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 with the quenched radio state during which there is no or very faint radio emission. Recent observations of GeV flux observed from Cyg X-3 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.
The AGILE satellite detected transient high-energy γ-ray emission from the X-ray binary V404 Cygni, during the 2015 June outburst observed in radio, optical, X-ray, and soft γ-ray frequencies. The ...activity was observed by AGILE in the 50-400 MeV energy band, between 2015 June 24 UT 06:00:00 and 2015 June 26 UT 06:00:00 (MJD 57197.25-57199.25), with a detection significance of ∼4.3 . The γ-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 γ-ray emission.
ABSTRACT
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, ∼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 4 d between a bright flare that initially peaked on May 6 at 2.3 and 15 GHz, and the corresponding peak (≳ 5.8 Jy) at 143.5 MHz. From the multifrequency light curves, we estimate the minimum energy and magnetic field required to produce this flare to be roughly 1044 erg and 40 mG, respectively, corresponding to a minimum mean power of ∼1038 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.
The paper presents results of calculating the RATAN-600 beam pattern (BP) and BP drift scans of point radio sources in the West Sector radio telescope operation mode at a frequency of 4.7 GHz. When ...calculating the BP, the properties of the radio telescope antenna system in this operation mode were taken into account: the use of a large secondary mirror, asymmetric radiation of the primary mirror, and the location of the primary feeds (feed horns) along the focal line of the secondary mirror. The shape of the calculated drift scans of sources through the BP is compared with that of the experimental drift scans of sources obtained from observations in the West Sector. The main characteristics of the drift scans are calculated and compared when the radio telescope operates with the West and North Sectors. A new method for determination of flux densities of sources passing through the BP outside its central cross-section is proposed, and its accuracy is estimated.
LOFAR 150-MHz observations of SS 433 and W 50 Broderick, J W; Fender, R P; Miller-Jones, J C A ...
Monthly Notices of the Royal Astronomical Society,
04/2018, Letnik:
475, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
We present Low-Frequency Array (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 to 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 χ2 probability of a flat light curve of 8.2 × 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 ∼0.5–1 Jy rise in the 150-MHz flux density may correspond to sustained flaring activity over a period of approximately 6 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.
Currently, in order to ensure the required fault-proof level of technological processes in agricultural production, the following strategies among the main ones: afterfailure, planned systematic and ...a mixed electrical equipment maintenance and repair strategy. The pervasion of information technology in this segment was not widespread. Application of information technologies in conjunction with implementation of risk-oriented strategy is one of the promising directions of electrical equipment maintenance optimization, yet requires adaptation to sectoral characteristics of agricultural production. The article describes the problem of determining the optimal conditions for adjusting the frequency of maintenance and repair of electrical equipment on the basis of risk-oriented approach. To solve this problem, the equation of annual costs for maintenance and repair of electrical equipment was drawn up taking into account the parameter of its failure risk. The relationship between the change of relative risk and the service frequency was established; based on it, the ranges of frequency adjustment of maintenance and ongoing repair were determined.
The hypersoft state of Cygnus X–3 Koljonen, K. I. I.; Maccarone, T.; McCollough, M. L. ...
Astronomy and astrophysics (Berlin),
04/2018, Letnik:
612
Journal Article
Recenzirano
Context.
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.
Aim.
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, in which 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
γ
-ray emission is observed. We use multiwavelength observations to study the nature of the hypersoft state.
Methods.
We observed Cygnus X–3 during the hypersoft state with
Swift
and
NuSTAR
in 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
.
Results.
We found that the spectra and timing properties of the multiwavelength observations can be explained by a scenario in which 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.
The results of the analysis of 205 brightest sources (
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 taken and the data collected in the CATS astrophysical catalogs database, the radio spectra of the objects were constructed. For a quarter of all detected sources, data at frequencies above 4 GHz were obtained for the first time, and for the rest they were supplemented. The variability of radiation sources on the scales of the year, from days to months, has been 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 of the brightest sources with an average value of
mJy. All sources are identified with objects from optical and infrared catalogs. The radio luminosity was calculated for 112 objects with known redshifts.
The results of the analysis of 205 brightest sources ( 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 taken and the data collected in the CATS astrophysical catalogs database, the radio spectra of the objects were constructed. For a quarter of all detected sources, data at frequencies above 4 GHz were obtained for the first time, and for the rest they were supplemented. The variability of radiation sources on the scales of the year, from days to months, has been studied. The greatest change in the radio flux was found in the blazar B2 132422. The search for daily variability was carried out for 26 of the brightest sources with an average value of mJy. All sources are identified with objects from optical and infrared catalogs. The radio luminosity was calculated for 112 objects with known redshifts.
With frequent flaring activity of its relativistic jets, Cygnus X-3 (Cyg X-3) is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high-energy γ-ray ...emission, thanks to detections by Fermi Large Area Telescope (Fermi/LAT) and AGILE. In 2011, Cyg X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy γ-ray emission. We present the results of a multiwavelength campaign covering a quenched state, when radio emission from Cyg X-3 is at its weakest and the X-ray spectrum is very soft. A giant (∼20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E≥ 100 MeV) reveal renewed γ-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the γ-ray emission is not exclusively related to the rare giant radio flares. A three-week period of γ-ray emission is also detected when Cyg X-3 was weakly flaring in radio, right before transition to the radio quenched state. No γ-rays are observed during the ∼1-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio-quenched) state trigger γ-ray emission, implying a connection to the accretion process, and also that the γ-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.
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