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eROSITA aboard the Spectrum-Roentgen-Gamma satellite, successfully launched in July 2019, is the first X-ray astronomical telescope operational at the Sun-Earth Lagrange point L2. A prime scientific goal of eROSITA is the detection of 100000 clusters of galaxies, which at the fainter luminosity end appears as weak and slightly extended objects. For a reliable detection and characterization of the sources also a detailed knowledge of the instrumental background is required. In the light of the upcoming ESA Athena mission and other future X-ray missions, eROSITA can play a role as pathfinder in terms of space environment and non-X-ray background at L2.. Initial results related to the eROSITA in-flight background have been obtained during Commissioning and subsequent Calibration and Performance Verification phases. The eROSITA background is composed of various components, such as from the electronics, from particle induced radiation inside the camera, external particles registered (and rejected) onboard, stray-light from celestial sources, and general X-ray background. By means of dedicated variations of the set-up (e.g., filter wheel, on-board processing) and viewing direction we started to disentangle the components and origins. Particle background variations appear to be low, which may be expected due to the low solar activity at the moment. The general background level appears to exceed pre-launch expectation. This is currently under investigation.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the main instrument onboard the Russian/German "Spectrum-Roentgen-Gamma" (SRG) mission which will be operated in an L2 orbit. It will perform the first imaging all-sky survey in the medium energy band. The main scientific goals are a) to detect the hot intergalactic medium of ~100 thousand galaxy clusters and groups and hot gas in filaments between clusters to map out the large scale structure in the Universe for the study of cosmic structure evolution, b) to detect systematically all obscured accreting Black Holes in nearby galaxies and many (up to 3 Million) new, distant active galactic nuclei, and c) to study in detail the physics of galactic X-ray source populations, like pre-main sequence stars, supernova remnants and X-ray binaries. The eROSITA flight model was assembled in 2016 and has successfully passed all acceptance tests on instrument level in the facilities of MPE and IABG in Germany. eROSITA was shipped to NPOL (SRG prime contractor) in January 2017. Currently (May 2018) eROSITA has been integrated on the SRG spacecraft and has successfully passed all functional tests. eROSITA is now awaiting its launch from the Baikonur cosmodrome in spring 2019. The launcher will be a PROTON with an upper stage BLOK-DM.

We present results from the Chandra X-ray Observatory’s characterization of the X-ray emission from Comet 103P/Hartley 2, in support of NASA’s Deep Impact Extended close flyby of the comet on 04 November 2010. The comet was observed 4 times for a total on target time of ∼60 ks between the 17th of October and 16th of November 2010, with two of the visits occurring during the EPOXI close approach on 04 November and 05 November 2010. X-ray emission from 103P was qualitatively similar to that observed for collisionally thin Comets 2P/Encke (Lisse, C.M. et al. [2005]. Astrophys. J. 635, 1329–1347) and 9P/Tempel 1 (Lisse, C.M. et al. [2007]. Icarus 190, 391–405). Emission morphology offset sunward but asymmetrical from the nucleus and emission lines produced by charge exchange between highly stripped C, N, and O solar wind minor ions and coma neutral gas species were found. The comet was very under-luminous in the X-ray at all times, representing the 3rd faintest comet ever detected (LX = 1.1 ± 0.3 × 1014 erg s−1). The coma was collisionally thin to the solar wind at all times, allowing solar wind ions to flow into the inner coma and interact with the densest neutral coma gas. Localization of the X-ray emission in the regions of the major rotating gas jets was observed, consistent with the major source of cometary neutral gas species being icy coma dust particles. Variable spectral features due to changing solar wind flux densities and charge states were also seen. Modeling of the Chandra observations from the first three visits using observed gas production rates and ACE solar wind ion fluxes with a charge exchange mechanism for the emission is consistent with the temporal and spectral behavior expected for a slow, hot wind typical of low latitude emission from the solar corona interacting with the comet’s neutral coma. The X-ray emission during the 4th visit on 16 November 2010 is similar to the unusual behavior seen for Comet 17P/Holmes in 2007 (Christian, D.J. et al. [2010]. Astrophys. J. Suppl. 187, 447–459) as the solar wind became dominated by a less ionized and faster plasma, more typical of outflow from polar coronal hole regions. We postulate that the overall faintness of the comet seen during all visits is due to the unusually well mixed dust and gas content of this hyperactive comet’s coma producing Auger electrons rather than X-rays via charge exchange with the solar wind. An alternative possible explanation for the faintness of the comet’s X-ray emission, and its unusual high CV and unusually low CVI emission, is that the impinging solar wind was drastically slowed in the inner coma, below 150 km s−1, before charge exchanging with cometary neutrals.

Summary of the spectral results obtained with Chandrafor all the comets (denoted by A–H) which were observed from2000 to 2006: a ) the 0.3–1.0 keV pulse height distributions, b )theecliptic latitudes and c ) phases in the solar cycle of the observedcomets,and d )thededuced informationaboutthesolarwindheavyion content. Fig.3a,c,d were adapted from Bodewits et al. (2007). rienced a spectacular outburst, which increased its dust andgasoutflowandopticalbrightnessbyalmostamilliontimeswithin hours,from under17 magto 3 mag, makingit by farthe optically brightest comet observable by Chandra sinceits launch. At the time, comet 17P/Holmes was located at asufficiently high heliographic latitude (19 ◦ ) to be exposedto the polar wind at solar minimum. It was thus expectedthat this comet would exhibit considerably different X-rayproperties, and in fact this was observed: 17P/Holmes be-came the first comet where Chandra did not detect any sig-nificant X-ray emission at all (Christian et al. 2010). Themost likely explanation for this dramatic X-ray faintness isthat the polar wind was so diluted and its ionization so lowthat only very little X-ray flux was generated by charge ex-change at energies above∼300eV. An instrumental effect,i.e., a loss of sensitivity, can definitively be ruled out, be-cause only two months later, another comet, 8P/Tuttle, wasobservedwith Chandra,andthiscomet,at lowlatitude (3

The pn-CCD cameras at the focal plane of the eROSITA space observatory will be the first X-ray (0.2–12 keV) detector to operate in a L-2 orbit. Therefore, no direct information of instrumental non X-ray background (NXB) is available to make predictions for eROSITA. Since, in general, the instrumental NXB experienced in orbit has a major impact on the overall sensitivity of the cameras, we investigated and modeled the L-2 radiation environment and its interaction with the eROSITA mass distribution and cameras, in order to quantify the expected pn-CCD NXB level. We obtain an average value of NXB ∼25% lower than that observed by the pn-CCDs on-board the XMM-Newton satellite, which is placed in a Highly Elliptical Orbit (HEO). We discuss this result in light of the differences between the L-2 and HEO space environments.

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

We report the results of 15 hr of Chandra observations of comet 2P/Encke 2003 on November 24. X-ray emission from comet Encke was resolved on scales of 500-40,000 km, with unusual morphology due to the presence of a low-density, collisionally thin (to charge exchange) coma. A light curve with peak-to-peak amplitude of 20% consistent with a nucleus rotational period of 11.1 hr was found, further evidence for a collisionally thin coma. We confirm emission lines due to oxygen and neon in the 800-1000 eV range but find very unusual oxygen and carbon line ratios in the 200-700 eV range, evidence for low-density, high effective temperature solar wind composition. We compare the X-ray spectral observation results to contemporaneous measurements of the coma and solar wind made by other means and find good evidence for the dominance of a postshock bubble of expanding solar wind plasma, moving at 600 km/s with charge state composition between that of the "fast" and "slow" solar winds.

The volume intensity of the cometary X-ray emission is enhanced behind the bow shock by a factor of up to three. This effect offers the opportunity to identify the bow shock by a tomographic method in X-ray images of comets. By an analysis of the X-ray data obtained by XMM-Newton from Comet C/2000 WM1 (LINEAR) we obtain information on the position, the shape and the structure of the bow shock of this comet. In particular, we get for the first time a global image of the subsolar part of the bow shock, which up to now has not been visited by spacecrafts. The shock is not a sharp discontinuous jump but rather a gradual transition in a region of about 40 000 km width. An asymmetry can well be explained by the inclination of the interplanetary magnetic field. Our results are consistent with theoretical expectations as well as with results from spacecraft observations.

N 51D (= DEM L 192) appears at first glance as a nearly circular, 120 pc diameter bubble of ionized gas around the LMC OB association LH 54. A deeper look reveals a complex web of filaments and deviations from radial expansion. Using a deep XMM-Newton pointing centered on N 51D we find that diffuse soft X-ray emitting gas fills the whole superbubble as delineated by the Hα filaments. Contrary to recent findings for galactic winds, the correlation between Hα and X-ray surface brightness is not good. The X-ray spectrum of this diffuse gas cannot be fitted with the LMC abundance pattern, but implies an overabundance of at least oxygen and neon, consistent with recent enrichment from supernovae Type II. Some indications for enhanced mixing at the brightest region of the Hα shell and for a beginning outflow of the hot gas were also detected.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is now officially scheduled for launch on March 26, 2016. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z < 1 in order to study the large scale structure in the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGN, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars and diffuse emission within the Galaxy. eROSITA is currently (June 2014) in its flight model and calibration phase. All seven flight mirror modules (+ 1 spare) have been delivered and measured in X-rays. The first camera including the complete electronics has been extensively tested (vacuum + X-rays). A pre-test of the final end-toend test has been performed already. So far, all subsystems and components are well within their expected performances.

In an effort to understand the newly discovered phenomenon of cometary X-ray emission, we have obtained observations of the short period (3.3 years), well-studied comet 2P/Encke (Encke) during its July 1997 close approach to Earth. Extended, variable emission on the sunward side of the nucleus was found in the Rontgen X-ray satellite High Resolution Imager (HRI) at 0.090–0.75 keV and in the Extreme Ultraviolet Explorer (EUVE) scanner telescopes' Lexan B 0.090- to 0.28-keV and Al/Ti/C 0.050- to 0.16-keV bandpasses; useful upper limits were found in the Ti/Sb/Al 0.020- to 0.040-eV bandpass. Similar to our results for C/Hyakutake, the emission morphology was roughly symmetric with respect to a vector from the comet's nucleus toward the Sun, with a light curve consisting of a slowly varying baseline emission and a large impulsive event on 7 July 1997 with a time scale of ∼3 h and an amplitude of ∼3 times the baseline. A count rate of ∼0.17 counts s−1 in the HRI was measured for the slowly varying emission, corresponding to a total luminosity Lx of 4×1014 erg s−1. Unlike Hyakutake, however, the bulk of the emission clearly originates outside the comet's bowshock, arguing against the magnetic reconnection and plasma dust emission models. The comet's lightcurve does not correlate with the solar X-ray lightcurve, ruling out scattering of solar X-rays as the emission mechanism. The multiwavelength HRI/EUVE photometry is inconsistent with the Haberli et al. (1997, Science 276, 939–942) charge transfer, plasma dust, and attogram dust models of cometary X-ray emission and is consistent with the Wegmann et al. (1988, Planet. Space Sci. 46, 603–612) charge exchange, 0.15- to 0.45-keV thermal bremsstrahlung, and photon index 1.6–2.0 power law models. While the impulsive event correlates very well with the passage of a solar magnetic field boundary at the Earth and an increase in the solar wind particle flux, it is not coincident, according to current models of the solar wind magnetic current sheet, with the passage of the sector boundary by the comet, suggesting that new models of the current sheet are necessary.

Results are presented from the first five years of the high precision RV survey carried out with the 1.4m CAT+CES spectrograph at ESO La Silla. This RV survey of 37 solar-type stars was begun in Nov. 1992. Using an iodine gas absorption cell for self-calibration we currently achieve a long-term precision of 20 m/s in a 30-min exposure of a 5.5 mag star. This value is the typical ‘working’ precision in survey work, i.e. an average over all observing conditions.We present the RV data for our most variable star, ι Hor (G0V), with a possible periodicity of 600 d that could imply a companion of minimum mass m sin i = 2.0 MJup. However, these data are severely complicated by stellar activity to which a large part of the variability must be attributed. Our RV data for ϕ2 Pav (F8V) contain a possible period of 43 d which would imply a planet with m sin i = 0.69 MJup. It must be stressed that for both stars the significance of the periods is still insufficient to conclude that planets are indeed orbiting them. We also show our data for a Hipparcos astrometric brown dwarf candidate, GJ 570A, that do not confirm expectations for a correspondingly high RV signal. Longer monitoring of the star is required in order to confirm a possible low amplitude variation.

The discovery of X-ray emission from comets has created a number of questions about the physical mechanism producing the radiation. There are now a variety of explanations for the emission, from thermal bremsstrahlung of electrons off neutrals or dust, to charge exchange induced emission from solar wind ions, to scattering of solar X-rays from attogram dust, to reconnection of solar magnetic field lines. In an effort to understand this new phenomenon, we observed but failed to detect in the X-ray the very dusty and active comet C/Hale-Bopp 1995 O1 over a two year period, September 1996 to December 1997, using the ROSAT HRI imaging photometer at 0.1–2.0 keV and the ASCA SIS imaging spectrometer at 0.5–10.0 keV. The results of our Hale-Bopp non-detections, when combined with spectroscopic imaging 0.08–1.0 keV observations of the comet by EUVE and BeppoSAX, show that the emission has the same spectral shape and strong variability seen in other comets. Comparison of the ROSAT photometry of the comet to our ROSAT database of 8 comets strongly suggests that the overall X-ray faintness of the comet was due to an emission mechanism coupled to gas, and not dust, in the comet’s coma.

During its close approach to Earth, comet C/Hyakutake 1996 B2 was observed at extreme ultraviolet and x-ray wavelengths with the Rœntgen X-ray Satellite and Rossi X-ray Timing Explorer. The emission morphology was symmetric with respect to a vector from the comet's nucleus toward the sun, but not symmetric around the direction of motion of the comet with respect to interplanetary dust. A slowly varying emission and a large impulsive event that varied on time scales of 1 to 2 hours were observed. An interaction between the comet and the solar wind/solar magnetic field seems to be the most likely mechanism for the observed emission.

We report on the progress of a program to search for extra-solar planets using high precision radial velocity (RV) measurements taken at the European Southern Observatory. Instrumental errors in the radial velocity measure are minimized by placing a temperature stabilized molecular iodine absorption cell in front of the entrance slit to the spectrograph. This imposes an iodine absorption spectrum on top of the stellar spectrum. All stellar radial velocity shifts are measured with respect to the iodine absorption spectrum. The current program consists of a sample of 26 F, G, and K dwarfs and 1 dMe star. Radial velocity measurements taken since November 1992 indicate that a typical long-term radial velocity precision for this program is about 18 m s−1. One of our program stars, τ Cet, shows constant radial velocity variability with a scatter of 6 m s−1. Representative radial velocity measurements are given for three stars showing no significant radial velocity variations, three stars showing variations indicative of low mass companions, and for the triple system α Cen. The radial velocity measurements of α Cen A and B are consistent with the astrometric orbital solution, although the data points have a slightly steeper slope than the calculated orbit. Continued radial velocity monitoring of this star should eventually result in a better orbital solution.

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ∼16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. Fil: Meech, K. J.. Institute for Astronomy; Estados Unidos Fil: A’Hearn, M. F.. University of Maryland; Estados Unidos Fil: Adams, J. A.. Cornell University; Estados Unidos Fil: Bacci, P.. Centro Astronomico di Libbiano; Italia Fil: Bai, J.. Chinese Academy of Sciences; China Fil: Barrera, L.. Universidad Metropolitana de Ciencias de la Educacion; Chile Fil: Battelino, M.. Swedish Space Corporation; Suecia Fil: Bauer, J. M.. Jet Propulsion Laboratory; Estados Unidos Fil: Becklin, E.. Stratospheric Observatory for Infrared Astronomy; Estados Unidos Fil: Bhatt, B.. Indian Institute of Astrophysics; India Fil: Biver, N.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bockelee Morvan, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bodewits, D.. University of Maryland; Estados Unidos Fil: Bohnhardt, H.. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; Alemania Fil: Boissier, J.. Inst. di Radioastronomia; Italia Fil: Bonev, B. P.. Catholic University of America; Estados Unidos Fil: Borghini, W.. Osservatorio Astronomico Naturalistico di Casasco; Italia Fil: Brucato, J. R.. Osservatorio Astrofisico di Arcetri; Italia Fil: Bryssinck, E.. Brixiis Observatory; Bélgica Fil: Buie. M. W.. Southwest Research Institute; Estados Unidos Fil: Canovas, H.. Utrecht University; Países Bajos Fil: Castellano, D.. Unione Astrofili Italiani; Italia Fil: Charnley, S. B.. National Aeronautics And Space Administration; Estados Unidos Fil: Chen, W. P.. National Taiwan Normal University; Corea del Sur Fil: Chiang, P.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Choi, Y. J.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Christian, D. J.. California State University; Estados Unidos Fil: Chuang, Y. L.. National Taiwan Normal University; Corea del Sur Fil: Cochran, A. L.. University of Texas; Estados Unidos Fil: Melita, Mario Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies. At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1–2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles. This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun. Processes of production of solar system X-rays are discussed and an overview is provided of the main source mechanisms of X-ray production at each object. A brief account on recent development in the area of laboratory studies of X-ray production is also provided.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum‐Roentgen‐Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max‐Planck‐Society.The design driving science is the detection of 50–100 thousands Clusters of Galaxies up to redshift z∼1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all‐sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter‐I telescope modules, each equipped with 54 Wolter‐I shells having an outer diameter of 360 mm. This would provide and effective area at 1.5 keV of ∼1500 cm2 and an on axis PSF HEW of 15″ which would provide an effective angular resolution of 25″–30″. In the focus of each mirror module, a fast frame‐store pn‐CCD will provide a field of view of 1° in diameter for an active FOV...

Scattering of solar X-ray radiation mainly produces the non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn. Recently X-ray flares are observed from the low-latitude disk of giant planets Jupiter and Saturn in the energy range of 0.2-2 keV. These flares are found to occur in tandem with the occurrence of solar X-ray flare, when light travel time delay is accounted, suggesting that X-rays from these planets can be used to study flaring on the hemisphere of the Sun invisible to near-Earth space weather satellites. Also by proper modeling of the observed planetary X-rays the solar soft X-ray flux can be derived. X-ray flares are also observed recently from Mars in direct response to solar flares. The X-ray emission from comets, the heliosphere, the geocorona, and the Martian and Venusian halo are all largely driven by charge exchange collision between highly ionized minor heavy ions in the solar wind and gaseous neutral species in the bodies' atmosphere or exosphere - a process known as solar wind charge exchange (SWCX). In particular, the cometary X-ray spectrum can be used to derive abundances of high-charge state ions of O, C, Ne as well as the speed of the solar wind. Thus cometary X-rays can provide a diagnostic of the solar wind properties even at far off distances from the Earth. This paper provides a brief overview of X-rays from some of the solar system bodies and their connection with solar X-rays and solar wind, and how planetary and cometary X-rays can be used to study the solar X-ray radiation and solar wind properties.

From 29 October to 3 November 1991 we performed a 46 000 sec ROSAT PSPC observation of the northern part of the Large Magellanic Cloud containing the X-ray binary LMC X-4. Here we present first results of this pointed observation on LMC X-4. We also show the light curve of LMC X-4 obtained during the ROSAT all-sky survey which allowed its 30-day modulation to be followed for more than 50 days. In particular, these observations indicate that the length of the 30-day cycle of LMC X-4 is decreasing with time.

The X-ray Observatory XMM-Newton is in orbit since December 1999. We will report on the current status of the in-flight spectral calibration of the EPIC-pn camera. Using the internal calibration source and line spectra of supernova remnants the calibration of the energy scale has been monitored over the first years of operations. Continuum spectra of celestial objects like Active Galactic Nuclei or isolated neutron stars were used for cross-calibrating the instruments. We report on recent improvements in the spectral calibration as well as still existing problems.

We report on the current status of the background calibration of the EPIC pn-CCD camera on board XMM-Newton. The intrinsic background is comprised of internal electronic noise, and continuous and fluorescent X-ray emission induced by high-energy particles. Soft protons passing through the X-ray telescope (and finally also true cosmic X-rays) contribute to the registered events. The camera background has been monitored by using data in closed filter positions for three years; we review the spectral, spatial, and temporal distribution, for all commissioned instrument modes. This paper also discusses briefly the effects on scientific data analysis and conclusions for further observations and detectors.

The observation of comet C/2000 WM1 (LINEAR) with XMM-Newton is a highlight in the field of cometary research. During 17 hours of almost uninterrupted observations, more than one million photons were recorded with unprecedented spectral resolution. The results obtained so far clearly demonstrate that the X-ray emission is caused by charge exchange reactions between highly charged heavy ions in the solar wind - mainly oxygen and carbon - and cometary gas. Due to the high number of detected photons, an investigation of the X-ray morphology is also possible in considerable detail. The observation was also a highlight from the technological point of view, demonstrating that XMM-Newton has more capabilities than are currently utilized. In order to follow the comet, the orientation of the satellite had to be adjusted several times. This was done by just changing the guide star offsets, leaving the X-ray instruments switched on. Compared to the usual procedure with regular slews, where the X-ray instruments are reinitialized afterwards, this new technique increased the time available for scientific observations by 34% for MOS and by 83% for PN. The capability of performing quick attitude adjustments during an observation may be of interest also for other astrophysical applications.

XMM-Newton, the most powerful X-ray telescope ever built was launched from the european space port Kourou on december 10 last year. Three large X-ray Wolter type mirror systems are focusing the incoming X-rays from 100 eV up to 15,000 eV onto the focal instruments: fully depleted backside illuminated pn-CCDs and frontside illuminated MOS-CCDs. The concept of the pn-CCD camera will be briefly described and its performance on ground and in orbit will be shown. Special emphasis will be given to the radiation hardening of the devices, to the instrument background and to the experience of charged particle background in space. A comparison of the performance on ground and after 5 months in space will be shown.

On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we started the Calibration and Performance Verification Phase, which will last until the end of May 2000. In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit performance of the camera. We also show some of the early results with the pn-camera, the first light image of a region in the Large Magellanic Cloud, and an observation of the Crab Nebular.

When comet Hyakutake (C/1996 B2) encountered Earth in March 1996 at a minimum distance of only 15 million kilometers (40 times the distance of the moon), x-ray and extreme ultraviolet emission was discovered for the first time from a comet. The observations were performed with the astronomy satellites ROSAT and EUVE. A systematic search for x-rays from comets in archival data, obtained during the ROSAT all-sky survey in 1990/91, resulted in the discovery of x-ray emission from four additional comets. They were detected at seven occasions in total, when they were optically 300 to 30 000 times fainter than Hyakutake. These findings indicated that comets represent a new class of celestial x-ray sources. Subsequent detections of x-ray emission from additional comets with the satellites ROSAT, EUVE, and BeppoSAX confirmed this conclusion. The x-ray observations have obviously revealed the presence of a process in comets which had escaped attention until recently. This process is most likely charge exchange bet...

The main strengths of ROSAT [1] are its high quality imaging of extended sources and its large sensitivity for the detection of point sources. In the all-sky survey the diffuse X-ray emission was mapped with a resolution of 12 arcmin [2]. The number of point sources detected in the survey is ≈ 80000 [3]. In addition more than 80000 sources have been found in the ≈ 6 500 fields observed with the PSPC and HRI until now in the course of the pointed programme. A wealth of information about source variabilities has been extracted both from the all-sky survey and from the pointed observations, as well as from a combination of both. The outcome of correlation studies on source variabilities has been given by Voges and Boiler 1997, cf. Fig. 1 [4].

We report on the timing analysis of the high-mass X-ray binary (HMXRB) LMC X-4 with the ROSAT satellite. The observation covers about three binary orbits in the high-intensity state of the 30 day cycle of LMC X-4, thus allowing an accurate determination of the pulse period and the orbital parameters of the 13.5 s X-ray pulsar. The new mid-eclipse epoch, combined with the previous epochs, suggests orbital decay in LMC X-4 at a rate of orb/Porb ~ -5 × 10-7 yr-1. An interpretation of our results is discussed in the context of conservative mass loss and tidal evolution and in comparison with the other HMXRB Cen X-3.