Results 1 - 10 of 24
Results 1 - 10 of 24. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] Observations of jets from stellar-mass sources located in our Galaxy offer a unique opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of the dynamics and energetics of relativistic jets from Galactic x-ray binaries and active galactic nuclei. We review recent observations of X-ray jets from Galactic black hole candidates. Spatially resolved X-ray spectra from SS 433 have provided evidence for re-heating in a hadronic jet and may offer an observational probe of jet collimation. A large-scale jet from the now quiescent transient 4U 1755-33 appears to indicate continual jet formation over a period of 10-30 years. Detection of a jet from XTE J1550-564 has provided the first direct measurement of gradual deceleration of a jet from a black hole and strong evidence for the re-energization of jet particles to energies up to 10 TeV at sites far from the jet origin
[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] This review presents the stereolithography fabrication of epoxy and acrylate syntactic foams based on hollow glass microspheres. Physicochemical analysis has been performed on the fabricated 3D syntactic foam items containing different amounts of microspheres. The surface free energies, light transmittance, density of the syntactic foams were investigated. Criteria for the choice of a polymeric binder are discussed.
[en] GX 339-4 has been one of the key sources for unravelling the accretion ejection coupling in accreting stellar mass black holes. After a long period of quiescence between 1999 and 2002, GX 339-4 underwent a series of 4 outbursts that have been intensively observed by many ground based observatories (radio/infrared/optical) and satellites (X-rays). Here, we present some specific results of these broad band observational campaigns, focusing on the optical-infrared/X-ray flux correlations over the four outbursts. Thanks to our extensive data-set, we found a strong OIR/X-ray correlation over four decades with the presence of a break in the correlation index. These results seem to favour a synchrotron self-Compton origin for the X-ray emission in GX 339-4 during the hard state and could also provide an indirect detection of the break frequency in the synchrotron spectrum of the compact jets.
[en] A new process called ''Laser Induced Paste Agglomeration'' (LIPA) is being developed for the direct manufacture of tooling and functional prototypes from the data computed by a CAD software. The paste is composed of a powdered material and a liquid binder. The process consists in depositing a thin layer of paste then in solidifying a part of it by a laser beam. The 3D object is then manufactured layer by layer. Many materials, such as polymers, metals and ceramics, can be used to manufacture parts by this process. This paper mainly describes the agglomeration of ceramic paste, which is composed of alumina powder and a silicate binder. The parts made of ceramic manufactured by this technique are porous. After sintering at 800 C, the strength of four-point bending tests on the samples (10.6 - 17.3 MPa) is comparable with some other similar processes (10 - 18.7 MPa). The phase transformations during the agglomeration and the sintering are also discussed. (orig.)
[en] 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, we observed Cyg X-3 in order 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. There were no γ-rays observed during the ~1-month long quenched state, when the radio flux is weakest. These 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.
[en] High-resolution optical spectra of the ultra-luminous X-ray source (ULX) NGC 5408 X-1 show a broad component with a width of ∼750 km s-1 in the He II and Hβ lines in addition to the narrow component observed in these lines and [O III]. Reanalysis of moderate-resolution spectra shows a similar broad component in the He II line. The broad component likely originates in the ULX system itself, probably in the accretion disk. The central wavelength of the broad He II line is shifted by 252 ± 47 km s-1 between the two observations. If this shift represents motion of the compact object, then its mass is less than ∼1800 Msun.
[en] In this paper, we report on Fermi/Large Area Telescope observations of the accreting black hole low-mass X-ray binary V404 Cygni during its outburst in 2015 June–July. Detailed analyses reveal a possible excess of γ-ray emission on 2015 26 June, with a very soft spectrum above 100 MeV, at a position consistent with the direction of V404 Cyg (within the 95 per cent confidence region and a chance probability of 4 × 10-4). This emission cannot be associated with any previously known Fermi source. Its temporal coincidence with the brightest radio and hard X-ray flare in the light curve of V404 Cyg, at the end of the main active phase of its outburst, strengthens the association with V404 Cyg. If the γ-ray emission is associated with V404 Cyg, the simultaneous detection of 511 keV annihilation emission by INTEGRAL reqires that the high-energy γ-rays originate away from the corona, possibly in a Blandford–Znajek jet. Finally, the data give support to models involving a magnetically arrested disc where a bright γ-ray jet can re-form after the occurrence of a major transient ejection seen in the radio.
[en] We obtained three epochs of simultaneous Hubble Space Telescope (HST)/Wide Field Camera 3 and Chandra observations of the ultraluminous X-ray source (ULX) NGC 5408 X-1. The counterpart of the X-ray source is seen in all HST filters, from the UV through the near-IR (NIR), and for the first time, we resolve the optical nebula around the ULX. We identified a small OB association near the ULX that may be the birthplace of the system. The stellar association is young, ∼5 Myr, contains massive stars up to 40 M☉, and is thus similar to associations seen near other ULXs, albeit younger. The UV/optical/NIR spectral energy distribution (SED) of the ULX counterpart is consistent with that of a B0I supergiant star. We are also able to fit the whole SED from the X-rays to the NIR with an irradiated disk model. The three epochs of data show only marginal variability and thus, we cannot firmly conclude on the nature of the optical emission.
[en] We present an analysis of high energy (HE; 0.1-300 GeV) γ-ray observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope, follow-up radio observations with the Australia Telescope Compact Array, Giant Metrewave Radio Telescope and Parkes radio telescopes of the same field and follow-up optical observations with the ESO VLT. We also examine archival XMM-Newton and INTEGRAL X-ray observations of the region around this source. The γ-ray spectrum of 1FGL J1227.9-4852 is best fitted with an exponentially cut-off power law, reminiscent of the population of pulsars observed by Fermi. A previously unknown, compact radio source within the 99.7 per cent error circle of 1FGL J1227.9-4852 is discovered and has a morphology consistent either with an AGN core/jet structure or with two roughly symmetric lobes of a distant radio galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary, also lies within the 1FGL J1227.9-4852 error circle and we report the first detection of radio emission from this source. The potential association of 1FGL J1227.9-4852 with each of these counterparts is discussed. Based upon the available data we find the association of the γ-ray source to the compact double radio source unlikely and suggest that XSS J12270-4859 is a more likely counterpart to the new HE source. We propose that XSS J12270-4859 may be a millisecond binary pulsar and draw comparisons with PSR J1023+0038. (authors)