Scientific achievements. Metagalaxy

2024

Six- and Two-Year Quasi-Periods of Long-Term Variability of the Blazar AO 0236+164 Determined for the First Time from Multiwavelength Observations

The multiwavelength properties of the emission variability of the blazar AO 0235+164 are presented on a 27-year time scale from 1997 to 2023. The measurements were made with the RATAN-600 telescopes (SAO RAS) in the range of 1-22 GHz, RT-32 (IAA RAS) at 5 and 8 GHz, and RT-22 (CrAO RAS) at 37 GHz. In the submillimeter range, the SMA data at 230 GHz were used, in the γ-range (0.1-100 GeV) — Fermi-LAT. Measurements in the optical range (the R band) were obtained with the SAO RAS Zeiss-1000 and AS-500/2 telescopes. For the analysis, the light curves are divided into 4 epochs, each associated with one major flare, with a low-state epoch in 2009-2014 highlighted separately. Correlations between the radio, optical, and γ-ranges are found in all 4 activity epochs with delay times of up to 1.7 years (significance ≥2σ). A linear relationship was found between frequency and delay time with a slope of about −10 days/GHz, which means that the flare starts and develops at high frequencies followed by spreading to lower frequencies. During the period of low activity in 2009-2014, the variability in the optical and γ-ranges reaches 30 and 50%, which may be caused by the interaction of shock wave remnants that followed large bursts. The correlation between the radio, optical, and γ-ray light curves found for this period for the first time may indicate that the mechanisms causing the low-state emission variability are no different from those of the active phase.

The Lomb-Scargle periodograms calculated taking into account the influence of red noise revealed the presence of quasi-periods of about 6 years (up to 4σ) at all wavelengths in the period of 1997-2023. For the quiescent-state epoch, a period of about 2 years (≥2-3σ) was detected for the first time. The quasi-period of 6 years may reflect the time between the most noticeable flares in the light curves, which may have a stochastic nature, and the detected quasi-periodicity has no close relationship with the characteristics of the active nucleus and the relativistic jet. However, we suggest that the periodicity detected for the low state reflects the basic properties of the AGN in AO 0235+164.

Authors:
Vlasyuk V.,¹ Sotnikova Yu.,^1,2 Volvach A.,³ Mufakharov T.,^1,2 Kovalev Yu.A.,^4,5 Spiridonova O.,¹ Khabibullina M.,¹ Kovalev Yu.Yu.,⁶ Mikhailov A.,¹ Stolyarov V.,¹ Kudryavtsev D.,¹ Mingaliev M.,^1,2,7 Razzak S.,⁸ Semenova T.,¹ Kudryashova A.,¹ Bursov N.,¹ Trushkin S.,¹ Popkov A.,^4,9 Erkenov A.,¹ Rakhimov I.,⁷ Kharinov M.,⁷ Gurwell M.,¹⁰ Tsybulev P.,¹ Moskvitin A.,¹ Fatkhullin T.,¹ Emelyanov E.,¹ Arshinova A.,¹ Yuzhanina K.,¹ Andreeva T.,⁷ Volvach L.,³ Ghosh A.^8
1SAO RAS, ²KFU, ³CrAO RAS, ⁴ASC LPI, ⁵INR RAS, ⁶MPIfR, ⁷IAA RAS, ⁸University of Johannesburg, ⁹MIPT, ¹⁰Harvard-Smithsonian Center for Astrophysics
Details

Published:
Vlasyuk V. V. et al., Multiwavelength variability of the blazar AO 0235+16, MNRAS, 2024, Volume 535, Issue 3, Pages 2775-2799

Detection and Study of Five Giant Flares of the Microquasar Cyg X-3 in 2024

In February-August 2024, during regular multi-frequency (1-30 GHz) monitoring with the SAO RAS RATAN-600 radio telescope, five giant (above 10 Jy) flares from the unique X-ray binary Cygnus X-3, which includes a black hole (BH) and a Wolf-Rayet star, were detected. In such rare flares, Cygnus X-3 became the brightest radio source in the Milky Way, not counting several remnants of historical supernovae. It was found that the onset of each of the five flares was unambiguously associated with the detection of significant high-energy gamma radiation in the range of 0.1-300 GeV by the Fermi space observatory. All flares occurred during the transition of the system from the hyper-soft X-ray state to the hard state, when hard X-ray emission (Swift/BAT, 15-50 keV) arose and the soft radiation flux (MAXI, 4-10 keV) dropped sharply. We explain this behavior within the framework of a physical picture with a changing and, as was recently revealed in X-ray polarization measurements at the IXPE observatory, supercritical rate of the matter accretion onto the BH, the state of the hot corona and accretion disk, and the processes of formation and collimation of jet emissions. The radio outbursts evolved on different scales from 10 to 60 days and had similar properties: in the first hours, the radio flux grew linearly with time, more slowly at low frequencies; after two to three days, there was an exponential attenuation with a gradual softening of the radio spectrum (the spectral index changed from −0.1 to −0.9). Such specific properties clearly indicated the generation of synchrotron radio emission by relativistic electrons in jet ejections. In turn, these electrons, scattering the optical radiation of the star in the process of inverse Compton scattering, led to the generation of high-energy gamma rays. On average, the flare radio emission released a huge amount of energy, about 10³⁹ J. The spectra of the onset of the June flare with a characteristic dip at frequencies below 3 GHz, probably caused by thermal electrons in the jets, were obtained. For the first time in the world, it was possible to study in detail the spectral and temporal variability of Cyg X-3 at times from 9 to 300 minutes in a new fast-shift mode at the “Southern sector with a flat reflector” antenna system of RATAN-600 at two frequencies of 4.7 and 8.2 GHz.

Authors:
Trushkin S.A., Shevchenko A.V., Bursov N.N., Nizhelskij N.A., Tsybulev P.G. (SAO RAS)

Published:
1. Veledina et al., Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE, Nature Astronomy, Volume 8, p. 1031-1046
2. Trushkin S., Shevchenko A., Bursov N., Nizhelskij N., Tsybulev P., The flaring activity of microquasars is the key to understanding the processes of accretion and generation of jet emission, Modern astronomy: from the Early Universe to exoplanets and black holes, Proceedings of the VAK-2024 conference, Aug 25–31, 2024 — Moscow, RIOR, 2024, ISBN 978-5-369-02160-6
Details