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Register a new userINTEGRAL discovery of a high-energy tail in the microquasar Cygnus X-3
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The X-ray spectra of X-ray binaries are dominated by emission of either soft or hard X-rays which defines their soft and hard spectral states. Cygnus X-3 is amongst the list of X-ray binaries that show quite complex behavior, with various distinct spectral states. Because of its softness and intrinsic low flux above typically 50 keV, very little is known about the hard X/soft gamma-ray (100-1000 keV) emission in Cygnus X-3. Using the whole INTEGRAL data base, we aim to explore the 3-1000 keV spectra of Cygnus X-3. This allows to probe this region with the highest sensitivity ever, and search for the potential signature of a high-energy non-thermal component as sometimes seen in other sources. Our work is based on state classification carried out in previous studies with data from the Rossi X-Ray Timing Explorer. We extend this classification to the whole INTEGRAL data set and perform a long-term state-resolved spectral analysis. Six stacked spectra were obtained using 16 years of data from JEM-X, ISGRI, and SPI. We extract stacked images in three different energy bands, and detect the source up to 200 keV. In the hardest states, our phenomenological approach reveals the presence of an component > 50 keV in addition to the component usually interpreted as thermal Comptonization. We apply a more physical model of hybrid thermal/nonthermal corona to characterize this component and compare our results with those of previous studies. Our modeling indicates a more efficient acceleration of electrons in states where major ejections are observed. We find a dependence of the photon index of the power law as a function of the strong orbital modulation of the source in the Flaring InterMediate (FIM) state. This dependence could be due to a higher absorption when Cygnus X-3 is behind its companion. However, the uncertainties on the density column prevent us from drawing conclusions.
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The study of relativistic particle acceleration is a major topic of high-energy astrophysics. It is well known that massive black holes in active galaxies can release a substantial fraction of their accretion power into energetic particles, producing gamma-rays and relativistic jets. Galactic microquasars (hosting a compact star of 1-10 solar masses which accretes matter from a binary companion) also produce relativistic jets. However, no direct evidence of particle acceleration above GeV energies has ever been obtained in microquasar ejections, leaving open the issue of the occurrence and timing of extreme matter energization during jet formation. Here we report the detection of transient gamma-ray emission above 100 MeV from the microquasar Cygnus X-3, an exceptional X-ray binary which sporadically produces powerful radio jets. Four gamma-ray flares (each lasting 1-2 days) were detected by the AGILE satellite simultaneously with special spectral states of Cygnus X-3 during the period mid-2007/mid-2009. Our observations show that very efficient particle acceleration and gamma-ray propagation out of the inner disk of a microquasar usually occur a few days before major relativistic jet ejections. Flaring particle energies can be thousands of times larger than previously detected maximum values (with Lorentz factors of 105 and 102 for electrons and protons, respectively). We show that the transitional nature of gamma-ray flares and particle acceleration above GeV energies in Cygnus X-3 is clearly linked to special radio/X-ray states preceding strong radio flares. Thus gamma-rays provide unique insight into the nature of physical processes in microquasars.
0.1-10 MeV observations of the black hole microquasar Cygnus X-1 have shown the presence of a spectral feature in the form of a power law in addition to the standard black body and Comptonization components observed by INTEGRAL. This so-called high-energy tail has recently been shown to be strong in its hard spectral state and interpreted as high-energy part of the emission from a compact jet. This result was, however, obtained from a data set dominated by hard state observations. In the soft state, only upper limits on the presence and hence the potential parameters of a high-energy tail could be derived. Using an extended data set we aim at obtaining better constraints on the properties of this spectral component in both states. We make use of data obtained from 15 years of observations with the INTEGRAL satellite. The data set is separated into the different states and we analyse stacked state-resolved spectra obtained from the X-ray monitors, the gamma-ray imager, and the gamma-ray spectrometer onboard. A high-energy component is detected in both states confirming its earlier detection in the hard state and its suspected presence in the soft state with INTEGRAL. We first characterize the high-energy tail components in the two states through a model-independent, phenomenological analysis. We then apply physical models based on hybrid Comptonization. The spectra are well modeled in all cases, with a similar goodness of the fits. While in the phenomenological approach the high-enery tail has similar indices in both states, the fits with the physical models seem to indicate different properties. We discuss the potential origins of the high-energy components in both states, and favor an interpretation where the part of the high-energy component is due to a compact jet in the hard state and hybrid Comptonization in either a magnetised or non-magnetised corona in the soft state.
We report results from TeV gamma-ray observations of the microquasar Cygnus X-3. The observations were made with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) over a time period from 2007 June 11 to 2011 November 28. VERITAS is most sensitive to gamma rays at energies between 85 GeV to 30 TeV. The effective exposure time amounts to a total of about 44 hours, with the observations covering six distinct radio/X-ray states of the object. No significant TeV gamma-ray emission was detected in any of the states, nor with all observations combined. The lack of a positive signal, especially in the states where GeV gamma rays were detected, places constraints on TeV gamma-ray production in Cygnus X-3. We discuss the implications of the results.
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.
We present the analysis of an extended textit{INTEGRAL} dataset of the high-mass microquasar Cygnus X-1. We first classify, in a model-independent way, all the textit{INTEGRAL} individual pointings taken between 2003 and 2016 in three basic spectral states. This, in particular, allows us to triple the exposure time of the soft state in comparison with previous publication. We then study the spectral properties of the 5--400 keV stacked spectra of the soft and hard states and provide the parameters obtained with our modelling. Using a refined alternative method of extracting the Compton double events of the IBIS telescope, we then extract high-energy ($>$400 keV) spectra in the two states. We do detect an hard tail in both states. Our refined analysis allows us to obtain a hard state (count) spectrum at a flux lower than previously published by our team. Although a full estimate of the calibration property of this improved software is still needed, this seems to be more inline with the hard state hard tail seen with other instruments.
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