Publication archive

Publication archive

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a truly international enterprise. While ESA is responsible for the overall mission, the satellite's development and the flight operations, the launcher is provided by the Russian Space Agency and the second ground station is provided by NASA. The scientific instruments and the Science Data Centre are provided by the mission's Principal Investigators, with funding from national organisations.
Published: 02 July 2002
GRS 1747-312 is a bright transient X-ray source in the globular cluster Terzan 6 with quasi-periodic outbursts approximately every 4.5 months. We carried out 260 keV target-of-opportunity observations during eight outbursts with the Proportional Counter Array on the RXTE satellite, for a total exposure time of 301 ks, and detect the first unambiguous thermonuclear X-ray bursts from this source.
Published: 02 July 2003
Measurements of the Lyman alpha column brightness by the Geocoronal Imager (GEO), part of the FUV imaging system on board the IMAGE satellite, have been used to derive an empirical model of the neutral hydrogen density distribution at high altitudes (>3.5 RE geocentric distance) on the night-side of the Earth. The model presented is an effort to provide the density profiles needed to analyze the energetic neutral atom imaging data at ring current altitudes and above. The variable solar Lyman alpha flux is obtained from the UARS/SOLSTICE measurements and the scattered solar Lyman alpha emissions from interplanetary hydrogen are obtained from a model. Assuming that the exosphere at high altitudes (>3.5 RE geocentric distance) can be considered as an optical thin medium and that the hydrogen density profile can be expressed as a double exponential we show that the Lyman alpha column brightness can be converted to hydrogen density profiles. The hydrogen density above 5 RE is found to be slightly higher for large solar zenith angles than for 90° solar zenith angle. The hydrogen density shows temporal variations which are not controlled by any solar quantity or geomagnetic parameter alone. Our Lyman alpha profiles and derived hydrogen density profiles are close to what was observed by Dynamics Explorer 1 [Rairden et al., 1986]. Above 8 RE we find higher densities than they did for all solar zenith angles >90°. We do not find any evidence of depletion due to charge exchange with solar wind protons outside the magnetopause. Our results are only valid above 3.5 RE
Published: 24 July 2003
We present results from two Chandra/ACIS-I observations and one XMM-Newton observation of X-ray emission from the interstellar medium (ISM) and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a beta-model profile with index beta = 0.40 ± 0.04 and a temperature of kBTISM ~ 0.29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray-emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than (kBTSH ~ 2.9 keV) and greatly overpressurized relative to the ambient ISM, indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5, or 2400 km s-1. We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be reenergized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the northeast lobe, implying that there are differences in the dynamics and evolution of the kiloparsec-scale radio components.
Published: 21 July 2003
We present a comprehensive lensing analysis of the rich cluster Cl0024+1654 (z=0.395) based on panoramic sparse-sampled imaging conducted with the WFPC2 and STIS cameras on board the Hubble Space Telescope. By comparing higher fidelity signals in the limited STIS data with the wider field data available from WFPC2, we demonstrate an ability to detect reliably weak lensing signals to a cluster radius of ~5 (h65)-1 Mpc where the mean shear is around 1%.
Published: 10 November 2003
We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. We analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator. The characteristic wave vector directions in this region are nearly parallel to the field lines and the multipoint measurement demonstrates the dynamic character of the chorus source region, changing the Poynting flux direction at time scales shorter than a few seconds. The electric field waveforms of the chorus wave packets (forming separate chorus elements on power spectrograms) show a fine structure consisting of subpackets with a maximum amplitude above 30 mV/m. To study this fine structure we have used a sine-wave parametric model with a variable amplitude.
Published: 10 July 2003
Coordinated data analyses from the initial in-ecliptic phase of the Ulysses mission are presented with special attention given to measurements of particles and fields in interplanetary space. The collection of papers presents the results of observations of large solar flares and effects related to solar wind, and some results are synopsized. The charged-particle instrumentation on the spacecraft is shown to have good dynamic range and energy coverage as demonstrated by a sample proton-energy spectrum.
Published: 20 June 1992
The Ulysses spacecraft encountered Jupiter in February 1992, passing within 6.31 radii of the planet. For approximately 8 days it was inside the Jovian magnetosphere, and for several days before and after that, Ulysses was in the interaction regions formed by the solar wind (the magnetosheath and boundary layer).
Published: 01 December 1993
Proceedings of the 28th ESLAB Symposium, held in Friedrichshafen, Germany, April 19-21, 1994. Ed. Marsden, R.G.
Published: 01 January 1995
Article that appeared in the popular astronomy magazine Sky & Telescope. Unfortunately no preview of the publication exists online. The link from this page, however, will take you to the Sky Publishing website where you purchase a copy of the whole magazine.
Published: 01 March 1996
For much of the past four decades, the scientific probes sent into space stayed relatively close to the equatorial plane of the Sun, which contains the orbits of Earth and other planets. But a few years ago a single craft, Ulysses, ventured out of that thin zone and into the 'polar regions' of interplanetary space.
Published: 01 January 1998
Proceedings of the 34th ESLAB Symposium held 3-6 October 2000 at ESTEC, Noordwijk, The Netherlands. Ed. Marsden, R.G.
Published: 01 March 2001
The Ulysses mission has explored and charted the heliosphere around the minimum in the 11-year cycle of solar activity from a high-latitude perspective. Here, for the first time, is a comprehensive review of the results of that mission. The book furthers our knowledge of the heliosphere near solar minimum and provides the basis for understanding the more complex state of the heliosphere around solar maximum. Amongst other topics, the book covers: the solar wind, the large- and small-scale structure of the heliosphere in 3 dimensions, cosmic rays and energetic particles, interstellar aspects, including cosmic dust. In "The Heliosphere Near Solar Minimum: The Ulysses Perspective", Eds. Balogh, A., Marsden, R.G. & Smith, E.J., Springer-Praxis, Chichester (2001) ISBN 1-85233-204-2, XXV + 411 pp.
Published: 02 May 2001
Vilnius, Lithuania, 2-6 July 2001
Editors: Vladas Vansevicius, Arunas Kucinskas, Jokubas Sudzius
The proceedings are published in Astrophysics and Space Science Vol. 280, Issue 1-2, 2002 (see contents list online - restricted access) and are available online
Published: 01 January 2002
This document summarises the status of the Gaia project at the end of 2002, describing the progress achieved in 2002, and summarising the major ongoing and planned activities in both the scientific and technical areas. It gives references to technical notes prepared by the Gaia scientific community during the year.
Published: 27 January 2003
Proceedings of the conference GAIA SPECTROSCOPY: SCIENCE AND TECHNOLOGY
9-12 September 2002
La Residenza del Sole
Congress Center
Gressoney St. Jean
Aosta
Italy
Published: 02 July 2003
Les Houches Summer School, 14-18 May 2001
Editors: Olivier Bienaymé and Catherine Turon
The proceedings are published in the EAS Publications Series, Volume 2 (2002) and are available online.
Published: 01 January 2002
The scientific case and technical design description on which the mission was accepted within ESA's scientific programme. Note that the design details have been superseded, although the essential instrument principles and design objectives remain unaffected.
Published: 02 March 2001
We present results of an analysis of all 480 ks of Rossi X-ray Timing Explorer Proportional Counter Array data obtained from 17 May 1998 to 11 October 1998 on the luminous low mass X-ray binary GX 13+1. We analysed the spectral properties in colour-colour diagrams (CDs) and hardness-intensity diagrams (HIDs) and fitted the power spectra with a multi-Lorentzian model. GX 13+1 traces out a curved track in the CDs on a time scale of hours, which is very reminiscent of a standard atoll track containing an island, and lower and upper banana branch. However, both count rate and power spectral properties vary along this track in a very unusual way, not seen in any other atoll or Z source. The count rate, which varied by a factor of ~1.6, along a given track first decreases and then increases, causing the motion through the HIDs to be in the opposite sense to that in the CD, contrary to all other Z and atoll sources. Along a CD track, the very low frequency noise uniquely decreases in amplitude from ~5 to ~2% (rms). The high frequency noise amplitude decreases from ~4% to less than 1% and its characteristic frequency decreases from ~10 to ~5 Hz. The 5769 Hz quasi-periodic oscillation (QPO) found earlier is also detected, and no kHz QPOs are found. In addition the entire track shows secular motion on a time scale of about a week. The average count rate as well as the amplitude of the very low frequency noise correlate with this secular motion. We discuss a possible explanation for the peculiar properties of GX 13+1 in terms of an unusual orientation or strength of a relativistic jet.
Published: 02 July 2003
We present an overview of BeppoSAX Wide Field Cameras observations of the nine most frequent type I X-ray bursters in the Galactic center region. Six years of observations (from 1996 to 2002) have amounted to 7 Ms of Galactic center observations and the detection of 1823 bursts. The 3 most frequent bursters are GX354-0 (423 bursts), KS 1731-260 (339) and GS 1826-24 (260). These numbers reflect an unique dataset. We show that all sources have the same global burst behavior as a function of luminosity. At the lowest luminosities (LX < 2 < 1037 erg s1) bursts occur quasi-periodically and the burst rate increases linearly with accretion rate (clear in e.g. GS 1826-24 and KS 1731-260). At Lpers = 2 < 1037 erg s1 the burst rate drops by a factor of five. This corresponds to the transition from, on average, a hydrogen-rich to a pure helium environment in which the flashes originate that are responsible for the bursts. At higher luminosities the bursts recur irregularly; no bursts are observed at the highest luminosities. Our central finding is that most of the trends in bursting behavior are driven by the onset of stable hydrogen burning in the neutron star atmosphere. Furthermore, we notice three new observational fact which are difficult to explain with current burst theory: the presence of short pure-helium bursts at the lowest accretion regimes, the bimodal distribution of peak burst rates, and an accretion rate that is ten times higher than predicted at which the onset of stable hydrogen burning occurs. Finally, we note that our investigation is the first to signal quasi-periodic burst recurrence in KS 1731-260, and a clear proportionality between the frequency of the quasi-periodicity and the persistent flux in GS 1826-24 and KS 1731-260.
Published: 02 June 2003
28-Sep-2020 18:37 UT

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