Results 1 - 7 of 7
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[en] We study the complex correlations between optical and X-ray variability in the black hole X-ray nova XTE J1118+480. We find that the optical and X-ray fluctuations of very different shapes, amplitudes and time-scales are correlated in a similar mode where the optical light curve is seemingly related to the time derivative of the X-rays
[en] We report on Cyg X-1 observations performed by the SPI telescope on board the INTEGRAL mission and distributed over more than 6 years. We investigate the variability of the intensity and spectral shape of this peculiar source in the hard X-ray domain, and more particularly up to the MeV region. We first study the total averaged spectrum which presents the best signal-to-noise ratio (4 Ms of data). Then, we refine our results by building mean spectra by periods and gathering those of similar hardness. Several spectral shapes are observed with important changes in the curvature between 20 and 200 keV, even at the same luminosity level. In all cases, the emission decreases sharply above 700 keV, with flux values above 1 MeV (or upper limits) well below the recently reported polarized flux, while compatible with the MeV emission detected some years ago by the Compton Gamma-ray Observatory/COMPTEL. Finally, we take advantage of the spectroscopic capability of the instrument to seek for spectral features in the 500 keV region with negative results for any significant annihilation emission on 2 ks and day timescales, as well as in the total data set.
[en] We study the high-energy emission of the Galactic black hole candidate GX 339-4 using INTEGRAL/SPI and simultaneous RXTE/PCA data. By the end of 2007 January, when it reached its peak luminosity in hard X-rays, the source was in a bright hard state. The SPectrometer on INTEGRAL (SPI) data from this period show a good signal-to-noise ratio, allowing a detailed study of the spectral energy distribution up to several hundred keV. As a main result, we report on the detection of a variable hard spectral feature (≥150 keV) which represents a significant excess with respect to the cutoff power-law shape of the spectrum. The SPI data suggest that the intensity of this feature is positively correlated with the 25-50 keV luminosity of the source and the associated variability timescale is shorter than 7 hr. The simultaneous Proportional Counter Array data, however, show no significant change in the spectral shape, indicating that the source is not undergoing a canonical state transition. We analyzed the broadband spectra in the lights of several physical models, assuming different heating mechanisms and properties of the Comptonizing plasma. For the first time, we performed quantitative model fitting with the new versatile Comptonization code BELM, accounting self-consistently for the presence of a magnetic field. We show that a magnetized medium subject to pure non-thermal electron acceleration provides a framework for a physically consistent interpretation of the observed 4-500 keV emission. Moreover, we find that the spectral variability might be triggered by the variations of only one physical parameter, namely the magnetic field strength. Therefore, it appears that the magnetic field is likely to be a key parameter in the production of the Comptonized hard X-ray emission.
[en] This school, dedicated to young researchers, will clarify our present knowledge of the X-ray sky and give the opportunity to learn about the observatories and tools which are available. The contributions have been organized into 3 issues: -) fundamental physics, -) X-ray and Gamma-ray instruments and analysis techniques, and -) astrophysical objects. This document gathers only the slides of the presentations
[en] We present a new keplerian accretion disc solution, the so-called Jet Emitting Disc (JED hereafter), which is part of global self-consistent disc-jet MHD structure. In our framework, a large scale, organized vertical magnetic field is threading the JED giving birth, when conditions are met, to stationnary self-collimated non relativistic jets. The main condition is that the magnetic pressure Pmag must be of the order of the total pressure Ptot in the JED and a direct consequence is a jet torque largely dominating the viscuous torque. This in turn implies an accretion velocity of the order of the sound speed and then a density much lower than a standard accretion disc. Moreover, most of the accretion power Pacc being extracted by the jet, only part of it (<50%) is liberated in the JED as heating power.
[en] We present the discovery of a reflection-dominated active galactic nucleus (AGN) in the early-type radio-quiet galaxy ESO 565-G019 with Suzaku and Swift/Burst Alert Telescope. The source X-ray spectrum below 10 keV is characteristic of other Compton-thick (CT) AGNs, clearly showing an inverted continuum and prodigious fluorescence iron emission above ∼3 keV. A Compton shoulder to the neutral Fe Kα line also appears to be present. There is evidence for long-term hard X-ray flux variability that we associate with changes in the intrinsic AGN power law. More of such reflection-dominated AGNs should be uncovered in the near future with the increased sensitivity of ongoing and new hard X-ray surveys. ESO 565-G019 is hosted in an early-type galaxy whose morphology has been variously classified as either type E or type S0. Only about 20 bona fide CT-AGNs have been identified in the local universe so far, and all exist in host galaxies with late Hubble types (S0 or later). CT columns of nuclear obscuring gas are uncommon in early-type galaxies in the local universe, so confirmation of the exact morphological class of ESO 565-G019 is important. Infrared photometry also shows the presence of large quantities of cool dust in the host, indicative of significant ongoing star formation. ESO 565-G019 may be the first identified local example of minor-merger-driven CT-AGN growth in an early-type host, or may be the result of interaction with its neighboring galaxy ESO 565-G018 in a wide pair
[en] Many X-ray binaries remain undetected in the mid-infrared, a regime where emission from their compact jets is likely to dominate. Here, we report the detection of the black hole binary GX 339-4 with the Wide-field Infrared Survey Explorer (WISE) during a very bright, hard accretion state in 2010. Combined with a rich contemporaneous multiwavelength data set, clear spectral curvature is found in the infrared, associated with the peak flux density expected from the compact jet. An optically thin slope of ∼ -0.7 and a jet radiative power of >6 x 1035 erg s-1 (d/8 kpc)2 are measured. A ∼24 hr WISE light curve shows dramatic variations in mid-infrared spectral slope on timescales at least as short as the satellite orbital period ∼95 minutes. There is also significant change during one pair of observations spaced by only 11 s. These variations imply that the spectral break associated with the transition from self-absorbed to optically thin jet synchrotron radiation must be varying across the full wavelength range of ∼3-22 μm that WISE is sensitive to, and more. Based on four-band simultaneous mid-infrared detections, the break is constrained to frequencies of ∼4.6+3.5-2.0 x 1013 Hz in at least two epochs of observation, consistent with a magnetic field B ∼ 1.5(± 0.8) x 104 G assuming a single-zone synchrotron emission region. The observed variability implies that either B or the size of the acceleration zone above the jet base is being modulated by factors of ∼10 on relatively short timescales.