arXiv subjects

S. A. Trushkin

Publications and source records attributed to S. A. Trushkin.

At least 19 recordsLinked to original sources

arXiv2025

Neural networks in the search for fast radio bursts with RATAN-600

We present a technique to search for fast radio bursts in records obtained with broadband radiometers having few radio channels. The technique is applied to the RATAN-600 surveys carried out at its Western Sector since the year 2017. A 1D convolutional neural network for multichannel time series classification is developed based on the EfficientNet family of models. The procedure to generate synthetic FRB signals needed for the training dataset is described. We implement a two-stage cascade scheme to effectively suppress the rate of false positive detections. Evaluation of the trained model is provided based on the synthetic events and the giant pulse of the Crab Pulsar.

astro-ph.IM↗

arXiv2025

Probing plasma scattering screens towards the quasar 2005+403 with long-term RATAN-600 observations

We continue investigating the observed properties of the quasar 2005$+$403 seen through the highly turbulent plasma in the Cygnus region. Our earlier study Koryukova+2023 revealed a great influence of propagation effects on the observed data, e.g. numerous episodes of multiple imaging formation, angular broadening of the source size, and the detection of an extreme scattering event (ESE) in 2019, making it a good probe for thermal plasma in the interstellar medium (ISM). We report the first detection of multi-frequency and multi-epoch ESEs revealed with the RATAN-600 daily light curves of the quasar 2005$+$403. The most prominent ESE flux density modulations are found in 2011, 2015, and 2020 and each lasted about $4-5$ months. We fitted the detected ESEs jointly at 4.7/4.8, 7.7/8.2, and 11.2~GHz using the models, which allowed us to constrain the angular and linear size of the scattering lens averaged over the three ESEs $0.3\pm0.1$ mas and $0.6\pm0.1$ au, proper motion $8.3\pm0.7$ mas yr$^{-1}$ and transverse velocity $70.1\pm5.7$ km s$^{-1}$ assuming that the lens distance is 1.8 kpc, maximum free-electron density on the line of sight $1183\pm124$ cm$^{-3}$ and lens mass $(0.8\pm0.4)\times10^{-15}\,\rm M_\odot$. Using the fitting results, we reconstructed the intrinsic unscattered angular size of the quasar at the ESE epochs. We also report on the first detection of up to six ESEs in a row that occurred in the period of $2015-2016$, apparently created by multiple lenses successively crossing the line of sight.

astro-ph.GA↗

arXiv2025

Radio and Optical Properties of the blazar PKS 1614+051 at z=3.21

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 almost 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 spectral peak around 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 years) between the radio frequencies along with variability timescales ranging from 0.2 to 1.8 years 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 $\sim\!30$ mG. A spectroscopic study with the BTA SCORPIO-I spectrograph has found signs of the regular motion of a neutral hydrogen envelope around the blazar center, which confirms the presence of enough gaseous matter to form an external FFA screen. The results highlight the importance of multiwavelength and long-term monitoring to understand the physical mechanisms driving the variability in high-redshift blazars.

astro-ph.GA↗

arXiv2024

Radio sources of the survey on the declination of the pulsar in Crab Nebula

The results of the analysis of 205 brightest sources ( $S>15$ mJy), which were found in the sky survey at the declination of the pulsar in the Crab Nebula, are presented. The survey was conducted at a frequency of 4.7~GHz using a three-beam radiometer complex installed in the focus of the Western Sector of the RATAN-600 radio telescope in 2018-2019. Based on the measurements and data collected in the database of astrophysical catalogs CATS built radio spectra of objects. For a quarter of all detected sources, data at a frequency higher than 4~GHz were obtained for the first time, and for the rest, they were appended. The variability of radiation sources on the scales of the year, from days to months, was studied. The greatest change in the radio flux was found in the blazar B2~1324+22. The search for daily variability was carried out for 26 the brightest sources with an average value of $S_{4.7} \sim 250$ mJy. All sources are identified with objects from optical and infrared catalogs. Radio luminosity is calculated for 112 objects with a known redshift.

astro-ph.HE↗

arXiv2024

Multiwavelength variability of the blazar AO 0235+164

We present a study of the multiwavelength (MW) variability of the blazar AO 0235+164 based on the radio-to-$γ$-ray data covering a long time period from 1997 to 2023. The radio data are represented by the 1-22 GHz measurements from the RATAN-600 radio telescope, the 5 and 8 GHz data from the RT-32 telescopes, and the 37 GHz data from the RT-22 telescope. The optical measurements in the $R$-band were collected with the 1-m Zeiss-1000 and 0.5-m AS-500/2 telescopes. Additionally we used the archive data at 230~GHz from the SMA and the $γ$-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. A significant correlation ($\geq\!2σ$) between the radio, optical, and $γ$-ray bands is found for all these periods with time delays from 0 to 1.7 yrs. The relation between time delay and frequency is described by a linear law with a negative slope of -10 day/GHz. The discovered properties of MW variability for the low activity period and for flaring states suggest that the mechanisms dominating the radio-$γ$-ray variations are not substantially different. The detected quasi-periodic oscillations of about 6 and 2 years are tentative, as the time span of the observations includes fewer than 4 full cycles for the radio and optical data and only about 3 cycles for the Fermi-LAT data. 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.

astro-ph.HE↗

arXiv2023

Study of the Cygnus X-3 Microquasar with the RATAN-600 Radio telescope in Multi-Azimuth Observing Mode

We have been performing daily observations of bright microquasars at 1.2-20~GHz with the Northern sector of RATAN-600 radio telescope for more than ten years. During the 2019--2021 observations we recorded bright flares, which we call giant flares because fluxes reach record levels -- above 20~Jy -- during these events. In this paper we report the results of intraday variations of the Cygnus~X-3} microquasar in multi-azimuth observations made with the "North sector with a flat-sheet reflector" during giant flares of Cygnus X-3. These were the first such observations made simultaneously at several frequencies on a short time scale (10 minutes). Observational data consists of 31 measurement made within +/-2.7 hours of the culmination of the object. We are the first to discover the evolution of the spectrum of the flare emission of Cygnus~X-3 on a time scale comparable to the orbital period of the binary. The measurement data allowed us to determine the temporal and spectral parameters of radio emission, which are typical for synchrotron flare emission in relativistic jets. Evolution of the radio emission of X-ray binaries on short time scales is a key to understanding the formation of jet outbursts in the process of mass accretion of the matter of the donor star onto the relativistic object.

astro-ph.HE↗

arXiv2021

Strong low-frequency radio flaring from Cygnus X-3 observed with LOFAR

We present Low-Frequency Array (LOFAR) 143.5-MHz radio observations of flaring activity during 2019 May from the X-ray binary Cygnus X-3. Similar to radio observations of previous outbursts from Cygnus X-3, we find that this source was significantly variable at low frequencies, reaching a maximum flux density of about 5.8 Jy. We compare our LOFAR light curve with contemporaneous observations taken at 1.25 and 2.3 GHz with the RATAN-600 telescope, and at 15 GHz with the Arcminute Microkelvin Imager (AMI) Large Array. The initial 143.5-MHz flux density level, $\sim$2 Jy, is suggested to be the delayed and possibly blended emission from at least some of the flaring activity that had been detected at higher frequencies before our LOFAR observations had begun. There is also evidence of a delay of more than four days between a bright flare that initially peaked on May 6 at 2.3 and 15 GHz, and the corresponding peak ($\gtrsim$ 5.8 Jy) at 143.5 MHz. From the multi-frequency light curves, we estimate the minimum energy and magnetic field required to produce this flare to be roughly 10$^{44}$ erg and 40 mG, respectively, corresponding to a minimum mean power of $\sim$10$^{38}$ erg s$^{-1}$. Additionally, we show that the broadband radio spectrum evolved over the course of our observing campaign; in particular, the two-point spectral index between 143.5 MHz and 1.25 GHz transitioned from being optically thick to optically thin as the flare simultaneously brightened at 143.5 MHz and faded at GHz frequencies.

astro-ph.HE↗

arXiv2018

LOFAR 150-MHz observations of SS 433 and W 50

We present LOFAR high-band data over the frequency range 115-189 MHz for the X-ray binary SS 433, obtained in an observing campaign from 2013 February - 2014 May. Our results include a deep, wide-field map, allowing a detailed view of the surrounding supernova remnant W 50 at low radio frequencies, as well as a light curve for SS 433 determined from shorter monitoring runs. The complex morphology of W 50 is in excellent agreement with previously published higher-frequency maps; we find additional evidence for a spectral turnover in the eastern wing, potentially due to foreground free-free absorption. Furthermore, SS 433 is tentatively variable at 150 MHz, with both a debiased modulation index of 11 per cent and a $χ^2$ probability of a flat light curve of $8.2 \times 10^{-3}$. By comparing the LOFAR flux densities with contemporaneous observations carried out at 4800 MHz with the RATAN-600 telescope, we suggest that an observed $\sim$0.5-1 Jy rise in the 150-MHz flux density may correspond to sustained flaring activity over a period of approximately six months at 4800 MHz. However, the increase is too large to be explained with a standard synchrotron bubble model. We also detect a wealth of structure along the nearby Galactic plane, including the most complete detection to date of the radio shell of the candidate supernova remnant G 38.7-1.4. This further demonstrates the potential of supernova remnant studies with the current generation of low-frequency radio telescopes.

astro-ph.HE↗

arXiv2017

The hypersoft state of Cygnus X-3 - A key to jet quenching in X-ray binaries?

Cygnus X-3 is a unique microquasar in the Galaxy hosting a Wolf-Rayet companion orbiting a compact object that most likely is a low-mass black hole. The unique source properties are likely due to the interaction of the compact object with the heavy stellar wind of the companion. In this paper, we concentrate on a very specific period of time prior to the massive outbursts observed from the source. During this period, Cygnus X-3 is in a so-called hypersoft state, where the radio and hard X-ray fluxes are found to be at their lowest values (or non-detected), the soft X-ray flux is at its highest values, and sporadic gamma-ray emission is observed. We will utilize multiwavelength observations in order to study the nature of the hypersoft state. We observed Cygnus X-3 during the hypersoft state with Swift and NuSTAR in the X-rays and SMA, AMI-LA, and RATAN-600 in the radio. We also considered X-ray monitoring data from MAXI and $γ$-ray monitoring data from AGILE and Fermi. We found that the spectra and timing properties of the multiwavelength observations can be explained by a scenario where the jet production is turned off or highly diminished in the hypersoft state and the missing jet pressure allows the wind to refill the region close to the black hole. The results provide proof of actual jet quenching in soft states of X-ray binaries.

astro-ph.HE↗

arXiv2017

High-energy gamma-ray activity from V404 Cygni detected by AGILE during the 2015 June outburst

The AGILE satellite detected transient high-energy gamma-ray emission from the X-ray binary V404 Cygni, during the June 2015 outburst observed in radio, optical, X-ray and soft gamma-ray frequencies. The activity was observed by AGILE in the 50-400 MeV energy band, between 2015-06-24 UT 06:00:00 and 2015-06-26 UT 06:00:00 (MJD 57197.25 - 57199.25), with a detection significance of ${\sim}4.3σ$. The gamma-ray detection, consistent with a contemporaneous observation by Fermi-LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the 511 keV line emission, possibly indicating plasmoid ejections in a lepton-dominated transient jet. The AGILE observations of this binary system are compatible with a microquasar scenario in which transient jets are responsible for the high-energy gamma-ray emission.

astro-ph.HE↗

arXiv2016

The giant radio flare of Cygnus X-3 in September 2016

In the long-term multi-frequency monitoring program of the microquasars with RATAN-600 we discovered the giant flare from the X-ray binary Cygnus X-3 on 13 September 2016. It happened after 2000 days of the 'quiescent state' of the source passed after the former giant flare (~18 Jy) in March 2011. We have found that during this quiet period the hard X-ray flux (Swift/BAT, 15-50 keV) and radio flux (RATAN-600, 11 GHz) have been strongly anti-correlated. Both radio flares occurred after transitions of the microquasar to a 'hypersoft' X-ray state that occurred in February 2011 and in the end of August 2016. The giant flare was predicted by us in the first ATel #9416. Indeed after dramatic decrease of the hard X-ray Swift 15-50 keV flux and RATAN 4-11 GHz fluxes (a 'quenched state') a small flare (0.7 Jy at 4-11 GHz) developed on MJD 57632 and then on MJD 57644.5 almost simultaneously with X-rays radio flux rose from 0.01 to 15 Jy at 4.6 GHz during few days. The rise of the flaring flux is well fitted by a exponential law that could be a initial phase of the relativistic electrons generation by internal shock waves in the jets. Initially spectra were optically thick at frequencies lower 2 GHz and optically thin at frequencies higher 8 GHz with typical spectral index about -0.5. After maximum of the flare radio fluxes at all frequencies faded out with the exponential law (~ exp(-(t-t0)/2d) for 21.7 GHz).

astro-ph.SR↗

arXiv2010

The Hardness-Intensity Diagram of Cygnus X-3: Revisiting the Radio/X-Ray States

Cygnus X-3 is one of the brightest X-ray and radio sources in the Galaxy, and is well known for its erratic behaviour in X-rays as well as in the radio, occasionally producing major radio flares associated with relativistic ejections. However, even after many years of observations in various wavelength bands Cyg X-3 still eludes clear physical understanding. Studying different emission bands simultaneously in microquasars has proved to be a fruitful approach towards understanding these systems, especially by shedding light on the accretion disc/jet connection. We continue this legacy by constructing a hardness-intensity diagram (HID) from archival Rossi X-ray Timing Explorer data and linking simultaneous radio observations to it. We find that surprisingly Cyg X-3 sketches a similar shape in the HID to that seen in other transient black hole X-ray binaries during outburst but with distinct differences. Together with the results of this analysis and previous studies of Cyg X-3 we conclude that the X-ray states can be assigned to six distinct states. This categorization relies heavily on the simultaneous radio observations and we identify one new X-ray state, the hypersoft state, similar to the ultrasoft state, which is associated to the quenched radio state during which there is no or very faint radio emission. Recent observations of GeV flux observed from Cyg X-3 (Tavani et al. 2009; Fermi LAT Collaboration et al. 2009) during a soft X-ray and/or radio quenched state at the onset of a major radio flare hint that a very energetic process is at work during this time, which is also when the hypersoft X-ray state is observed. In addition, Cyg X-3 shows flaring with a wide range of hardness.

astro-ph.HE↗

arXiv2009

The CATS Service: an Astrophysical Research Tool

We describe the current status of CATS (astrophysical CATalogs Support system), a publicly accessible tool maintained at Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) (http://cats.sao.ru) allowing one to search hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly on catalogs of radio continuum sources observed from 10 MHz to 245 GHz, and secondly on catalogs of objects such as radio and active stars, X-ray binaries, planetary nebulae, HII regions, supernova remnants, pulsars, nearby and radio galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys with non-radio waves. In 2008 CATS comprised a total of about 10e9 records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most source catalogs deriving from observations with the Russian radio telescope RATAN-600. CATS offers several search tools through different ways of access, e.g. via web interface and e-mail. Since its creation in 1997 CATS has managed about 10,000 requests. Currently CATS is used by external users about 1500 times per day and since its opening to the public in 1997 has received about 4000 requests for its selection and matching tasks.

astro-ph.IM↗

arXiv2008

Optical and infrared flares from a transient Galactic soft gamma-ray repeater

Soft gamma-ray repeaters (SGRs) are a rare type of gamma-ray transient sources that are ocasionally detected as bursts in the high-energy sky. They are thought to be produced by magnetars, young neutron stars with very strong magnetic fields of the order of 10^(14-15) G. Only three such objects are known in our Galaxy, and a fourth one is associated with the supernova remnant N49 in the Large Magellanic Cloud. In none of these cases has an optical counterpart to either the gamma-ray flares or the quiescent source been identified. Here we present multi-wavelength observations of a puzzling source, SWIFT J195509+261406, for which we detected more than 40 flaring episodes in the optical band over a time span of 3 days, plus a faint infrared flare 11 days later, after which it returned to quiescence. We propose that SWIFT J195509+261406 is a member of a subgroup of SGRs for which the long-term X-ray emission is transient in nature. Furthermore, it is the first SGR for which bursts have been detected in the optical and near-infrared bands and maybe the link between the "persistent" SGRs and the dim isolated neutron stars.

astro-ph↗

arXiv2007

The 2006 Radio Outburst of a Microquasar Cyg X-3: Observation and Data

We present the results of the multi-frequency observations of radio outburst of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope. Since the prediction of a flare by RATAN-600, the source has been monitored from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the quench of the activity, successive flares exceeding 1 Jy were observed successfully. The time scale of the variability in the active phase is presumably shorter in higher frequency bands. We also present the result of a follow-up VLBI observation at 8.4 GHz with the Japanese VLBI Network (JVN) 2.6 days after the first rise. The VLBI image exhibits a single core with a size of <8 mas (80 AU). The observed image was almost stable, although the core showed rapid variation in flux density. No jet structure was seen at a sensitivity of $T_b = 7.5\times 10^5$ K.

astro-ph↗

arXiv2007

Synchrotron flaring behaviour of CygnusX-3 during the February-March 1994 and September 2001 outbursts

Aims: In this paper we study whether the shock-in-jet model, widely used to explain the outbursting behaviour of quasars, can be used to explain the radio flaring behaviour of the microquasar Cygnus X-3. Method: We have used a method developed to model the synchrotron outbursts of quasar jets, which decomposes multifrequency lightcurves into a series of outbursts. The method is based on the Marscher & Gear (1985) shock model, but we have implemented the modifications to the model suggested by Bjornsson & Aslaksen (2000), which make the flux density increase in the initial phase less abrupt. We study the average outburst evolution as well as specific characteristics of individual outbursts and physical jet properties of Cyg X-3. Results: We find that the lightcurves of the February-March 1994 and September 2001 outbursts can be described with the modified shock model. The average evolution shows that instead of the expected synchrotron plateau, the flux density is still increasing during the synchrotron stage. We also find that high frequency peaking outbursts are shorter in duration than the ones peaking at lower frequencies. Finally, we show that the method can be used, complementary to radio interferometric jet imaging, for deriving the physical parameters such as the magnetic field strength and the energy density of relativistic electrons in the jet of Cyg X-3.

astro-ph↗

arXiv2007

Current status of the CATS database

We describe the current status of CATS, a publicly accessible database (web-server http://cats.sao.ru) allowing one to search in hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly laid on catalogs of radio continuum sources observed from 30 to 15000 MHz, secondly on catalogs of objects such as radio and active stars, planetary nebulae, HII regions, supernova remnants (SNR), pulsars, nearby galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys, like NVSS, FIRST, WENSS, VLSS, TXS, GB6, SUMSS, IRAS, 2MASS, SDSS, ROSAT, PGC, MCG, etc. In 2004 CATS comprised a total of $\sim10^9$ records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most of RATAN--600 catalogs. CATS is being expanded and updated, both with newly published catalogs as well as older ones which we have created in electronic form for the first time. We describe the principles of organization of the database of astrophysical catalogs and the main functions of CATS.

astro-ph↗

arXiv2007

Recent Radio Monitoring of Microquasars with RATAN-600 Radio Telescope

We report about the multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during the period from September 2005 to May 2006. 1. We detected clear correlation of the flaring radio fluxes and X-rays 'spikes' at 2-12 keV emission detected in RXTE ASM from GRS1915+105 during eight relatively bright (200-600 mJy) radio flares in October 2005. The 1-22 GHz spectra of these flares in maximum were optically thick at frequencies lower 2.3 GHz and optically thin at the higher frequencies. During the radio flares the spectra of the X-ray spikes become softer than those of the quiescent phase. Thus these data indicated the transitions from very high/hard states to high/soft ones during which massive ejections are probably happened. These ejections are visible as the detected radio flares. 2. After of the quiescent radio emission we have detected a drop down of the fluxes (~20 mJy) from Cyg X-3. That is a sign of the following bright flare. Indeed such a 1Jy-flare was detected on 3 February 2006 after 18 days of the quenched radio emission. The daily spectra of the flare in the maximum was flat from 1 to 100 GHz, using the quasi-simultaneous observations at 109 GHz with RT45m telescope and millimeter array (NMA) of Nobeyama Radio Observatory in Japan. The several bright radio flaring events (1-10 Jy) followed during this state of very variable and intensive 1-12 keV X-ray emission (~0.5 Crab), which being monitored in RXTE ASM program.

astro-ph↗