Cygnus X-1 is a Galactic black-hole binary and a microquasar. Its X-ray emission originates most likely in the accretion flow, while the radio emission is from a magnetized jet. We study long-term cross-correlations between its X-ray and radio fluxes, searching for lags of the peak of the correlation. We use soft X-ray data from the All Sky Monitor on board of Rossi X-ray Timing Explorer, hard X-ray data from the Burst Alert Telescope on board of Neil Gehrels Swift, and 15 GHz radio monitoring data from the Ryle and AMI telescopes, which light curves cover all of the spectral states of Cyg X-1. Previous studies of radio/X-ray correlations in black-hole binaries concentrated on the soft X-ray/radio correlation in the hard spectral state. In contrast, our strongest correlation is between the hard X-rays and radio in the entire data at a $\lesssim 1$-day lag. This indicates the jet formation from a hard X-ray emitting corona/hot accretion flow through all states of Cyg X-1. We also find evidence for a long lag of the radio with respect to the soft X-rays in the soft state. This indicates long-term advection of the magnetic field through the accretion disc from its high-mass donor, which is similar to the case of another microquasar with a high-mass donor, Cyg X-3.
We present the first X-ray reverberation mass measurement of a stellar-mass black hole. Accreting stellar-mass and supermassive black holes display characteristic spectral features resulting from reprocessing of hard X-rays by the accretion disc, such as an Fe K$α$ line and a Compton hump. This emission probes of the innermost region of the accretion disc through general relativistic distortions to the line profile. However, these spectral distortions are insensitive to black hole mass, since they depend on disc geometry in units of gravitational radii. Measuring the reverberation lag resultin…
Cygnus X-3 is a unique microquasar. Its X-ray emission shows a very strong 4.8-hour orbital modulation. But its mass-donating companion is a Wolf-Rayet star. Also unlike most other X-ray binaries Cygnus X-3 is relatively bright in the radio virtually all of the time (the exceptions being the quenched states). Cygnus X-3 also undergoes giant radio outbursts (up to 20 Jy). In this presentation we discuss and review the flaring behavior of Cygnus X-3 and its various radio/X-ray states. We present a revised set of radio/X-ray states based on Cygnus X-3's hardness-intensity diagram (HID). We also e…
Some OB stars show variable non-thermal radio emission. The non-thermal emission is due to synchrotron radiation that is emitted by electrons accelerated to high energies. The electron acceleration occurs at strong shocks created by the collision of radiatively-driven stellar winds in binary systems. Here we present results of our modelling of two colliding wind systems: Cyg OB2 No. 8A and Cyg OB2 No. 9.
We investigate the complex behavior of energy- and frequency-dependent time/phase lags in the plateau state and the radio-quiet hard state of GRS 1915+105. In our timing analysis, we find that when the source is faint in the radio, QPOs are observed above 2 Hz and typically exhibit soft lags (soft photons lag hard photons), whereas QPOs in the radio-bright plateau state are found below 2.2 Hz and consistently show hard lags. The phase lag at the QPO frequency is strongly anti-correlated with the QPO frequency, changing sign at 2.2 Hz. However, the phase lag at the frequency of the first harmon…
Using a cross-correlation method, we study the X-ray halo of Cyg X-3. Two components of dust distributions are needed to explain the time lags derived by the cross-correlation method. Assuming the distance as 1.7 kpc for Cygnus OB2 association (a richest OB association in the local Galaxy) and another uniform dust distribution, we get a distance of $7.2^{+0.3}_{-0.5}$ kpc (68$%$ confidence level) for Cyg X-3. When using the distance estimation of Cygnus OB2 as 1.38 kpc or 1.82 kpc, the inferred distance for Cyg X-3 is $3.4^{+0.2}_{-0.2}$ kpc or $9.3^{+0.6}_{-0.4}$ kpc respectively. The distanc…
Accreting black hole sources show a wide variety of rapid time variability, including the manifestation of time lags during X-ray transients, in which a delay (phase shift) is observed between the Fourier components of the hard and soft spectra. Despite a large body of observational evidence for time lags, no fundamental physical explanation for the origin of this phenomenon has been presented. We develop a new theoretical model for the production of X-ray time lags based on an exact analytical solution for the Fourier transform describing the diffusion and Comptonization of seed photons propa…
We study the radio/X-ray correlation in Cyg X-3. It has been known that the soft and hard X-ray fluxes in the hard spectral state are correlated positively and negatively, respectively, with the radio flux. We show that this implies that the observed $\sim$1--100 keV flux (which is a fair approximation to the bolometric flux) is completely uncorrelated with the radio flux. We can recover a positive correlation (seen in other sources and expected theoretically) if the soft X-rays are strongly absorbed by a local medium. Then, however, the intrinsic X-ray spectrum of Cyg X-3 in its hard state be…
In 2015, a radio transient named Cygnus A-2 was discovered in Cygnus A with the Very Large Array. Because of its radio brightness ($νF_ν \approx 6 \times 10^{39}$ erg s$^{-1}$), this transient likely represents a secondary black hole in orbit around the AGN. Using {\it Chandra} ACIS observations from 2015 to 2017, we have looked for an X-ray counterpart to Cygnus A-2. The separation of 0.42 arcsec means that Cygnus A-2 can not be spatially resolved, but by comparing the data with simulated \texttt{marx} data, we put an upper limit to the 2-10 keV X-ray luminosity of Cygnus A-2 of $1 \times 10^…
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 constr…
In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cyg X-3, we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival VLBA data at 5 or 15 GHz and new e-EVN data at 5 GHz. We also present 5 GHz MERLIN observations of an outburst of Cyg X-3. In the X-ray regime we use quasi-simultaneous with radio, monitoring and pointed RXTE observations. We find that when the radio emission from both jet and core is globally considered, the beha…
Radio-X-ray Time Lags in GX 339-4: Probing Magnetic Field Transport in Black Hole Accretion
Institute for Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Department of Astronomy, School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院天文学系）；Shanghai Astronomical Observatory, Chinese Academy of Sciences (CAS)（中国科学院上海天文台）
Many accreting black holes manifest time lags during outbursts, in which the hard Fourier component typically lags behind the soft component. Despite decades of observations of this phenomenon, the underlying physical explanation for the time lags has remained elusive, although there are suggestions that Compton reverberation plays an important role. However, the lack of analytical solutions has hindered the interpretation of the available data. In this paper, we investigate the generation of X-ray time lags in Compton scattering coronae using a new mathematical approach based on analysis of t…
Compelling evidence of a link between the lags of the quasi-periodic oscillations and the radio jet in the black-hole X-ray binary GRS 1915+105
Instituto Argentino de Radioastronomía (CCT La Plata, CONICET（阿根廷射电天文研究所）；CICPBA（拉普拉塔国立大学天文与地球物理学院）；UNLP)（格罗宁根大学卡普坦天文研究所）；Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata（意大利国家天体物理研究所布雷拉天文台）；Kapteyn Astronomical Institute, University of Groningen（中国科学院高能物理研究所粒子天体物理重点实验室）；Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera（牛津大学物理系天体物理学）；Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences；Astrophysics, Department of Physics, University of Oxford
Using all the observations from Rossi X-ray Timing Explorer for accreting neutron star XTE J1701-462, we carry out a systematic study on the cross-correlation between its soft and hard light curves. The anti-correlations appear at the hard vertex and on the upper normal branch (NB) in the Cyg-like interval, occur on the horizontal branch (HB) and/or upper NB in the first and second Sco-like intervals, and display at the upper flaring branch (FB) in the third Sco-like interval. We suggest that the anti-correlation might evolve with luminosity, because with decreasing of luminosity, the source e…
In this work we combine SEDs, radio maps and polarization observations to understand the emission mechanisms in Cygnus X-1. Our radiative model indicates that the MeV emission originates in the jet and that all the very high-energy emission is from hadronic origin. We also performed a synthetic radio map that suggests that our description of the magnetic field should be improved, since it leads to a very compact emission region. In order to choose the most suitable magnetic field geometry, we investigated the polarization in X-rays and we found that very simple geometries can explain the high …
Gamma Cygni is a young supernova remnant located in the Cygnus region. MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes detected TeV emission (MAGIC J2019+408) to the north-west of this remnant, about 5 arcmin from its border. We want to identify the radio sources within the region encompassing gamma Cygni and MAGIC J2019+408 to shed light on their nature and investigate if these radio sources could be potential contributors to gamma-ray emission. We carried out a detailed study of the data we obtained with a survey of the Cygnus region at 325 and 610 MHz with the Giant Metrewave R…
We present simultaneous multi-band radio and X-ray observations of the black hole X-ray binary Cygnus X-1, taken with the Karl G. Jansky Very Large Array and the Nuclear Spectroscopic Telescope Array. With these data, we detect clear flux variability consistent with emission from a variable compact jet. To probe how the variability signal propagates down the jet flow, we perform detailed timing analyses of our data. We find that the radio jet emission shows no significant power at Fourier frequencies $f\gtrsim0.03$ Hz (below $\sim30$ sec timescales), and that the higher frequency radio bands (…
Recent analyses of the broad spectral energy distributions (SED) of extensive lobes of local radio-galaxies have confirmed the leptonic origin of their Fermi/LAT gamma-ray emission, significantly constraining the level of hadronic contribution. SED of distant (D > 125 Mpc) radio-galaxy lobes are currently limited to the radio and X-ray bands, hence give no information on the presence of non-thermal (NT) protons but are adequate to describe the properties of NT electrons. Modeling lobe radio and X-ray emission in 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236, we fully determine the prop…
We study free-free absorption of radio emission by winds of massive stars. We derive formulae for the optical depth through the wind measured from a point of emission along a jet, taking into account Compton and photoionization heating and Compton, recombination, line and advection cooling. We apply the developed formalism to radio monitoring data for Cyg X-1, which allows us to obtain strong constraints on the structure of its inner jet. With the data at 15 GHz, and taking into account an anisotropy of the stellar wind in Cyg X-1, we estimate the location of the peak of that emission along th…
With frequent flaring activity of its relativistic jets, Cygnus X-3 is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy Gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cygnus X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy Gamma-ray emission. We present the results of a multi-wavelength campaign covering a quenched state, when radio emission from Cygnus X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~ 20 Jy) optically thin radio flare ma…
We report results from a Giant Metrewave Radio Telescope (GMRT) monitoring campaign on the black hole X-ray binary V404 Cygni during its 2015 June outburst. The GMRT observations were carried out at observing frequencies of 1280, 610, 325 and 235 MHz, and extended from June 26.89 UT (a day after the strongest radio/X-ray outburst) to July 12.93 UT. We find the low-frequency radio emission of V404 Cygni to be extremely bright and fast-decaying in the outburst phase, with an inverted spectrum below 1.5 GHz and an intermediate X-ray state. The radio emission settles to a weak, quiescent state $\a…
We present the long term, frequency-dependent, X-ray time lags of the Seyfert galaxy NGC 4051. We used Rossi X-ray Timing Explorer light curves in the 2-4, 4-7 and 7-10 keV bands and we measured the time-lags at $10^{-7}-10^{-6}$ Hz. This is the lowest frequency range that AGN time-lags have ever been measured. The variations in the higher energy bands are delayed with respect to the variations we observe at 2-4 keV, in agreement with the time-lags at high frequencies. When we combine our results with those from the model fitting of the time lags at higher frequencies we find that that the X-r…
We study long-term radio/X-ray correlations in Cyg X-1. We find the persistent existence of a compact radio jet in its soft state. This represents a new phenomenon in black-hole binaries, in addition to compact jets in the hard state and episodic ejections of ballistic blobs in the intermediate state. While the radio emission in the hard state is strongly correlated with both the soft and hard X-rays, the radio flux in the soft state is not directly correlated with the flux of the dominant disk blackbody in soft X-rays, but instead it is lagged by about a hundred days. We interpret the lag as …
AGILE data on Cygnus X-3 are reviewed focussing on the correlation between the production of gamma-ray transient emission and spectral state changes of the source. AGILE clearly establishes a relation between enhanced gamma-ray emission and the "quenched" radio/hard X-ray states that precede in general major radio flares. We briefly discuss the theoretical implications of our findings.
The view of the gamma-ray universe is being continuously expanded by space high energy (HE) and ground based very-high energy (VHE) observatories. Yet, the angular resolution limitation still precludes a straightforward identification of these gamma-ray emitting sources. Radio observations are an effective tool for searching their possible counterparts at lower energies because the same population of relativistic electrons responsible for radio emission can also produce HE/VHE emission via inverse-Compton scattering. The Cygnus region is crowded by many gamma-ray sources, most of them remainin…
Owing to the frequency and reproducibility of its outbursts, the black-hole candidate GX 339-4 has become the standard against which the outbursts of other black-hole candidate are matched up. Here we present the first systematic study of the evolution of the X-ray lags of the broad-band variability component (0.008-5 Hz) in GX 339-4 as a function of the position of the source in the hardness-intensity diagram. The hard photons always lag the soft ones, consistent with previous results. In the low-hard state the lags correlate with X-ray intensity, and as the source starts the transition to th…
Cygnus X-3 (Cyg X-3) is a well-known microquasar with relativistic jets. Cyg X-3 is especially famous for its giant radio outbursts, which have been observed once every few years since their first discovery. Each giant outburst presumably consists of a series of short-duration flares. The physical parameters of the flares in the giant outbursts are difficult to derive because the successive flares overlap. Here, we report isolated flares in the quiescent phase of Cyg X-3, as observed at 23, 43, and 86 GHz with the 45-m radio telescope at Nobeyama Radio Observatory. The observed flares have sma…
Accreting white dwarfs in binary systems known as cataclysmic variables (CVs) have in recent years been shown to produce radio flares during outbursts, qualitatively similar to those observed from neutron star and black hole X-ray binaries, but their ubiquity and energetic significance for the accretion flow has remained uncertain. We present new radio observations of the CV SS Cyg with Arcminute Microkelvin Imager Large Array, which show for the second time late-ouburst radio flaring, in April 2016. This flaring occurs during the optical flux decay phase, about ten days after the well-establi…
We present the results of our intensive radio observing campaign of the dwarf nova SS Cyg during its 2010 April outburst. We argue that the observed radio emission was produced by synchrotron emission from a transient radio jet. Comparing the radio light curves from previous and subsequent outbursts of this system (including high-resolution observations from outbursts in 2011 and 2012) shows that the typical long and short outbursts of this system exhibit reproducible radio outbursts that do not vary significantly between outbursts, which is consistent with the similarity of the observed optic…
We present X-ray spectral and timing behavior of Cyg X-3 as observed by AstroSat during the onset of a giant radio flare on 01-02 April 2017. Within a time-scale of few hours, the source shows a transition from the hypersoft state (HPS) to a more luminous state (we termed as the very high state) which coincides with the time of the steep rise in radio flux density by an order of magnitude. Modeling the SXT and LAXPC spectra jointly in 0.5-70.0 keV, we found that the first few hours of the observation is dominated by the HPS with no significant counts above 17 keV. Later, an additional flat pow…
To account for the non-thermal emission from the classical nova V2491 Cygni, we perform a series of numerical calculations of radiative transfer of γ-ray photons from the radioactive isotope $^{22}$Na in the matter ejected from a white dwarf. Using a simple wind model for the dynamical evolution of the ejecta and a monte-carlo code, we calculate radiative transfer of the γ-ray photons in the ejecta. Repeated scattering of the γ-ray photons by electrons in the ejecta, i.e., Compton degradation, results in an extremely flat spectrum in the hard X-ray range, which successfully reproduces the obse…
The ejection of a relativistic jet has been observed in the luminous Galactic low mass X-ray binary Cygnus X-2. Using high resolution radio observations, a directly resolved ejection event has been discovered while the source was on the Horizontal Branch of the Z-track. Contemporaneous radio and X-ray observations were made with the European VLBI Network at 6 cm and the Swift X-ray observatory in the 0.3 - 10 keV band. This has been difficult to achieve because of the previous inability to predict jet formation. Two sets of ~10 hr observations were spaced 12 hr apart, the jet apparently switch…
We report on simultaneous optical and X-ray observations of the dwarf nova SS Cyg with Tomo-e Gozen/1.05 m Kiso Schmidt and Neutron star Interior Composition ExploreR (it NICER) / International Space Station (ISS). A total of four observations were carried out in the quiescent state and highly correlated light variations between the two wavelengths were detected. We have extracted local brightness peaks in the light curves with a binning interval of 1 sec, called `shots', and have evaluated time lags between the optical and X-ray variations by using a cross-correlation function. Some shots exh…
The powerful FR II radio galaxy Cygnus A exhibits primary and secondary hotspots in each lobe. A 2 Msec Chandra X-ray image of Cygnus A has revealed an approximately circular hole, with a radius of 3.9 kpc, centered on the primary hotspot in the eastern radio lobe, hotspot E. We infer the distribution of X-ray emission on our line-of-sight from an X-ray surface brightness profile of the radio lobe adjacent to the hole and use it to argue that the hole is excavated from the radio lobe. The surface brightness profile of the hole implies a depth at least 1.7 $\pm$ 0.3 times greater than its proje…
We have studied the X-ray variability patterns and correlations of the radio and X-ray fluxes in all spectral states of Cyg X-1 using X-ray data from RXTE/ASM, CGRO/BATSE, and Swift/BAT. In the hard state, the dominant spectral variability is a changing of normalisation with fixed spectral shape, while in the intermediate state the slope changes, with a pivot point around 10 keV. In the soft state, the low energy X-ray emission dominates the bolometric flux which is only loosely correlated with the high energy emission. In black hole binaries in the hard state, the radio flux is generally foun…
We study high-energy $γ$-rays observed from Cyg X-3 by the Fermi Large Area Telescope and the 15-GHz emission observed by the Ryle Telescope and the Arcminute Microkelvin Imager. We measure the $γ$-ray spectrum averaged over strong flares much more accurately than before, and find it well modelled by Compton scattering of stellar radiation by relativistic electrons with the power law index of $\simeq$3.5 and a low-energy cutoff at the Lorentz factor of $\sim\!10^3$. We find a weaker spectrum in the soft spectral state, but only upper limits in the hard and intermediate states. We measure stron…
The abundance of accelerators and the ambient conditions make Cygnus X a natural laboratory for studying the life cycle of cosmic-rays (CRs). This naturally makes the Cygnus X complex a highly interesting source in neutrino astronomy, in particular concerning a possible detection with the IceCube Neutrino Observatory, which has a good view of the northern hemisphere. In this paper, we model the multiwavelength spectrum of the Cygnus, for the first time using a broad data set from radio, MeV (COMPTEL), GeV (Fermi), TeV (Argo) and 10s of TeV (Milagro) energies. The modeling is performed assuming…
We analyse in detail the X-ray data of the microquasar Cygnus X-3 obtained during major radio flaring episodes in 2006 with multiple observatories. The analysis consists of two parts: probing the fast (~ 1 minute) X-ray spectral evolution with Principal Component Analysis followed by subsequent spectral fits to the time-averaged spectra (~ 3 ks). Based on the analysis we find that the overall X-ray variability during major flaring episodes can be attributed to two principal components whose evolution based on spectral fits is best reproduced by a hybrid Comptonization component and a bremsstra…
State-Dependent X-ray Variability in Cygnus X-1: A 12-Year NuSTAR Timing Study of Accretion Flow Geometry
Boston University（波士顿大学）；Raman Research Institute（拉曼研究所）；Indian Institute of Science Education and Research Bhopal（印度科学教育与研究学院博帕尔分校）；Florida International University（佛罗里达国际大学）；Miami Dade College（迈阿密戴德学院）；Osmania University（奥斯曼尼亚大学）；Physical Research Laboratory（物理研究实验室）；UN Center for Space Science and Technology Education in Asia and Pacific (CSSTEAP)（联合国亚洲及太平洋空间技术和外空活动教育训练中心）；Sardar Vallabhbhai National Institute of Technology, Surat（萨达尔·瓦拉巴伊国立技术学院苏拉特分校）；Pondicherry University（本地治里大学）；School of Sciences, JAIN (Deemed-to-be University), Bengaluru（JAIN（视为大学）班加罗尔理学院）；Janusz Gil Institute of Astronomy, University of Zielona Góra（绿山大学扬努什·吉尔天文学研究所）
Polarization of the >~400 keV hard tail of the microquasar Cygnus X-1 has been independently reported by INTEGRAL/IBIS, and INTEGRAL/SPI and interpreted as emission from a compact jet. These conclusions were, however, based on the accumulation of all INTEGRAL data regardless of the spectral state. We utilize additional INTEGRAL exposure accumulated until December 2012, and include the AMI/Ryle (15 GHz) radio data in our study. We separate the observations into hard, soft, and intermediate/transitional states and detect radio emission from a compact jet in hard and intermediate states, but not …
Cygnus A, the nearest truly powerful radio galaxy, resides at the centre of a massive galaxy cluster. Chandra X-ray observations reveal its cocoon shocks, radio lobe cavities and an X-ray jet, which are discussed here. It is argued that X-ray emission from the outer regions of the cocoon shocks is nonthermal. The X-ray jets are best interpreted as synchrotron emission, suggesting that they, rather than the radio jets, are the path of energy flow from the nucleus to the hotspots. In that case, a model shows that the jet flow is non-relativistic and carries in excess of one solar mass per year.
We have analyzed archival VLBA data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by \citet{per18} approximately 0.4\arcsec~ from the nucleus of Cygnus A (Cyg A-2). \citet{per18} use VLA and VLBA archival data (between 1989 and 1997) to show that the transient rises in flux density by a factor of at least five in less than approximately 20 years. With the additional data presented here, we revise the rise time to between approximately four years and six years, based on a new detection of the source at 15.4 GHz from October 2011. Our resu…
X-ray and radio data recently acquired as part of a project to study Cyg OB2#9 are used to constrain physical models of the binary system, providing in-depth knowledge about the wind-wind collision and the thermal, and non-thermal, emission arising from the shocks. We use a three-dimensional, adaptive mesh refinement simulation (including wind acceleration, radiative cooling, and the orbital motion of the stars) to model the gas dynamics of the wind-wind collision. The simulation output is used as the basis for radiative transfer calculations considering the thermal X-ray emission and the ther…
The microquasar Cygnus X-3 underwent a giant radio flare in April 2017, reaching a maximum flux of $\sim 16.5$ Jy at 8.5 GHz. We present results from a long monitoring campaign carried out with Medicina at 8.5, 18.6 and 24.1 GHz, in parallel to the Metsähovi radio telescope at 37 GHz, from 4 to 11 April 2017. We observe a spectral steepening from $α= 0.2$ to 0.5 (with $S_ν \propto ν^{-α}$) within 6 h around the epoch of the peak maximum of the flare, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux d…
We present results from multi-wavelength simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cyg in quiescence. Our coverage with NuSTAR provides the very first opportunity to study the X-ray spectrum of V404 Cyg at energies above 10 keV. The unabsorbed broad-band (0.3--30 keV) quiescent luminosity of the source is 8.9$\times$10$^{32}$ erg s$^{-1}$ for a distance of 2.4 kpc. The source shows clear variability on short time scales (an hour to a couple of hours) in radio, soft X-ray and hard X-ray bands in the form of multiple flares. The broad-band X-ray spectra obtain…
Cygnus A harbours the nearest powerful radio jet of an Fanaroff-Riley (FR) class II radio galaxy in a galaxy cluster where the interaction of the jet with the intracluster medium (ICM) can be studied in detail. We use a large set of Chandra archival data, VLA and new LOFAR observations to shed new light on the interaction of the jets with the ICM. We identify an X-ray cavity in the distribution of the X-ray emitting plasma in the region south of the Cyg A nucleus which has lower pressure than the surrounding medium. The LOFAR and VLA radio observations show that the cavity is filled with synch…
We have re-analyzed archival RXTE data of the X-ray binary Cygnus X-3 with a view to investigate the timing properties of the source. As compared to previous studies, we use an extensive sample of observations that include all the radio/X-ray spectral states that have been categorized in the source recently. In this study we identify two additional instances of Quasi-Periodic Oscillations that have centroid frequencies in the mHz regime. These events are all associated to a certain extent with major radio flaring, that in turn is associated with relativistic jet ejection events. We review brie…
We have performed a principal component analysis on the X-ray spectra of the microquasar Cygnus X-3 from RXTE, INTEGRAL and Swift during a major flare ejection event in 2006 May-July. The analysis showed that there are two main variability components in play, i.e. two principal components explained almost all the variability in the X-ray lightcurves. According to the spectral shape of these components and spectral fits to the original data, the most probable emission components corresponding to the principal components are inverse-Compton scattering and bremsstrahlung. We find that these compo…
We present simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cygni at the end of its 2015 outburst. From 2015 July 11-August 5 we monitored V404 Cygni with Chandra, Swift, and NuSTAR in the X-ray, and with the Karl G. Jansky Very Large Array and the Very Long Baseline Array in the radio, spanning a range of luminosities that were poorly covered during its previous outburst in 1989 (our 2015 campaign covers 2e33<Lx<1e34 erg/s). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Gamma~1.6 (at Lx~1e34 erg/s) to a softer Gamma~2 (at…
We present a timing analysis of threeRossi X-ray Timing Explorer observations of the black hole binary Cygnus X-1 with the propagating mass accretion rate fluctuations model PROPFLUC. The model simultaneously predicts power spectra, time lags, and coherence of the variability as a function of energy. The observations cover the soft and the hard state of the source, and the transition between the two. We find good agreement between model pre-dictions and data in the hard and in the soft state. Our analysis suggests that in the soft state the fluctuations propagate in an optically thin hot flow …
Cosmic rays, thermal gas and magnetic fields in FRII radio cavities are assumed to come entirely from winds flowing from just behind the jet shocks. Combining analytic and computational methods, it is shown that the computed radio-electron energy distribution and synchrotron emissivity spectra everywhere in the Cygnus A radio cavity agrees with radio observations of the Cygnus A lobes. The magnetic field energy density is small everywhere and evolves passively in the post-shock wind. Most synchrotron emission arises in recent post-shock material as it flows back along the radio cavity wall. Be…
In 2009, Cygnus X-3 (Cyg X-3) became the first microquasar to be detected in the GeV γ-ray regime, via the satellites Fermi and AGILE. The addition of this new band to the observational toolbox holds promise for building a more detailed understanding of the relativistic jets of this and other systems. We present a rich dataset of radio, hard and soft X-ray, and γ-ray observations of Cyg X-3 made during a flaring episode in 2010 May. We detect a ~3-d softening and recovery of the X-ray emission, followed almost immediately by a ~1-Jy radio flare at 15 GHz, followed by a 4.3σ γ-ray flare (E > 10…
We present a multiwavelength study of the black hole X-ray binary V404 Cyg in quiescence, focusing upon the spectral energy distribution (SED). Radio, optical, UV, and X-ray coverage is simultaneous. We supplement the SED with additional non-simultaneous data in the optical through infrared where necessary. The compiled SED is the most complete available for this, the X-ray and radio brightest quiescent black hole system. We find no need for a substantial contribution from accretion light from the near-UV to the near-IR, and in particular the weak UV emission constrains published spectral mode…
Cygnus X-3 (Cyg X-3) is a well-known microquasar producing variable emission at all wavelengths. Cyg X-3 is a prominent X-ray binary producing relativistic jets, and studying its high energy emission is crucial for the understanding of the fundamental acceleration processes in accreting compact objects. Aims. Our goal is to study extreme particle acceleration and γ-ray production above 100 MeV during special spectral states of Cyg X- 3 usually characterized by a low hard X-ray flux and enhanced soft X-ray states. We observed Cyg X-3 with the AGILE satellite in extended time intervals from 2009…
In this contribution we model the non-thermal emission (from radio to gamma-rays) produced in the compact (and recently detected) colliding wind region in the multiple stellar system Cyg OB2 #5. We focus our study on the detectability of the produced gamma-rays.
We present a serendipitous multiwavelength campaign of optical photometry simultaneous with Integral X-ray monitoring of the 2015 outburst of the black hole V404 Cyg. Large amplitude optical variability is generally correlated with X-rays, with lags of order a minute or less compatible with binary light travel timescales or jet ejections. Rapid optical flaring on time-scales of seconds or less is incompatible with binary light-travel timescales and has instead been associated with synchrotron emission from a jet. Both this rapid jet response and the lagged and smeared one can be present simult…
