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تسجيل مستخدم جديدHighlights from XMM-Newton
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The launch of the Chandra (NASA) and XMM-Newton (ESA) X-ray observatories in 1999 has revolutionized our view of the Universe, by providing astrophysical information about many classes of sources with unprecedent detail. The high throughput of XMM-Newton makes it the ideal instrument to provide low to moderate resolution spectroscopy of faint and extended sources. After 3 years of operations, XMM-Newton has observed many types of astronomical sources and delivered very interesting results in many areas. In this review, we highlight a few points where the contribution of XMM-Newton has significantly furthered our knowledge of the energetic Universe.
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XMM-Newton has observed the X-ray sky since early 2000. The XMM-Newton Survey Science Centre Consortium has published catalogues of X-ray and ultraviolet sources found serendipitously in the individual observations. This series is now augmented by a
catalogue dedicated to X-ray sources detected in spatially overlapping XMM-Newton observations. The aim of this catalogue is to explore repeatedly observed sky regions. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate long-term flux variability directly through the source detection process. A new standardised strategy for simultaneous source detection on multiple observations is introduced. It is coded as a new task within the XMM-Newton Science Analysis System and used to compile a catalogue of sources from 434 stacks comprising 1,789 overlapping XMM-Newton observations that entered the 3XMM-DR7 catalogue, have a low background and full-frame readout of all EPIC cameras. The first stacked catalogue is called 3XMM-DR7s. It contains 71,951 unique sources with positions and parameters such as fluxes, hardness ratios, quality estimates, and information on inter-observation variability. About 15% of the sources are new with respect to 3XMM-DR7. Through stacked source detection, the parameters of repeatedly observed sources can be determined with higher accuracy than in the individual observations. The method is more sensitive to faint sources and tends to produce fewer spurious detections. With this first stacked catalogue we demonstrate the feasibility and benefit of the approach. It supplements the large data base of XMM-Newton detections by additional, in particular faint, sources and adds variability information. In the future, the catalogue will be expanded to larger samples and continued within the series of serendipitous XMM-Newton source catalogues.
We have attempted to analyse all the available data taken by XMM-Newton as it slews between targets. This slew survey, the resultant source catalogue and the analysis procedures used are described in an accompanying paper. In this letter we present t
he initial science results from the survey. To date, detailed source-searching has been performed in three X-ray bands (soft, hard and total) in the EPIC-pn 0.2-12 keV band over ~6300 sq.degrees (~15% of the sky), and of order 4000 X-ray sources have been detected (~55% of which have IDs). A great variety of sources are seen, including AGN, galaxies, clusters and groups, active stars, SNRs, low- and high-mass XRBs and white dwarfs. In particular, as this survey constitutes the deepest ever hard-band 2-12 keV all-sky survey, a large number of hard sources are detected. Furthermore, the great sensitivity and low-background of the EPIC-pn camera are especially suited to emission from extended sources, and interesting spatial structure is observed in many supernova remnants and clusters of galaxies. The instrument is very adept at mapping large areas of the X-ray sky. Also, as the slew survey is well matched to the ROSAT all-sky survey, long-term variability studies are possible, and a number of extremely variable X-ray sources, some possibly due to the tidal disruption of stars by central supermassive black holes, have been discovered.
NA60 measured dimuon production in p-A and In-In collisions at the CERN SPS. This paper presents a high statistics measurement of $phi$ meson production in In-In collisions at 158 AGeV. Both the transverse momentum, rapidity, decay angular distributi
ons and the absolute yield were measured as a function of centrality. The results are compared to previous measurements in order to shed light on the long standing $phi$ puzzle. In addition, highlights on $eta$ meson production and on the dimuon excess below the J/$psi$ mass are presented.
We have analysed four ASCA observations (1994--1995, 1996--1997) and three XMM-Newton observations (2005) of this source, in all of which the source is in high/soft state. We modeled the continuum spectra with relativistic disk model kerrbb, estimate
d the spin of the central black hole, and constrained the spectral hardening factor f_col and the distance. If kerrbb model applies, for normally used value of f_col, the distance cannot be very small, and f_col changes with observations.
We investigate the properties of a variability-selected complete sample of AGN in order to identify the mechanisms which cause large amplitude X-ray variability on time scales of years. A complete sample of 24 sources was constructed, from AGN which
changed their soft X-ray luminosity by more than one order of magnitude over 5--20 years between ROSAT observations and the XMM Slew Survey. Follow-up observations were obtained with the Swift satellite. After removal of two probable spurious sources, we find that the sample has global properties which differ little from a non-varying control sample drawn from the wider XMM-Slew/ROSAT/Veron sample of all secure AGN detections. A wide range of AGN types are represented in the varying sample. The black hole mass distributions for the varying and non-varying sample are not significantly different. This suggests that long timescale variability is not strongly affected by black hole mass. There is marginal evidence that the variable sources have a lower redshift (2$sigma$) and X-ray luminosity (1.7$sigma$). Apart from two radio-loud sources, the sample have normal optical-X-ray ratios ($alpha_{rm OX}$) when at their peak but are X-ray weak during their lowest flux measurements. Drawing on our results and other studies, we are able to identify a variety of variability mechanisms at play: tidal disruption events, jet activity, changes in absorption, thermal emission from the inner accretion disc, and variable accretion disc reflection. Little evidence for strong absorption is seen in the majority of the sample and single-component absorption can be excluded as the mechanism for most sources.
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