Context. Blazars are a subclass of radio-loud active galactic nuclei (AGN) that display strong multi-wavelength variability on diverse timescales ranging from years down to minutes. In the last 1.5 decades, there have been occasional detections of quasi-periodic oscillations in several blazars in their time series data. Aims. We searched for quasi-periodic oscillations (QPOs) in the 37 GHz radio band light curve of the flat-spectrum radio quasar Ton 599 made at the RT-22 radio telescope in Simeiz, Crimea, from 1990 to 2020. We also searched for QPOs in the available gamma-ray and optical data during the time span of these radio observations. Methods. To identify and quantify the QPO nature of this radio light curve of Ton 599, we used the Lomb-Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses. We performed LSP analyses of the gamma-ray and optical data. Results. We report the detection of a likely QPO of about 2.4 years in a portion of the 37 GHz radio light curve of Ton 599. No QPO signatures of similar timescales were found in either the gamma-ray or optical (R-band) wavebands. Conclusions. We briefly discuss possible emission models for radio-loud AGN that could explain such QPOs with periods of a few years.

The bright blazar OJ 287 has demonstrated a sequence of flares, which are well explained by a quasi-Keplerian orbit model. The flares are associated with the impact of the secondary on the accretion disk of the primary. The orbit must precess in order to produce the correct sequence of flares, and from the precession rate we calculate the mass of the primary. This precession rate gives the mass of the primary M_BH = (18.35±0.05) × 10^9 M_⊙. Two kinds of flares have been identified: direct flares from the impacts, and tidal flares arising from an increased accretion flow into the jet. The precession rate and the primary black hole mass may be independently determined from both sets of flares; the tidal flare of October 2022 was recommended for an intense campaign for this reason. This paper describes these observations over a wide spectral range. We show that the October 2022 flare fits the expectations for a tidal flare and thus supports the earlier determination of the mass of the binary black hole system in OJ 287. The mass of the primary may also be deduced from secondary indicators such as the correlation with the hydrogen line strength and the black hole mass. These studies require that the mass is above M_BH∼ 10^10 M_⊙, but do not specify the value more exactly.

We present a study of the radio and optical properties of the high-frequency peaker (HFP) blazar PKS 1614 + 051 at z=3.21 based on the data covering the time period of 1997–2024. The radio data are represented by the instantaneous 1–22 GHz measurements from the SAO RAS RATAN-600 radio telescope, the 5 and 8 GHz data from the IAA RAS RT-32 telescopes, and the 37 GHz data from the RT-22 telescope of CrAO RAS. The optical measurements in the R band were collected with the SAO RAS 1-m Zeiss-1000 and 0.5-m AS-500/2 telescopes, and the ZTF archive data. We have found low overall variability indices (0.1–0.2) and a median spectral peak at 4.6 GHz, which is stable during the long-term period of monitoring. An analysis of the radio light curves reveals significant time delays (0.6 to 6.4 yrs) between the radio frequencies along with variability timescales ranging from 0.2 to 1.8 yrs in the source’s rest frame, which is similar to the blazars at lower redshifts. Spectral modeling suggests the presence of both synchrotron self-absorption (SSA) and free-free absorption (FFA) processes. Based on the SSA model, we provide estimates of the magnetic field strength which peaks at approximately 100 mG. A spectroscopic study with the BTA SCORPIO-1 spectrograph has found evidence of the regular motion of a neutral hydrogen envelope around the blazar center, which confirms the presence of a sufficient amount of gaseous matter to form an external FFA screen. The results highlight the importance of multi-wavelength and long-term monitoring to understand the physical mechanisms driving the variability in high-redshift blazars.

Using the method of spectral-probability analysis, to evaluate the possibility of predicting an unfavorable outcome of acute decompensation of diabetes mellitus in patients hospitalized in the intensive care unit using a mathematical model. In relation to clinical practice, the implementation of the proposed algorithm for mathematical processing of a set of test data provides the physician with an additional significant criterion for assessing the probability of a tendency to develop type 1 diabetes in healthy children being examined whose brothers or sisters suffer from this disease. A retrospective analysis of 103 medical records of patients hospitalized in the intensive care unit for acute decompensation of diabetes mellitus was conducted. With regard to the set of analyses of patients with acute decompensation of diabetes mellitus, carried out at the time of admission to hospital, a group of mathematical criteria has been defined that makes it possible to identify patients with a high risk of an unfavorable course of the disease.

A new technique for determining the precursors of an upcoming strong seismic event causing a tsunami is considered, based on the occurrence of the effect of topological similarity of statistical functionals L(n) from magnetic field measurements. The measurements were carried out using data from spatially distant magnetic standard observatories in Japan (KNY, KAK and MMB) before the earthquake of magnitude 7.3 on 03/16/2022 at 14:37 UTC in the Pacific Ocean near the central part of the Japanese Islands. For stations KNY, KAK and MMB, the minimum of the dependencies L(n) for the X- and Y-components, and stations KNY and MMB for the Z-component of the magnetic field, correspond to the time interval of 62–69 hrs before the event. This phenomenon can be used as a ‘regular’ (i.e., repeated with high probability) harbinger of approaching earthquakes that cause tsunamis.

Aims. A new method of determining the parameters of close binary systems of supermassive black holes (SMBHs) and the level of gravitational waves (GWs) on the Earth's surface are proposed. Methods. Data are presented from long-term monitoring of possibly the most powerful emitter in the Universe, S 0528+134, at five frequencies in the radio range from 4.8 GHz to 37 GHz, obtained by the RT-22 radio telescope of the Radio Astronomy Laboratory CrAO in Simeiz, the RT-26 radio telescope at Michigan Observatory, and the 40 m radio telescope of the Owens Valley Radio Observatory. Results. The dynamics of powerful flares that have occurred in the object since its discovery in a sky survey in 1970 were considered. The main physical characteristics of binary SMBHs located in the central regions of the system were obtained. These data were used to find the masses of the SMBH companions, the parameters of their orbits, the energy reserve of the system, and the lifetime of the object before the SMBHs' merger. The level of GWs on the Earth's surface was determined and the possibility of their detection by International Pulsar Timing Array (IPTA) GW detectors was considered.

We report new data on AO 0235+164, obtained under the program of long-term multifrequency monitoring of active galactic nuclei (AGNs). A model is proposed for finding the parameters of close binary systems of supermassive black holes (SMBHs) by using only observational data in the radio range. The methodology for determining the physical characteristics of the SMBHs includes harmonic and wavelet analyses as well as the assessment of the masses of the satellites and their orbital characteristics. It is shown that AO 0235+164 can be a very massive and close binary system containing companions with similar masses. The presence of an orbital period and a multiple half-period indicates the absence of noticeable eccentricity in the system. Estimates show that, along with such AGNs as 3C 454.3 and OJ 287, AO 0235+164 can be a high-power gravitational wave (GW) emitter accessible for detection by gravitational wave detectors such as the International Pulsar Timing Array (IPTA).

Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65 + 1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65 + 1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered. The active galactic nucleus S 0528 + 134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528 + 134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528 + 134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528 + 134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors.

We examine lengthy radio light curves of the flat spectrum radio galaxy 3C 454.3 for possible quasiperiodic oscillations (QPOs). The data used in this work were collected at five radio frequencies, 4.8, 8.0, 14.5, 22.0, and 37.0 GHz between 1979 and 2013 as observed at the University of Michigan Radio Astronomical Observatory, Crimean Astrophysical Observatory, and Aalto University Mets & auml;hovi Radio Observatory. We employ generalized Lomb-Scargle periodogram and weighted wavelet transform analyses to search for periodicities in these light curves. We confirm a QPO period of similar to 2000 days to be at least 4 sigma significant using both methods at all five radio frequencies between 1979 and 2007, after which a strong flare changed the character of the light curve. We also find a similar to 600 day period, which is at least 4 sigma significant, but only in the 22.0 and 37.0 GHz light curves. We briefly discuss physical mechanisms capable of producing such variations.

We present a study of the multiwavelength (MW) variability of the blazar AO 0235+164 based on the radio-to-gamma-ray data covering a long time period from 1997 to 2023. The radio data are represented by the 1-22 GHz measurements from the SAO RAS RATAN-600 radio telescope, the 5 and 8 GHz data from the IAA RAS RT-32 telescopes, and the 37 GHz data from the RT-22 telescope of CrAO RAS. The optical measurements in the R-band were collected with the SAO RAS 1-m Zeiss-1000 and 0.5-m AS-500/2 telescopes. Additionally, we used the archive data at 230 GHz from the Submillimetre Array and the gamma-ray data in the 0.1-100 GeV band from the Fermi-LAT point source 4FGL-DR2 catalogue. The variability properties during four epochs containing major flares and one epoch of relatively low activity were analysed using the fractional variability indices, discrete correlation functions, Lomb-Scargle periodograms, and structure functions. A significant correlation (>= 2 sigma) between the radio, optical, and gamma-ray bands is found for all these periods with time delays from 0 to 1.7 yr. The relation between time delay and frequency is described by a linear law with a negative slope of -10 d GHz(-1). The discovered properties of MW variability for the low-activity period and for flaring states suggest that the mechanisms dominating the radio-gamma-ray variations are not substantially different. The detected quasi-periodic oscillations of about 6 and 2 yr are tentative, as the time span of the observations includes fewer than four full cycles for the radio and optical data and only about three cycles for the Fermi-LAT data. These results should be interpreted with caution, given the limited number of observed cycles and the influence of red noise. We used cluster analysis to reliably separate the high and low-activity states and determined statistical differences in the main properties of AO 0235+164 non-thermal emission. The physical parameters of the radio jet were obtained using the Hedgehog model applied to the average radio spectrum of AO 0235+164 in the range 0.1-300 GHz. The effectiveness of replacing electrons with protons in the synchrotron radio emission of relativistic jets is shown for describing the nature of blazars and the generation of high-energy neutrinos.

We present an optical-to-radio study of the BL Lac object S4 0954+658 observations during 1998–2023. The measurements were obtained with the SAO RAS Zeiss-1000 and AS-500/2 0.5-m telescopes in 2003–2023, with the RATAN-600 radio telescope at 1.25 (0.96, 1.1), 2.3, 4.7 (3.7, 3.9), 8.2 (7.7), 11.2, 22.3 (21.7) GHz in 1998–2023, with the IAA RAS RT-32 Zelenchukskaya and Badary telescopes at 5.05 and 8.63 GHz in 2020–2023, and with the RT-22 single-dish telescope of CrAO RAS at 36.8 GHz in 2009–2023. In this period the blazar was showing extremely high broadband activity with the variability amplitude of the flux densities up to 70–100 % both in the optical and radio domains. During the period of 2014–2023 the blazar displayed extremely high activity in the radio wavelengths, and we detected multiple radio flares of varying amplitude and duration. The large flares last on average from 0.3 to 1 year at 22–36.8 GHz and slightly longer at 5–11.2 GHz. The optical flares are shorter and last 7–50 days. The characteristic time scale τ of variation at 5–22 GHz is about 100 days in the most active epoch of 2014–2023 and about 1000 days for the state with lower activity in 2009–2014. We found a general correlation between the optical, radio, and γ -ray flux variations, which suggesting that we observe the same photon population from different emission regions. We estimated the linear size of this region as 0.5–2 pc for different conditions. A broadband radio spectrum with two components of the S4 0954+658 jet was modeled using both electrons and protons as emitting particles. The results suggest that the synchrotron radio waves in this AGN may be produced by relativistic protons.

In this work, it is shown that early warning signals were recorded prior to a 6.4 magnitude earthquake that took place on December 29, 2020, near the Croatian city of Petrinja. The study relied on analyzing property changes in small-scale probability density fluctuations in three parameters of the Earth’s magnetic field: X, Y and Z. The applied technique made it possible to identify a set of these precursors in intervals ranging from two and a half days to one day to less than one hour before this event. It has been observed that the three magnetic variation stations located at distances of approximately 300, 1000, and 1500 km from the epicenter exhibit significant differences in the occurrence of early warning signs and critical phenomena during an impending earthquake. These differences are related to the intensity and frequency of the effects observed at each station.

ABSTRACT We present full photometric coverage and spectroscopic data for soft gamma-ray burst GRB 201015A with a redshift z = 0.426. Our data span a time range of 85 d following the detection of GRB. These observations revealed an underlying supernova SN 201015A with a maximum at 8.54 ± 1.48 d (rest frame) and an optical peak absolute magnitude $-19.45_{-0.47}^{+0.85}$ mag. The SN stands out clearly, since the contribution of the afterglow at this time is not dominant, which made it possible to determine SN’s parameters. A comparison of these parameters reveals that the SN 201015A is the earliest (the minimum Tmax) known SN associated with GRBs. Spectroscopic observations during the SN decay stage showed broad lines, indicating a large photospheric velocity, and identified this SN as a Type Ic-BL. Thus, the SN 201015A associated with the GRB 201015A becomes the 27th SN/GRB confirmed by both photometric and spectroscopic observations. Using the results of spectral analysis based on the available data of Fermi-GBM experiment, the parameters Ep,i = 20.0 ± 8.5 keV and Eiso = (1.1 ± 0.2) × 1050 erg were obtained. According to the position of the burst on the Ep,i–Eiso correlation, GRB 201015A was classified as a type II (long) GRB, which was also confirmed by the T90,i–EH diagram.

This paper presents a numerical analysis, using the rigorous-coupled-wave-analysis method, of microwave and far-IR radiation scattering on thin conductive films of nanometer thickness under the condition of total internal reflection. Transmittance, reflection, and absorption studies have shown the possibility of overcoming the 50% absorption limit with frequency-independent behavior; the absorption above the critical angle reaches values greater than 90%. In addition, the influence of such thin metal-dielectric structure on the Goos–Hänchen shift is considered. At maximum absorption, calculations showed its absence in both TE and TM polarizations. The numerical analysis was carried out for a plane wave and for a 500 cm diameter beam.

The paper considers the properties of statistical function whose plot comprises a set of measurements of H-component of the magnetic field. There has been found a set of quasi-linear objects with very similar parameters. In the context of a hypothesis about the correspondence of these structures to seismic processes, there has been made an estimate of time intervals typical for the phases of decrease and increase in the level of compression of lithospheric plate material in the earthquake source zones. It has been shown that the application of statistical methods in geophysics may contribute to near real-time assessment of seismic hazard in the study area.

We studied the process of energy release of the confined X2.2 flare, which occurred September 6, 2017 in the active region NOAA 12673. The magnetic reconnection rate and reconnection fluxes were obtained from chromospheric data (SDO/AIA 1600 Å) and magnetograms of the photospheric field (SDO/HMI). The time profiles of the magnetic reconnection rate and microwave emission obtained by the radioastronomical diagnostic complex of solar activity of the Crimean Astrophysical Observatory, Russian Academy of Sciences (KRIM) demonstrate good agreement. This suggests that the magnetic reconnection rate plays an important part in the energy release in flares and in the acceleration of nonthermal electrons with formation of microwave emission. The morphology of the flare radio source in low-frequency emission has been studied. The low-frequency slope of the flux density spectrum is 1.2, which indicates a spatial inhomogeneity of the source. The area of such a source increases with a decrease in frequency.

We analyzed the dynamics of the reconnection and energy release processes of the X2.2 and X9.3 flares that occurred on September 6, 2017 in the active region NOAA 12673. We used SDO /AIA 1600 Å images together with SDO /HMI magnetograms. As a proxy for the flare energy release rate, we used the KRIM and RSTN microwave time profiles, GOES soft X-rays and its time derivative. Assuming that the chromospheric flare ribbons are located at the footpoints of magnetic field lines reconnecting in the corona and that the magnetic flux is conserved from the photosphere to the corona, we obtained magnetic reconnection fluxes and rates of its change. The cumulative positive and negative magnetic fluxes involved in the reconnection process were balanced. Temporal correlations are found between the calculated reconnection rate and the observed microwave emissions from for both events. An analysis of the total cumulative magnetic flux and SXR fluence of events showed that the magnitude of the magnetic flux involved in the reconnection process was greater in more energetic events and less in weaker ones.

We present the measurement results for the spectral flux densities of 19 calibration sources observed with the RT-22 single-dish telescope of the Crimean Astrophysical Observatory of the Russian Academy of Sciences at 22.2 and 36.8 GHz in 2017–2020. About half of them belong to the commonly accepted secondary standards with periodically monitored flux densities at radio frequencies. The measurements were carried out to refine the calibration measurements of the RATAN-600 radio telescope at high frequencies. The specificity of RATAN-600 meridian observations requires a ‘‘grid’’ of calibration objects distributed over declinations from $$-35^{\circ}$$ to $$+90^{\circ}$$ instead of 1–3 conventional calibrators which are sufficient for observations at different heights with a single-dish antenna. The radio variability of the objects was estimated taking into account the literature measurements, the results were interpolated to a frequency of 30 GHz. It was found that radio variability at 22 GHz at time scales of about 20–30 years exceeds 10 $$\%$$ for the calibrators 4C $$+$$ 16.09 and 3C 309.1. We discuss a possibility of verifying the calibration sources at the RT-22 by a new method that uses a noise signal generator as an indicator of their relative flux density accuracy.

We perform correlation and periodicity search analyses on long-term multi-band light curves of the FSRQ 1510-089 observed by the space-based Fermi--Large Area Telescope in gamma-rays, the SMARTS and Steward Observatory telescopes in optical and near-infrared (NIR) and the 13.7 m radio telescope in Metsahovi Radio Observatory between 2008 and 2018. The z-transform discrete correlation function method is applied to study the correlation and possible time lags among these multi band light curves. Among all pairs of wavelengths, the gamma-ray vs. optical/NIR and optical vs. NIR correlations show zero time lags; however, both the gamma-ray and optical/NIR emissions precede the radio radiation. The Generalized Lomb-Scargle periodogram, Weighted Wavelet Z-transform, and REDFIT techniques are employed to investigate the unresolved-core-emission dominated 37 GHz light curve and yield evidence for a quasi-period around 1540 days, although given the length of the whole data set it cannot be claimed to be significant. We also investigate the optical/NIR color variability and find that this source shows a simple redder-when-brighter behavior over time, even in the low flux state.

ABSTRACT As a result of detailed observations of the water vapour maser at the 22-m Simeiz radio telescope from 2017 June to 2019 December, two powerful flares were recorded in the Galactic source W49N, which occurred near the high-velocity feature −40 km s−1. The extremely powerful flare had an ultrashort duration of about 2 d and reached a flux density of 110 kJy. An ultrashort flare occurred at the top of a less powerful, but ten times longer one. To our knowledge, a flare of a water maser with such extreme characteristics has never been reported before. A correlation between the exponential increase and decrease in the flare flux density and decrease in line widths with increasing flux density, which is characteristic of an unsaturated maser, is found. The maser of the third flare was in a saturated state and provided a large input flux density 9.5 kJy for the occurrence of two powerful flares, the masers of which were in an unsaturated state. New data have been obtained concerning the physical characteristics of the water maser phenomenon during powerful flares.