Publication archive

Publication archive

We report the results of two XMM-Newton observations of the ultra-compact low-mass X-ray binary 4U 1850-087 located in the galactic globular cluster NGC6712. A broad emission feature at 0.7 keV was detected in an earlier ASCA observation and explained as the result of an unusual Ne/O abundance ratio in the absorbing material local to the source. We find no evidence for this feature and derive Ne/O ratios in the range 0.14-0.21, consistent with that of the interstellar medium. During the second observation, when the source was ~10% more luminous, there is some evidence for a slightly higher Ne/O ratio and additional absorption. Changes in the Ne/O abundance ratio have been detected from another ultra-compact binary, 4U 1543-624. We propose that these changes result from an X-ay induced wind which is evaporated from an O and Ne rich degenerate donor. As the source X-ray intensity increases so does the amount of evaporation and hence the column densities and abundance ratio of Ne and O.
Published: 21 November 2005
We present the results of a long (~93 ks) XMM-Newton observation of the bright BL-Lac object PKS 0548-322 (z= 0.069). Our Reflection Grating Spectrometer (RGS) spectrum shows a single absorption feature at an observed wavelength lambda= 23.33 +/- 0.01 Å, which we interpret as OVI Kalpha absorption at z= 0.058, i.e. ~3000 km s-1 from the background object. The observed equivalent width of the absorption line, ~30 mÅ, coupled with the lack of the corresponding absorption edge in the EPIC pn data, implies a column density of NOVI ~ 2 x 1016 cm-2 and turbulence with a Doppler velocity parameter b > 100 km s-1. Within the limitations of our RGS spectrum, no OVII or OV Kalpha absorption are detected. Under the assumption of ionization equilibrium by both collisions and the extragalactic background, this is only marginally consistent if the gas temperature is ~2.5 x 105 K, with significantly lower or higher values being excluded by our limits on OV or OVII. If confirmed, this would be the first X-ray detection of a large amount of intervening warm absorbing gas through OVI absorption. The existence of such a high column density absorber, much stronger than any previously detected one in OVI, would place stringent constraints on the large-scale distribution of baryonic gas in the Universe.
Published: 16 June 2005
We present lightcurves obtained in X-ray by the XMM-Newton EPIC cameras and simultaneous radio lightcurves obtained with the VLA for five active M-type flare stars. A number of flare events were observed, and by comparing radio with X-ray data, we consider various possible flare mechanisms. In cases where there seems to be a clear correlation between radio and X-ray activity, we use an energy budget argument to show that the heating which leads to the X-ray emission could be due to the same particles emitting in the radio. In cases where there is radio activity without corresponding X-ray activity, we argue that the radio emission is likely to arise from coherent processes involving comparatively few particles. In one case, we are able to show from polarization of the radio emission that this is almost certainly the case. Cases for which X-ray activity is seen without corresponding radio activity are more difficult to explain. We suggest that the heating particles may be accelerated to very high energy, and the resulting synchrotron radio emission may be beamed in directions other than the line of sight.
Published: 16 June 2005
The two Reflection Grating Spectrometers on board ESA's XMM-Newton X-ray satellite are designed to perform high resolution X-ray spectroscopy in the range [0.3-2.1] keV. The most-commonly used operation mode for scientific observations with the RGS is the Spectroscopy Mode. It includes on-board thresholds, hot pixel and column rejection using look-up tables and rejection of cosmic events. In Diagnostic Mode, this on-board data processing is completely by-passed and full images of the CCDs are transferred to ground. These data are then used for dark current, system noise level calibration and hot pixel / column detection. Diagnostic images are also normally obtained during Spectroscopy observations interleaved at a low frequency. We have developed IDL based interactive tools for Diagnostic data analysis, with the main aims of establishing system noise calibration and hot pixel and columns detection, as well as for instrument health monitoring purposes. The RGS Diagnostic Tools can be run individually on single diagnostic images, but are mostly used in batch mode per revolution for populating a database. Interactive analysis and batch tools then interact with the database for parameter extraction and temporal analysis. The Tools produce also several graphical and numerical outputs, which are used on a web-based integrated system for fast diagnostic and trend monitoring. In addition IDL tools are available for the monitoring of the quality of the science data in spectroscopy mode. Data from the onboard calibration source is extracted and used to monitor the gain and contamination of the instrument. These tools build also a database to monitor long term changes in the instrument response.
Published: 02 May 2005
On 10 December 2004, it was five years since ESA's XMM-Newton observatory was successfully put into orbit. It is therefore time to stand back and ask where we stand with the scientific results and what new perspectives the mission has brought us. The answers are to be found in more than 700 publications in the refereed literature and the manifold oversubscription for every observing Announcement of Opportunity for the mission.
Published: 16 May 2005
We report on XMM-Newton observations of two X-ray transient millisecond pulsars (XRTMSPs). We detected XTE J0929-314 with an unabsorbed luminosity of ~ 7x 1031 erg s-1 (0.5-10 keV) at a fiducial distance of 10 kpc. The quiescent spectrum is consistent with a simple power law spectrum. The upper limit on the flux from a cooling neutron star atmosphere is about 20% of the total flux. XTE J1807-294 instead was not detected. We can put an upper limit on the source quiescent 0.5-10 keV unabsorbed luminosity ~< 4x1031 erg s-1 at 8 kpc. These observations strenghten the idea that XRTMSPs have quiescent luminosities significantly lower than classical neutron star transients.
Published: 16 May 2005
In an analysis of XMM-Newton archival observations of the bright Local Group spiral galaxy M 31 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2-4.5 keV luminosity of 4.4 x 1034 . EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 856 sources in an area of 1.24 square degrees. We correlate our sources with earlier M 31 X-ray catalogues and use information from optical, infra-red and radio wavelengths. As sources within M 31 we detect 21 supernova remnants (SNR) and 23 SNR candidates, 18 supersoft source (SSS) candidates, 7 X-ray binaries (XRBs) and 9 XRB candidates, as well as 27 globular cluster sources (GlC) and 10 GlC candidates, which most likely are low mass XRBs within the GlC. Comparison to earlier X-ray surveys reveal transients not detected with XMM-Newton, which add to the number of M 31 XRBs. There are 567 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 31 or background AGN. The number of 44 SNRs and candidates more than doubles the X-ray-detected SNRs. 22 sources are new SNR candidates in M 31 based on X-ray selection criteria. Another SNR candidate may be the first plerion detected outside the Galaxy and the Magellanic Clouds. On the other hand, six sources are foreground stars and 90 foreground star candidates, one is a BL Lac-type active galactic nucleus (AGN) and 36 are AGN candidates, one source coincides with the Local Group galaxy M 32, one with a background galaxy cluster (GCl) and another is a GCl candidate, all sources not connected to M 31.
Published: 16 May 2005
XMM-Newton EPIC observations of PSR B0656+14, PSR B1055-52, and Geminga have substantially increased the collection of statistics available for these three isolated neutron stars, so apparently similar to deserve the nickname of the Three Musketeers, given to them by Becker & Trumper. Here we take advantage of the EPIC statistics to perform phase-resolved spectroscopy for all three objects. The phase-averaged spectrum of the Three Musketeers is best described by a three-component model. This includes two blackbody components -a cooler one, possibly originating from the bulk of the star surface, and a hotter one, coming from a smaller portion of the star surface (a "hot spot") -plus a power law. The relative contributions of the three components are seen to vary as a function of phase, as the stars' rotation brings into view different emitting regions. The hot spots, which have very different apparent dimensions (in spite of the similarity of the three neutron stars polar cap radii) are responsible for the bulk of the phase variation. The amplitude of the observed phase modulation is also markedly different for the three sources. Another striking aspect of our phase-resolved phenomenology is the apparent lack of any common phase alignment between the observed modulation patterns for the two blackbody components. They are seen to vary in phase in the case of PSR B1055-52 but in antiphase in the case of PSR B0656+14. These findings do not support standard and simplistic models of neutron star magnetic field configuration and surface temperature distribution.
Published: 21 April 2005
We present the analysis of XMM-Newton observations of three X-ray weak quasars: PG 1001+054, PG1535+547 and PG 2112+059. All objects are absorbed by ionized material showing high column densities, NH = 2.9 x 1022 cm-2 to NH = 1.9 x 1023 cm-2, and ionization parameters, xi = 147 erg cm s-1 to xi = 542 erg cm s-1. The spectra of PG1535+547 requires an additional partial covering by neutral material with a column density of NH approx 9 x 1022 cm-2 at a covering factor of approx 0.96. The spectra of PG1535+547 show systematic residuals in the energy range from sim 4 keV to sim 6 keV, which are inconsistent with Kalpha-fluorescence-emission of neutral or ionized iron under the assumption of a Gaussian line profile. They can be described with a relativistic disk line (Laor) and establish therefore the second X-ray weak quasar with such a spectral characteristic. Our results together with the findings of Brinkmann et al. (2004) and Piconcelli et al. (2004a), indicate that warm absorbers characterized by high column densities and ionization parameters are typical of X-ray weak quasars. The occurrence of a variable relativistic broad Fe Kalpha fluorescence line in two out of the five well studied X-ray weak quasars might indicate a second general characteristic of the entire object class. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.
Published: 07 April 2005
We present a 30 ks XMM-Newton observation of the z = 2.35 Type II radio quiet quasar RXJ1343.4+0001. These data provide the first good quality X--ray spectrum for this object. We measured a continuum slope Gamma = 1.85+/-0.10 with only an upper limit on the column density of the absorbing material of Nh <~ 10e22 cm-2 as well as a Fe K_alpha emission line at the 3sigma confidence level. We do not find therefore a highly absorbed object neither a truly flat spectrum as suggested on the basis of previous less sensitive ROSAT and ASCA measurements.
Published: 20 March 2005
We present results of a systematic analysis of the XMM-Newton spectra of 40 quasars (QSOs) (z<~1.72) from the Palomar-Green (PG) Bright Quasar Survey sample (MB<-23). The sample includes 35 radio-quiet quasars (RQQs) and 5 radio-loud quasars (RLQs). The analysis of the spectra above 2 keV reveals that the hard X-ray continuum emission can be modeled with a power law component with = 1.89+/-0.11 and = 1.63(+0.02,-0.01) for the RQQs and RLQs, respectively. Below 2 keV, a strong, broad excess is present in most QSO spectra. This feature has been fitted with four different models assuming several physical scenarios. All tested models (blackbody, multicolor blackbody, bremsstrahlung and power law) satisfactorily fitted the majority of the spectra. However, none of them is able to provide an adequate parameterization for the soft excess emission in all QSOs, indicating the absence of an universal shape for this spectral feature. An additional cold absorption component was required only in three sources. On the other hand, as recently pointed out by Porquet et al. (2004) for a smaller sample of PG QSOs, warm absorber features are present in ~50% of the QSO spectra in contrast with their rare occurrence (~5-10%) found in previous studies. The XMM-Newton view of optically-selected bright QSOs therefore suggests that there are no significant difference in the X-ray spectral properties once compared with the low-luminosity Seyfert 1 galaxies. Properties of the Fe Kalpha emission lines are presented in a companion paper.
Published: 10 March 2005
During Nov. 26-29, 2003 XMM-Newton observed soft (0.2-2 keV) X-ray emission from Jupiter for 69 hours. The low-latitude X-ray disk emission of Jupiter is observed to be almost uniform in intensity with brightness that is consistent with a solar-photon driven process. The simultaneous light curves of Jovian equatorial X rays and solar X rays (measured by the TIMED/SEE and GOES satellites) show similar day-to-day variability. A large solar X-ray flare occurring on the Jupiter-facing side of the Sun is found to have a corresponding feature in the Jovian X rays. These results support the hypothesis that X-ray emission from Jovian low-latitudes are solar X rays scattered from the planet's upper atmosphere, and suggest that the Sun directly controls the non-auroral X rays from Jupiter's disk. Our study also suggests that Jovian equatorial X rays can be used to monitor the solar X-ray flare activity on the hemisphere of the Sun that is invisible to space weather satellites.
Published: 18 January 2005
We present Chandra and XMM-Newton observations of a small sample (11 objects) of optically-selected Seyfert 2 galaxies, for which ASCA and BeppoSAX had suggested Compton-thick obscuration of the Active Nucleus (AGN). The main goal of this study is to estimate the rate of transitions between "transmission-" and "reprocessing-dominated" states. We discover one new transition in NGC4939, with a possible additional candidate in NGC5643. This indicates a typical occurrence rate of at least 0.02/year. These transitions could be due to large changes of the obscuring gas column density, or to a transient dimming of the AGN activity, the latter scenario being supported by detailed analysis of the best studied events. Independently of the ultimate mechanism, comparison of the observed spectral dynamics with Monte-Carlo simulations demonstrates that the obscuring gas is largely inhomogeneous, with multiple absorbing components possibly spread through the whole range of distances from the nucleus between a fraction of parsecs up to several hundreds parsecs. As a by-product of this study, we report the first measurement ever of the column density covering the AGN in NGC3393, and the discovery of soft X-ray extended emission, apparently aligned along the host galaxy main axis in NGC5005. The latter object hosts most likely an historically misclassified low-luminosity Compton-thin AGN.
Published: 07 January 2005
We report the XMM-Newton discovery of a X-ray bright AGN pair in the interacting galaxy system ESO509-IG066. Both galaxies host an X-ray luminous (LX ~ 1043 erg/s) obscured nucleus with column densities NH ~ 7x1022 and NH ~ 5 x 1021 atoms.cm-2. The optical morphology is only mildly disturbed, suggesting a merging system in the early stage of its evolution. Still, the pair is probably gravitationally bound, and might eventually evolve into a compact, fully gas embedded systems such as NGC6240.
Published: 03 January 2005
We present X-ray spectra of the nucleus of the nearby radio galaxy Centaurus A from observations with the XMM-Newton EPIC CCD cameras (two exposures separated by 12 months) and the Chandra HETGS. For the first time in an FR I type galaxy, we resolve fluorescent K alpha emission from cold, neutral, or near-neutral iron at 6.4 keV, with an rms line width of ~20 eV. The Fe line parameters observed are consistent with fluorescent emission from material at a large distance from the active galactic nucleus, either in the form of an absorber that nearly completely surrounds the central engine or a torus that lies predominantly out of the line of sight. Unresolved emission lines from neutral Si K alpha at 1.74 keV and neutral S K alpha at 2.30 keV are also detected. We find no evidence in the data for a previously reported 6.8 keV broadened Fe line. The continuum spectrum is well fitted with a combination of a heavily absorbed power-law component that we relate, using Bondi theory, to accretion phenomena in the form of a standard, geometrically thin, optically thick disk, and a second, less absorbed, power-law component that we associate with emission from the subparsec VLBI radio jet.
Published: 11 September 2004
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
The XMM (X-ray Multi-Mirror) spacecraft, a space-borne X-ray observatory to be launched by Ariane-5 in 1999, stands 10 m-high and measures over 4 m in diameter in launch configuration, for a launch mass of just under 4 tonnes. Such a tall spacecraft challenges the capabilities of existing European environmental testing facilities. The spacecraft design does allow for a relatively straightforward splitting into modules. The Structural and Thermal Model (STM) of the XMM spacecraft has successfully undergone mechanical environmental testing at the European Space Research & Technology Centre (ESTEC). This article briefly introduces the XMM project, presents an overview of the XMM configuration constraints, explains the spacecraft-level model philosophy and mechanical test flow, and summarises the present status of the tests performed.
Published: 02 April 1998
The XMM satellite will be launched in August 1999 and a simulator has been developed to test and validate the supporting ground segment. Due to the very tight schedule and the high fidelity of the modelling required, this development effort has provided numerous unique challenges. This article details these challenges and the approaches that have been taken in meeting them, as well as the simulator's architecture and current status.
Published: 02 May 1998
Product Assurance has both a preventative and a corrective role in terms of quality control in a spacecraft project. This article summarises how it was approached within the XMM project, what unforeseen problems were encountered, and what lessons can be learned from our experience.
Published: 01 December 1999
The XMM (X-ray Multi-Mirror) spacecraft, a spaceborne X-ray observatory to be launched by Ariane-5, stands 10 m high and measures over 4 m in diameter in launch configuration, for a launch mass of just under four tons. Such a tall spacecraft challenges the capabilities of existing European environmental testing facilities. Provisions were made in the design for a split according to geometry into an Upper Module and a Lower Module for environmental test purposes. Optical testing of the X-ray Mirror Modules - the core technological challenge - required the use of several existing and custom-built test facilities. In the face of strict schedule requirements, spacecraft-level test flows were organised around extensively parallel flows and all tests were scrutinised for their potential for early problem identification. This article briefly introduces the XMM configuration and schedule constraints, explains the spacecraft-level model philosophy, discusses the consequences for each category of test in terms of facility and test specimen configurations, and summarises the spacecraft test flows and the results achieved.
Published: 01 December 1999
8-Dec-2021 05:45 UT

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