg A made with the URAN-4 radio telescope of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine at 25 MHz were used.

Findings: As a result of the analysis of the observed data for the Cas A radiation flux density in the entire radio wavelength range, the existence of quasiperiodic variations in the range from millimeter to meter wavelengths within 2 to 9 years has been noted. The reason for the detected quasiperiodic variations can be the processes in the Cas A remnant itself. In the decameter wavelength range, according to monitoring data obtained with the URAN-4 radio telescope, the seasonal-diurnal and long-term variations are noted, being associated with changes in the ionosphere state in the solar activity cycle, with some weak appearance of the secular decrease of the Cas A radiation flux. The presence of sporadic variations in the ratio of the spectral flux densities of Cas A and Cyg A is associated with the effect of the increased solar activity. For explaining the lowering of the Cas A spectral flux density to the Cyg A level and maintaining the excess of the Cas A flux at decameter waves, the quasi-simultaneous observations made with radiotelescopes for different wavelength ranges will be required.

Conclusions: The evolution of the Cas A supernova remnant remains the focus of interest of current research efforts. An intriguing moment was the discovery of a point X-ray source in the center of radio source Cas A as a possible supernova remnant. The role of this source in the Cas A radio flux secular decrease and in its variations needs to be clarified. A detailed analysis of the long-term data and making quasi-simultaneous observations will allow to reveal the processes occurring in the radio source itself and to determine the influence of the ionosphere state on the results of measurements. A joint program is suggested for observations of Cas A and Cyg A flux variations with the RT-32 and RT-16 radio telescopes, the LOFAR element of the Ventspils International Radio Astronomy Center (Latvia), and the URAN, UTR-2 and GURT radio telescopes of the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine. 

Key words: Cas A; secular radiation flux decrease; supernova remnant; ionosphere; solar activity

Manuscript submitted 08.11.2020

Radio phys. radio astron. 2020, 25(4): 268-275

REFERENCES

1. BAARS, J. W. M., GENZEL, R., PAULINY-TOTH, I. I. K. and WITZEL, A., 1977. The Absolute spectrum of Cas A: An Accurate Flux Density Scale and Set of Secondary Calibrators. Astron. Astrophys. vol. 61, is. 1, pp. 99–106.

2. STANKEVICH, K. S., IVANOV, V. P. and STOLYAROV, S. P., 1999. Fifty Years of Radio Observations of the Discrete Source Cassiopeia A. Astron. Lett. vol. 25, is. 8, pp. 501–507.

3. BARABANOV, A. P., IVANOV, V. P., STANKEVICH, K. S. and STOLYAROV, S. P., 1986. Evolution of the Cassiopeia A radio spectrum: evidence for cyclic variability. Sov. Astron. vol. 30, is. 5, pp. 549–554.

4. IVANOV, V. P. and STANKEVICH, K. S., 1989. Periodic variations of the radio emission and evolution of the spectrum of the supernova remnant Cassiopeia A. Sov. Astron. vol. 33, is. 1, pp. 15–20.

5. TROTTER, A. S., REICHART, D. E., EGGER, R. E., STÝBLOVÁ, J., PAGGEN, M. L., MARTIN, J. R., DUTTON, D. A., REICHART,J. E.,. KUMAR, N. D, MAPLES, M. P., BARLOW, B. N., BERGER, T. A., FOSTER, A. C., FRANK, N. R., GHIGO, F. D., HAISLIP, J. B., HEATHERLY, S. A., KOUPRIANOV, V. V., LACLUYZÉ, A. P., MOFFETT, D. A., MOORE, J. P., STANLEY, J. L. and WHITE, S., 2017. The fading of Cassiopeia A, and improved models for the absolute spectrum of primary radio calibration sources. Mon. Not. R. Astr. Soc. vol. 469, is. 2, pp. 1299–1313. DOI: https://doi.org/10.1093/mnras/stx810

6. VINYAIKIN, E. N., 2007. Evolution of the radio spectrum of Cassiopeia A from long-term observations. Observations at 290 and 927 MHz. Astron. Rep. vol. 51, pp. 87–96. DOI: https://doi.org/10.1134/S1063772907020023

7. VINYAIKIN, E. N., 2014. Frequency dependence of the evolution of the radio emission of the supernova remnant Cas A. Astron. Rep. vol. 58, pp. 626–639. DOI: https://doi.org/10.1134/S1063772914090078

8. MARTIROSSYAN, R. M., GOULYAN, A. G., SANAMYAN, V. A. and MANASELYAN, KH. A., 2020. Flux density variations of Cassiopea A radio source. Astrofizika. vol.45, no. 3, pp. 443–449. (in Russian).

9. HELMBOLT, J. F. and KASSIM, N. E., 2009. The Evolution of Cassiopeia A at Low Radio Frequencies. Astron. J. vol. 138, is. 3, pp. 838–844. DOI: https://doi.org/10.1088/0004-6256/138/3/838

10. WALCZOWSKI, L. T. and SMITH, K. L., 1985. A recurrence of the Cassiopeia A flux anomaly. Mon. Not. R. Astron. Soc. vol. 212, is. 1, pp. 27P–31P. DOI: https://doi.org/10.1093/mnras/212.1.27P

11. RYABOV, M. I., PANISHKO, S. K. and GUGLYA, L. I., 2011. Space weather impacts on the Earth’s upper atmosphere according to the monitoring of powerful radio sources fluxes at the URAN-4 radio telescope (Institute of Radio Astronomy, NAS of Ukraine). Odessa Astronomical Publications. vol. 24, pp. 159–161. (in Russian).

12. GORBYNOV, A. A., RYABOV, M. I. and PANISHKO, S. K. 2015. Secular Decrease the Flux of Supernova Eemnant Cas A on Monitoring Results to Radiotelescope “URAN-4” IRA NASU. Odessa astronomical publications. vol. 28, no. 2, pp. 224–226. DOI: https://doi.org/10.18524/1810-4215.2015.28.71013

13. RYABOV, M. I. and SEROKUROVA, N. G., 1993. On the secular decrease of the radio flux Cas A at low frequencies. Astron. Astrophys. Trans. vol. 4, is. 1, pp. 29–32. DOI: https://doi.org/10.1080/10556799308205353



Keywords


Cas A; secular radiation flux decrease; supernova remnant; ionosphere; solar activity

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