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Super Soft X-ray Sources (SSS) are powered by nuclear burning on the surface of an accreting white dwarf, they are seen around 0.1-1 keV (thus in the soft X-ray regime), depending on effective temperature and the amount of intervening interstellar neutral hydrogen N_H. The most realistic model to derive physical parameters from observed SSS spectra would be an atmosphere model that simulates the radiation transport processes. However, observed SSS high-resolution grating spectra reveal highly complex details that cast doubts on the feasibility of achieving unique results from atmosphere modeling. In this article, I discuss two independent atmosphere model analyses of the same data set, leading to different results. I then show some of the details that complicate the analysis and conclude that we need to approach the interpretation of high-resolution SSS spectra differently. We need to focus more on the data than the models and to use more phenomenological approaches as is traditionally done with optical spectra., Comment: Accepted in JASR. 7 pages, 6 figure

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission is steadily progressing both in terms of system studies and technology developments. The mission is currently in Phase B1 and is maturing towards a successful mission adoption. This paper describes the mission status including the main accomplishments achieved during this phase in terms of convergence of system and technological aspects. An overview of the different system studies is given including the latest programmatic assumptions, emphasizing on the Mirror Assembly demonstration and the critical interfaces between the mirror and the different facilities that are being developed in tandem to the mission. The reference telescope design is also described based on the Silicon Pore Optics (SPO) technology. The main design choices are explained as well as the modelling performed to ensure that all technological and system level constraints are met from plate level all the way to the mirror assembly level. The resulting effective area performance and budgeting is briefly described and future improvements are identified.

We analyze here four observations of nova KT Eri (Nova Eri 2009) done with the Chandra High-Resolution Camera Spectrometer (HRC-S) and the Low-Energy Transmission Grating (LETG) in 2010, from day 71 until day 159 after the optical maximum, in the luminous supersoft X-ray phase. The spectrum presents many absorption features with a large range of velocity, from a few hundred km s−1 to 3100 km s−1 in the same observation, and a few prominent emission features, generally redshifted by more than 2000 km s−1. Although the uncertainty on the distance and the WD luminosity from the approximate fit do not let us rule out a larger absolute luminosity than our best estimate of ≃5 × 1037 erg s−1, it is likely that we observed only up to ≃40 per cent of the surface of the white dwarf, which may have been partially hidden by clumpy ejecta. Our fit with atmospheric models indicates a massive white dwarf in the 1.15–1.25 M⊙ range. A thermal spectrum originating in the ejecta appears to be superimposed on the white dwarf spectrum. It is complex, has more than one component, and may be due to a mixture of photoionized and shock-ionized outflowing material. We confirm that the ≃35-s oscillation that was reported earlier was detected in the last observation done on day 159 of the outburst.

Peaking at 3.7 mag on 2020 July 11, YZ Ret was the second-brightest nova of the decade. The nova's moderate proximity (2.7 kpc from Gaia) provided an opportunity to explore its multi-wavelength properties in great detail. Here we report on YZ Ret as part of a long-term project to identify the physical mechanisms responsible for high-energy emission in classical novae. We use simultaneous Fermi/LAT and NuSTAR observations complemented by XMM-Newton X-ray grating spectroscopy to probe the physical parameters of the shocked ejecta and the nova-hosting white dwarf. The XMM-Newton observations revealed a super-soft X-ray emission which is dominated by emission lines of CV, CVI, NVI, NVII, and OVIII rather than a blackbody-like continuum, suggesting CO-composition of the white dwarf in a high-inclination binary system. Fermi/LAT detected YZ Ret for 15 days with the gamma-ray spectrum best described by a power law with an exponential cut-off at 1.9 +/-0.6 GeV. In stark contrast with theoretical predictions and in keeping with previous NuSTAR observations of Fermi-detected classical novae (V5855 Sgr and V906 Car), the 3.5-78 keV X-ray emission is found to be two orders of magnitude fainter than the GeV emission. The X-ray emission observed by NuSTAR is consistent with a single-temperature thermal plasma. We detect no non-thermal tail of the GeV emission expected to extend down to the NuSTAR band. NuSTAR observations continue to challenge theories of high-energy emission from shocks in novae., 22 pages, 5 figures, 4 tables; accepted to MNRAS

Ultraluminous X-ray sources (ULXs) are mainly powered by accretion in neutron stars or stellar-mass black holes. Accreting at rates exceeding the Eddington limit by factors of a few up to hundreds, radiation pressure is expected to inflate the accretion disc, and drive fast winds that have in fact been observed at significant fractions of the speed of light. Given the super-Eddington luminosity, the accretion disc will be thicker than in sub-Eddington accretors such as common active galactic nuclei and X-ray binaries, leading to a different spectral energy distribution and, possibly, a different thermal status of the wind. Here we show the first attempt to calculate the photoionization balance of the winds driven by strong radiation pressure in thick discs with a focus on ULXs hosting black holes or non-magnetic neutron stars. We find that the winds are generally in thermally stable equilibrium, but long-term variations in the accretion rate and the inclination due to precession may have significant effects on the wind appearance and stability. Our model trends can explain the observed correlation between the spectral residuals around 1 keV and the ULX spectral state. We also find a possible correlation between the spectral hardness of the ULX, the wind velocity and the ionization parameter in support of the general scenario., Comment: 17 pages, 9 figures, 5 tables, accepted for publication in MNRAS

International audience; Within the solar system, X-ray emissions have been detected from every planet except the Ice Giants: Uranus and Neptune. We analyze the three archival Chandra X-ray observations of Uranus (each 24–30 ks duration) to date: a stand-alone Advanced CCD Imaging Spectrometer (ACIS) observation on August 7, 2002 and two High Resolution Camera (HRC) observations on November 11 and 12, 2017 coordinated with optical observations. For the earlier ACIS observation, the Uranus-coincident photons were clustered in the 0.6–1.1 keV spectral range, consistent with emission from Jupiter and Saturn. To test the significance of the detected signal, we distributed a grid of ∼10,000 Uranus-sized regions across the field of view (FoV). The number of Uranus-coincident X-ray photons in the 0.5–1.2 keV range exceeded 99.9% of Uranus-sized regions across the FoV (10.2 standard deviations > FoV mean; probability of chance occurrence ∼10−6–10−7). However, the planetary signal was low with only 5 ± 2.2 X-ray photons against a FoV mean background of 0.16 photons. Without the possibility of energy filtering, the recent HRC observations had a much brighter background (FoV mean ∼10 photons). Consequently, neither of the new observations provided a second unambiguous Uranus detection, although a 40-min interval of brightening on November 12, 2017 did produce a signal above 99.9% of the FoV. The observed Uranus X-ray fluxes of 10−15–10−16 erg/cm2/s are consistent with previous observational limits and modeling predictions. These fluxes exceed expectations from scattered solar emission alone, suggesting either a larger X-ray albedo than Jupiter/Saturn or the possibility of additional X-ray production processes at Uranus. Further observations are needed to test this.

The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory (ESA/INTEGRAL) was launched aboard a Proton-DM2 rocket on 17 October 2002 at 06:41 CEST, from Baikonur in Kazakhstan. Since then, INTEGRAL has been providing long, uninterrupted observations (up to about 47h, or 170ksec, per satellite orbit of 2.7 days) with a large field-of-view (FOV, fully coded: 100 deg), millisecond time resolution, keV energy resolution, polarization measurements, as well as additional wavelength coverage at optical wavelengths. This is realized by two main instruments in the 15keV to 10MeV energy range, the spectrometer SPI (spectral resolution 3keV at 1.8MeV) and the imager IBIS (angular resolution: 12arcmin FWHM), complemented by X-ray (JEM-X; 3–35keV) and optical (OMC; Johnson V-band) monitor instruments. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments, built to reduce the background, are also very efficient all-sky γ-ray detectors, which provide virtually omni-directional monitoring above ∼75keV. Besides the long, scheduled observations, INTEGRAL can rapidly (within a couple of hours) re-point and conduct Target of Opportunity (ToO) observations on a large variety of sources. INTEGRAL observations and their scientific results have been building an impressive legacy: The discovery of currently more than 600 new high-energy sources; the first-ever direct detection of Ni and Co radio-active decay lines from a Type Ia supernova; spectroscopy of isotopes from galactic nucleo-synthesis sources; new insights on enigmatic positron annihilation in the Galactic bulge and disk; and pioneering gamma-ray polarization studies. INTEGRAL is also a successful actor in the new multi-messenger astronomy introduced by non-electromagnetic signals from gravitational waves and from neutrinos: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. Up to now more than 1750 scientific papers based on INTEGRAL data have been published in refereed journals. In this paper, we will give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment., Kuulkers, Erik, et al., he OMC team has been funded by different Spanish grants, including Spanish State Research Agency grants PID2019–107061GB–C61 and MDM–2017-0737 (Unidad de Excelencia María de Maeztu – CAB). The INTEGRAL French teams acknowledge partial funding from the French Space Agency (CNES). The Danish JEM-X gratefully acknowledges support from the Danish PRODEX delegation through contract C90057. The INTEGRAL Italian team acknowledges support form the Italian Space Agency, ASI, along these years via different agreements, last of which is 2019–35-HH.0. LH acknowledges support from SFI under grant 19/FFP/6777 and the EU AHEAD2020 project (grant agreement 871158). MH acknowledges support from Spanish MICINN grant PID2019-108709GB-I00. TS is supported by the German Research Society (DFG-Forschungsstipendium SI 2502/1-1 & SI 2502/3-1).

We examine four high resolution reflection grating spectrometers (RGS) spectra of the February 2009 outburst of the luminous recurrent nova LMC 2009a. They were very complex and rich in intricate absorption and emission features. The continuum was consistent with a dominant component originating in the atmosphere of a shell burning white dwarf (WD) with peak effective temperature between 810,000 K and a million K, and mass in the 1.2-1.4 M$_\odot$ range. A moderate blue shift of the absorption features of a few hundred km s$^{-1}$ can be explained with a residual nova wind depleting the WD surface at a rate of about 10$^{-8}$ M$_\odot$ yr$^{-1}$. The emission spectrum seems to be due to both photoionization and shock ionization in the ejecta. The supersoft X-ray flux was irregularly variable on time scales of hours, with decreasing amplitude of the variability. We find that both the period and the amplitude of another, already known 33.3 s modulation, varied within timescales of hours. We compared N LMC 2009a with other Magellanic Clouds novae, including 4 serendipitously discovered as supersoft X-ray sources (SSS) among 13 observed within 16 years after the eruption. The new detected targets were much less luminous than expected: we suggest that they were partially obscured by the accretion disk. Lack of SSS detections in the Magellanic Clouds novae more than 5.5 years after the eruption constrains the average duration of the nuclear burning phase., Comment: Accepted for publication in MNRAS

In 1979, the Voyager spacecraft arrived at Jupiter. Amongst their rich array of discoveries, they identified bright bursts of radio emission at kHz frequencies1, often called quasi-periodic (QP) bursts, and discovered Jupiter’s ultraviolet (UV) aurora2 - the most powerful aurora in the Solar System3. The same year that the Voyager spacecraft explored the Jovian system, the Einstein X-ray Observatory took the first X-ray images of Jupiter4 and discovered that planets can also produce bright and dynamic X-ray aurora5,6. Over the subsequent decades, these distinct multi-waveband emissions have all been observed to pulse with quasi-periodic regularity7–10. Here, we combine simultaneous observations by the Juno spacecraft with the X-ray and UV observatories: XMM-Newton, Chandra and the Hubble Space Telescope. These observations show that the radio, UV and X-ray pulses are all synchronised, beating in time together. Further, they reveal that the X-ray and radio pulses share an identical 42.5 minute periodicity with simultaneously measured compression-mode Ultra Low Frequency (ULF) waves in Jupiter’s outer magnetosphere11. ULF waves are known to modulate wave-particle interactions that can cause electron and ion precipitation, providing a physically consistent explanation for the observed simultaneous ion and electron emissions. The unification of Jupiter’s X-ray, UV and radio pulsations and their connection to ULF waves provides fundamental and potentially universal insights into the redistribution of energy in magnetised space environments.

Within the solar system, X-ray emissions have been detected from every planet except the Ice Giants: Uranus and Neptune. Here, we present three Chandra X-ray Observations of Uranus (each 24-30 ks duration): an Advanced CCD Imaging Spectrometer (ACIS) observation during solar maximum on 7 August 2002 and two High Resolution Camera (HRC) observations during solar minimum on 11 and 12 November 2017. The ACIS observation from 2002 shows a low signal but statistically significant detection of X-rays from Uranus. The measured Uranus X-ray fluxes of 10-15-10-16 erg/cm2/s from this detection are consistent with upper limits and modelling predictions in previous work (Ness & Schmidt. 2000; Cravens et al. 2006). The photon energy distribution from this observation is consistent with an X-ray emission from charge exchange or scattering of solar photons, as observed for Jupiter and Saturn. The two HRC observations from 2017 constitute non-detections. For 11 Nov 2017, the X-ray emission coincident with Uranus’ location is dimmer than 98% of the Field of View. 12 November 2017, was also a non-detection, but with tentative hints of planetary X-ray signatures: Uranus was 4 times brighter than the previous day, and brighter than 94% of the Field of View (1.6 standard deviations > Field of View mean). At this time, the Uranus coincident X-ray signature also exhibited timing variation distinct from the field of view. Further and longer observations will be required to better characterise the nature of the X-ray emissions from Uranus.

Jupiter’s unique x-ray aurora is driven by the same processes as Earth’s: Heavy ion scattering by electromagnetic waves., Jupiter’s rapidly rotating, strong magnetic field provides a natural laboratory that is key to understanding the dynamics of high-energy plasmas. Spectacular auroral x-ray flares are diagnostic of the most energetic processes governing magnetospheres but seemingly unique to Jupiter. Since their discovery 40 years ago, the processes that produce Jupiter’s x-ray flares have remained unknown. Here, we report simultaneous in situ satellite and space-based telescope observations that reveal the processes that produce Jupiter’s x-ray flares, showing surprising similarities to terrestrial ion aurora. Planetary-scale electromagnetic waves are observed to modulate electromagnetic ion cyclotron waves, periodically causing heavy ions to precipitate and produce Jupiter’s x-ray pulses. Our findings show that ion aurorae share common mechanisms across planetary systems, despite temporal, spatial, and energetic scales varying by orders of magnitude.

The 2007-2009 solar minimum was the longest of the space age. We present the first of two companion papers on Chandra and XMM-Newton X-ray campaigns of Jupiter through February-March 2007. We find that low solar X-ray flux during solar minimum causes Jupiter's equatorial regions to be exceptionally X-ray dim (0.21 GW at minimum; 0.76 GW at maximum). While the Jovian equatorial emission varies with solar cycle, the aurorae have comparably bright intervals at solar minimum and maximum. We apply atomic charge exchange models to auroral spectra and find that iogenic plasma of sulphur and oxygen ions provides excellent fits for XMM-Newton observations. The fitted spectral S:O ratios of 0.4-1.3 are in good agreement with in situ magnetospheric S:O measurements of 0.3-1.5, suggesting that the ions that produce Jupiter's X-ray aurora predominantly originate inside the magnetosphere. The aurorae were particularly bright on 24-25 February and 8-9 March, but these two observations exhibit very different spatial, spectral, and temporal behavior; 24-25 February was the only observation in this campaign with significant hard X-ray bremsstrahlung from precipitating electrons, suggesting this may be rare. For 8-9 March, a bremsstrahlung component was absent, but bright oxygen O(6+)lines and best-fit models containing carbon, point to contributions from solar wind ions. This contribution is absent in the other observations. Comparing simultaneous Chandra ACIS and XMM-Newton EPIC spectra showed that ACIS systematically underreported 0.45- to 0.6-keV Jovian emission, suggesting quenching may be less important for Jupiter's atmosphere than previously thought. We therefore recommend XMM-Newton for spectral analyses and quantifying opacity/quenching effects.

All X-ray light curves of nova V4743 Sgr (2002), taken during and after outburst, contain a 0.75 mHz periodic signal that can most plausibly be interpreted as being excited by the rotation of the white dwarf in an intermediate polar system. This interpretation faces the challenge of an apparent multi-frequency nature of this signal in the light curves taken days 180 and 196 after outburst. We show that the multi-sine fit method, based on a superposition of two sine functions, yields two inherently indistinguishable solutions, i.e. the presence of two close frequencies, or a single signal with constant frequency but variable modulation amplitude. Using a power spectrum time map, we show that on day 180, a reduction of the modulation amplitude of the signal coincides with a substantial overall flux decline while on day 196, the signal was only present during the first half of the observation. Supported by simulations, we show that such variations in amplitude can lead to false beating that manifests itself as a multiple signal if computing a periodogram over the full light curve. Therefore, the previously proposed double frequency nature of both light curves was probably an artefact while we consider a single signal with frequency equal to the white dwarf rotation as more plausible., 8 pages, 8 figures, 2 tables, Accepted for publication in MNRAS

Two long AstroSat Soft X-ray Telescope observations were taken of the third recorded outburst of the Symbiotic Recurrent Nova, V3890 Sgr. The first observing run, 8.1-9.9 days after the outburst, initially showed a stable intensity level with a hard X-ray spectrum that we attribute to shocks between the nova ejecta and the pre-existing stellar companion. On day 8.57, the first, weak, signs appeared of Super Soft Source (SSS) emission powered by residual burning on the surface of the White Dwarf. The SSS emission was observed to be highly variable on time scales of hours. After day 8.9, the SSS component was more stable and brighter. In the second observing run, on days 15.9-19.6 after the outburst, the SSS component was even brighter but still highly variable. The SSS emission was observed to fade significantly during days 16.8-17.8 followed by re-brightening. Meanwhile the shock component was stable leading to increase in hardness ratio during the period of fading. AstroSat and XMM-Newton observations have been used to study the spectral properties of V3890 Sgr to draw quantitative conclusions even if their drawback is model-dependence. We used the xspec to fit spectral models of plasma emission, and the best fits are consistent with the elemental abundances being lower during the second observing run compared to the first for spectra >1 keV. The SSS emission is well fit by non-local thermal equilibrium model atmosphere used for white dwarfs. The resulting spectral parameters, however, are subject to systematic uncertainties such as completeness of atomic data., 15 pages, 10 figures, Accepted for publication in the Monthly Notices of the Royal Astronomical Society

The recurrent nova (RN) V3890 Sgr was observed during the 7th day after the onset of its most recent outburst, with the Chandra ACIS-S camera and High Energy Transmission Gratings (HETG). A rich emission line spectrum was detected, due to transitions of Fe-L and K-shell ions ranging from neon to iron. The measured absorbed flux is $\approx 10^{-10}$ erg cm$^{-2}$ s$^{-1}$ in the 1.4-15 Angstrom range (0.77-8.86 keV). The line profiles are asymmetric, blue-shifted and skewed towards the blue side, as if the ejecta moving towards us are less absorbed than the receding ones. The full width at half maximum of most emission lines is 1000-1200 km s$^{-1}$, with some extended blue wings. The spectrum is thermal and consistent with a plasma in collisional ionization equilibrium with column density 1.3 $\times 10^{22}$ cm$^{-2}$ and at least two components at temperatures of about 1 keV and 4 keV, possibly a forward and a reverse shock, or regions with differently mixed ejecta and red giant wind. The spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we cannot distinguish whether the shocks occurred at a distance of few AU from the red giant, or near the giant's photosphere, in a high density medium containing only a small mass. The ratios of the flux in lines of aluminum, magnesium and neon relative to the flux in lines of silicon and iron probably indicate a carbon-oxygen white dwarf (CO WD)., In press on the ApJ

Shocks in gamma-ray emitting classical novae are expected to produce bright thermal and non-thermal X-rays. We test this prediction with simultaneous NuSTAR and Fermi/LAT observations of nova V906 Car, which exhibited the brightest GeV gamma-ray emission to date. The nova is detected in hard X-rays while it is still gamma-ray bright, but contrary to simple theoretical expectations, the detected 3.5-78 keV emission of V906 Car is much weaker than the simultaneously observed >100 MeV emission. No non-thermal X-ray emission is detected, and our deep limits imply that the gamma-rays are likely hadronic. After correcting for substantial absorption (N_H ~ 2 x 10^23 cm^-2), the thermal X-ray luminosity (from a 9 keV optically-thin plasma) is just ~2% of the gamma-ray luminosity. We consider possible explanations for the low thermal X-ray luminosity, including the X-rays being suppressed by corrugated, radiative shock fronts or the X-rays from the gamma-ray producing shock are hidden behind an even larger absorbing column (N_H >10^25 cm^-2). Adding XMM-Newton and Swift/XRT observations to our analysis, we find that the evolution of the intrinsic X-ray absorption requires the nova shell to be expelled 24 days after the outburst onset. The X-ray spectra show that the ejecta are enhanced in nitrogen and oxygen, and the nova occurred on the surface of a CO-type white dwarf. We see no indication of a distinct super-soft phase in the X-ray lightcurve, which, after considering the absorption effects, may point to a low mass of the white dwarf hosting the nova., 19 pages, 6 figures, 7 tables; accepted to MNRAS

The magnetosphere sustained by the rotation of the Earth's liquid iron core traps charged particles, mostly electrons and protons, into structures referred to as the Van Allen belts. These radiation belts, in which the density of charged energetic particles can be very destructive for sensitive instrumentation, have to be crossed on every orbit of satellites traveling in elliptical orbits around the Earth, as is the case for ESA's INTEGRAL and XMM-Newton missions. This paper presents the first working version of the 5DRBM-e model, a global, data-driven model of the radiation belts for trapped electrons. The model is based on in-situ measurements of electrons by the radiation monitors on board the INTEGRAL and XMM-Newton satellites along their long elliptical orbits for respectively 16 and 19 years of operations. This model, in its present form, features the integral flux for trapped electrons within energies ranging from 0.7 to 1.75 MeV. Cross-validation of the 5DRBM-e with the well-known AE8min/max and AE9mean models for a low eccentricity GPS orbit shows excellent agreement, and demonstrates that the new model can be used to provide reliable predictions along widely different orbits around Earth for the purpose of designing, planning, and operating satellites with more accurate instrument safety margins. Future work will include extending the model based on electrons of different energies and proton radiation measurement data., 11 pages, 7 figures, 1 table

We analysed Kepler data of two similar dwarf novae V344 Lyr and V1504 Cyg in order to study optical fast stochastic variability (flickering) by searching for characteristic break frequencies in their power density spectra. Two different stages of activity were analysed separately, i.e. regular outbursts and quiescence. Both systems show similar behaviour during both activity stages. The quiescent power density spectra show a dominant low break frequency which is also present during outburst with a more or less stable value in V344 Lyr while it is slightly higher in V1504 Cyg. The origin of this variability is probably the whole accretion disc. Both outburst power density spectra show additional high frequency components which we interpret as generated by the rebuilt inner disc that was truncated during quiescence. Moreover, V344 Lyr shows the typical linear rms-flux relation which is strongly deformed by a possible negative superhump variability., 10 pages, 9 figures, 2 tables, Accepted for publication in MNRAS

We present a study of the C K-edge using high-resolution LETGS Chandra spectra of four novae during their super-soft-source (SSS) phase. We identified absorption lines due to C~ii K$\alpha$, C~iii K$\alpha$ and C~ iii K$\beta$ resonances. We used these astronomical observations to perform a benchmarking of the atomic data, which involves wavelength shifts of the resonances and photoionization cross-sections. We used improved atomic data to estimate the C~ii and C~iii column densities. The absence of physical shifts for the absorption lines, the consistence of the column densities between multiple observations and the high temperature required for the SSS nova atmosphere modeling support our conclusion about an ISM origin of the respective absorption lines. Assuming a collisional ionization equilibrium plasma the maximum temperature derived from the ratio of C~ii/C~iii column densities of the absorbers correspond to $T_{max}< 3.05\times10^{4}$ K., Comment: 7 pages, 7 figures

An optical light curve of SU UMa type dwarf nova V1504 Cyg taken by Kepler was analysed in order to study fast optical variability (flickering). We calculated power density spectra and rms–flux relations for two different stages of activity, i.e. quiescence and regular outbursts. A multicomponent power density spectrum with two break frequencies was found during both activity stages. The rms–flux relation is obvious only in the quiescent data. However, while the collection of all outburst data do not show this variability, every individual outburst does show it in the majority of cases keeping the rms value approximately in the same interval. Furthermore, the same analysis was performed for light-curve subsamples taken from the beginning, middle and the end of the supercycle both for quiescence and regular outbursts. Every light-curve subsample shows the same multicomponent power density spectrum. The stability of the break frequencies over the supercycle can be confirmed for all frequencies except for the high break frequency during outburst, which shows variability, but with rather low confidence. Finally, the low break frequency can be associated with the geometrically thin disc or its inner edge, while the high break frequency can originate from the inner geometrically thick hot disc. Furthermore, with our statistical method to simulate flickering light curves, we show that the outburst flickering light curve of V1504 Cyg needs an additional constant flux level to explain the observed rms–flux behaviour. Therefore, during the outbursts another non-turbulent radiation source should be present.

Nova SMC 2016 has been the most luminous nova known in the direction of the Magellanic Clouds. It turned into a very luminous supersoft X-ray source between day 16 and 28 after the optical maximum. We observed it with Chandra, the HRC-S camera and the Low Energy Transmission Grating (LETG) on 2016 November and 2017 January (days 39 and 88 after optical maximum), and with XMM-Newton on 2016 December (day 75). We detected the compact white dwarf (WD) spectrum as a luminous supersoft X-ray continuum with deep absorption features of carbon, nitrogen, magnesium, calcium, probably argon and sulfur on day 39, and oxygen, nitrogen and carbon on days 75 and 88. The spectral features attributed to the WD atmosphere are all blue-shifted, by about 1800 km/s on day 39 and up to 2100 km/s in the following observations. Spectral lines attributed to low ionization potential transitions in the interstellar medium are also observed. Assuming the distance of the Small Magellanic Cloud, the bolometric luminosity exceeded Eddington level for at least three months. A preliminary analysis with atmospheric models indicates effective temperature around 700,000 K on day 39, peaking at the later dates in the 850,000-900,000 K range, as expected for a 1.25 m(sol) WD. We suggest a possible classification as an oxygen-neon WD, but more precise modeling is needed to accurately determine the abundances. The X-ray light curves show large, aperiodic ux variability, not associated with spectral variability. We detected red noise, but did not find periodic or quasi-periodic modulations., Accepted for publication in the Astrophysical Journal, pending final editorial review after "minor changes"

The recurrent nova M31N 2008-12a experiences annual eruptions, contains a near-Chandrasekhar mass white dwarf, and has the largest mass accretion rate in any nova system. In this paper, we present Hubble Space Telescope (HST) WFC3/UVIS photometry of the late decline of the 2015 eruption. We couple these new data with archival HST observations of the quiescent system and Keck spectroscopy of the 2014 eruption. The late-time photometry reveals a rapid decline to a minimum luminosity state, before a possible recovery / re-brightening in the run-up to the next eruption. Comparison with accretion disk models supports the survival of the accretion disk during the eruptions, and uncovers a quiescent disk mass accretion rate of the order of $10^{-6}\,M_\odot\,\mathrm{yr}^{-1}$, which may rise beyond $10^{-5}\,M_\odot\,\mathrm{yr}^{-1}$ during the super-soft source phase - both of which could be problematic for a number of well-established nova eruption models. Such large accretion rates, close to the Eddington limit, might be expected to be accompanied by additional mass loss from the disk through a wind and even collimated outflows. The archival HST observations, combined with the disk modeling, provide the first constraints on the mass donor; $L_\mathrm{donor}=103^{+12}_{-11}\,L_\odot$, $R_\mathrm{donor}=14.14^{+0.46}_{-0.47}\,R_\odot$, and $T_\mathrm{eff, donor}=4890\pm110$ K, which may be consistent with an irradiated M31 red-clump star. Such a donor would require a system orbital period $\gtrsim5$ days. Our updated analysis predicts that the M31N 2008-12a WD could reach the Chandrasekhar mass in < 20 kyr., 20 pages, 8 figures, 5 tables, accepted for publication in The Astrophysical Journal

We assessed the scientific productivity of XMM-Newton by examining XMM-Newton publications and data usage statistics. We analyse 3272 refereed papers, published until the end of 2012, that directly use XMM-Newton data. The SAO/NASA Astrophysics Data System (ADS) was used to provide additional information on each paper including the number of citations. For each paper, the XMM-Newton observation identifiers and instruments used to provide the scientific results were determined. The identifiers were used to access the XMM-Newton Science Archive (XSA) to provide detailed information on the observations themselves and on the original proposals. The information obtained from these sources was then combined to allow the scientific productivity of the mission to be assessed. Since around three years after the launch of XMM-Newton there have been around 300 refereed papers per year that directly use XMM-Newton data. After more than 13 years in operation, this rate shows no evidence that it is decreasing. Since 2002, around 100 scientists per year become lead authors for the first time on a refereed paper which directly uses XMM-Newton data. Each refereed XMM-Newton paper receives around four citations per year in the first few years with a long-term citation rate of three citations per year, more than five years after publication. About half of the articles citing XMM-Newton articles are not primarily X-ray observational papers. The distribution of elapsed time between observations taken under the Guest Observer programme and first article peaks at 2 years with a possible second peak at 3.25 years. Observations taken under the Target of Opportunity programme are published significantly faster, after one year on average. The fraction of science time taken until the end of 2009 that has been used in at least one article is ∼90%. Most observations were used more than once, yielding on average a factor of two in usage on available observing time per year. About 20 % of all slew observations have been used in publications. The scientific productivity of XMM-Newton measured by the publication rate, number of new authors and citation rate, remains extremely high with no evidence that it is decreasing after more than 13 years of operations.

We analysed an X-ray light curve of the dwarf nova RU Peg taken by XMM-Newton with a duration of 46300 s. The power density spectrum has a complicated shape with two red noise and two white noise components, indicating the presence of two turbulent regions. We developed a statistical "toy model" to study light curves with variability produced by an unstable turbulent accretion flow from the inner disc. Our results are consistent with a disc truncation radius maximally 0.8 x 10^9 cm. We found that any fluctuation of the viscous mass accretion at the inner disc are visible as UV and X-ray variations with the same break frequency in the power density spectrum. This process is generating low frequency variability. A second break suggests the presence of a faster X-ray variability component which must be generated by another process likely localised between the inner disc and the white dwarf., accepted for publication in MNRAS, 12 pages, 8 figures, 1 table

We present spectral and timing analyses of simultaneous X-ray and UV observations of the VY Scl system MV Lyr taken by XMM-Newton, containing the longest continuous X-ray+UV light curve and highest signal-to-noise X-ray (EPIC) spectrum to date. The RGS spectrum displays emission lines plus continuum, confirming model approaches to be based on thermal plasma models. We test the sandwiched model based on fast variability that predicts a geometrically thick corona that surrounds an inner geometrically thin disc. The EPIC spectra are consistent with either a cooling flow model or a 2-T collisional plasma plus Fe emission lines in which the hotter component may be partially absorbed which would then originate in a central corona or a partially obscured boundary layer, respectively. The cooling flow model yields a lower mass accretion rate than expected during the bright state, suggesting an evaporated plasma with a low density, thus consistent with a corona. Timing analysis confirms the presence of a dominant break frequency around log(f/Hz) = -3 in the X-ray Power Density Spectrum (PDS) as in the optical PDS. The complex soft/hard X-ray light curve behaviour is consistent with a region close to the white dwarf where the hot component is generated. The soft component can be connected to an extended region. We find another break frequency around log(f/Hz) = -3.4 that is also detected by Kepler. We compared flares at different wavelengths and found that the peaks are simultaneous but the rise to maximum is delayed in X-rays with respect to UV., Comment: 17 pages, 21 figures, 4 tables, Accepted for publication in MNRAS

The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was observed on February 22 and 23 by the Chandra X-ray Observatory Transmission Grating Spectrometers. By that time the supersoft source phase had already ended and Chandra spectra are consistent with emission from a hot, shock-heated circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are more sharply peaked than expected for a spherically-symmetric blast wave, with a full width at zero intensity of approximately 2400 km/s, a full width at half maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s. The red wings of lines are increasingly absorbed toward longer wavelengths by material within the remnant. We conclude that the blast wave was sculpted by an aspherical circumstellar medium in which an equatorial density enhancement plays a role, as in earlier symbiotic nova explosions. Expansion of the dominant X-ray emitting material is aligned close to the plane of the sky and most consistent with an orbit seen close to face-on. Comparison of an analytical blast wave model with the X-ray spectra, Swift observations and near-infrared line widths indicates the explosion energy was approximately 10^43 erg, and confirms an ejected mass of approximately 10^-7 Msun. The total mass lost is an order of magnitude lower than the accreted mass required to have initiated the explosion, indicating the white dwarf is gaining mass and is a supernova Type 1a progenitor candidate., To appear in the Astrophysical Journal

We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions.

Emission line fluxes from cool stars are widely used to establish an apparent emission measure distribution, Emd-app(Te), between temperatures characteristic of the low transition region and the low corona. The true emission measure distribution, Emd-t(Te), is determined by the energy balance and geometry adopted and, with a numerical model, can be used to predict Emd-app(Te), to guide further modelling. The scaling laws that exist between coronal parameters arise from the dimensions of the terms in the energy balance equation. Here, analytical approximations to numerical solutions for Emd-t(Te) are presented, which show how the constants in the coronal scaling laws are determined. The apparent emission measure distributions show a minimum value at some temperature (T0) and a maximum at the mean coronal temperature Tc (although in some stars, emission from active regions can contribute). It is shown that, for the energy balance and geometry adopted, the analytical values of the emission measure and electron pressure at T0 and Tc, depend on only three parameters: the stellar surface gravity and the values of T0 and Tc. The results are tested against full numerical solutions for Epsilon Eri (K2 V) and are applied to Procyon (alpha CMi; F5 IV/V). The analytical approximations can be used to restrict the required range of full numerical solutions, to check the assumed geometry and to show where the adopted energy balance may not be appropriate.

We want to study whether the astrometric and photometric accuracies obtained for the Carte du Ciel plates digitized with a commercial digital camera are high enough for scientific exploitation of the plates. We use a digital camera Canon EOS~5Ds, with a 100mm macrolens for digitizing. We analyze six single-exposure plates and four triple-exposure plates from the Helsinki zone of Carte du Ciel (+39 degr < delta < 47 degr). Each plate is digitized using four images, with a significant central area being covered twice for quality control purposes. The astrometric calibration of the digitized images is done with the data from the Gaia TGAS (Tycho-Gaia Astrometric Solution) of the first Gaia data release (Gaia DR1), Tycho-2, HSOY (Hot Stuff for One Year), UCAC5 (USNO CCD Astrograph Catalog), and PMA catalogs. The best astrometric accuracy is obtained with the UCAC5 reference stars. The astrometric accuracy for single-exposure plates is sigma(R.A.)=0.16" and sigma(Dec.)=0.15" expressed as a Gaussian deviation of the astrometric residuals. For triple-exposure plates the astrometric accuracy is sigma(R.A.)=0.12" and sigma(Dec.)=0.13". The 1-sigma uncertainty of photometric calibration is about 0.28 mag and 0.24 mag for single- and triple-exposure plates, respectively. We detect the photographic adjacency (Kostinsky) effect in the triple-exposure plates. We show that accuracies at least of the level of scanning machines can be achieved with a digital camera, without any corrections for possible distortions caused by our instrumental setup. This method can be used to rapidly and inexpensively digitize and calibrate old photographic plates enabling their scientific exploitation., Accepted for publication in Astronomy & Astrophysics

CSS081007:030559+054715 was discovered by the Catalina Real-time Transient Survey. Optical spectroscopy revealed a multi-peaked Hα emission line profile with radial velocities exceeding 1500 km/s, as well as strong Ne emission, suggestive of a neon nova. We monitored the source extensively with the Swift satellite, obtaining a unique dataset spanning 270 days in the soft X-ray and UV bands. The data reveal a soft, blackbody-like spectrum with a temperature around 55 eV (though dependent on the modelling), variable X-ray and UV light curves with a 1.77 day period in both the X-ray and UV bands, a longer timescale modulation of ∼ 50 days, followed by a slowly declining trend in the soft X-ray and UV flux. We highlight the Swift observations and their implications for the SSS nature of this object (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Aims: The launch of Swift has allowed many more novae to be observed regularly over the X-ray band. Such X-ray observations of novae can reveal ejecta shocks and the nuclear burning white dwarf, allowing estimates to be made of the ejecta velocity. Methods: We analyse XMM-Newton and Swift X-ray and UV observations of the nova V598 Pup, which was initially discovered in the XMM-Newton slew survey. These data were obtained between 147 and 255 days after the nova outburst, and are compared with the earlier, brighter slew detection. Results: The X-ray spectrum consists of a super-soft source, with the soft emission becoming hotter and much fainter between days ~147 and ~172 after the outburst, and a more slowly declining optically thin component, formed by shocks with kT ~ 200-800 eV (corresponding to velocities of 400-800 km s^-1). The main super-soft phase had a duration of less than 130 days. The Reflection Grating Spectrometer data show evidence of emission lines consistent with optically thin emission of kT ~100 eV and place a limit on the density of the surrounding medium of log(n_e/cm^-3) < 10.4 at the 90 % level. The UV emission is variable over short timescales and fades by at least one magnitude (at lambda ~ 2246-2600 angstrom) between days 169 and 255., 6 pages, 5 figures, accepted for publication in A&A

The evolution of the 2006 outburst of the recurrent nova RS Ophiuchi was followed with 12 X-ray grating observations with Chandra and XMM-Newton. We present detailed spectral analyses using two independent approaches. From the best dataset, taken on day 13.8 after outburst, we reconstruct the temperature distribution and derive elemental abundances. We find evidence for at least two distinct temperature components on day 13.8 and a reduction of temperature with time. The X-ray flux decreases as a power-law, and the power-law index changes from -5/3 to -8/3 around day 70 after outburst. This can be explained by different decay mechanisms for the hot and cool components. The decay of the hot component and the decrease in temperature are consistent with radiative cooling, while the decay of the cool component can be explained by the expansion of the ejecta. We find overabundances of N and of alpha-elements, which could either represent the composition of the secondary that provides the accreted material or that of the ejecta. The N overabundance indicates CNO-cycled material. From comparisons to abundances for the secondary taken from the literature, we conclude that 20-40% of the observed nitrogen could originate from the outburst. The overabundance of the alpha-elements is not typical for stars of the spectral type of the secondary in the RS Oph system, and white dwarf material might have been mixed into the ejecta. However, no direct measurements of the alpha-elements in the secondary are available, and the continuous accretion may have changed the observable surface composition., Comment: 24 pages, 15 figures, 7 tables

Chandra HETG observations of RS Ophiuchi at day 13.9 of the 2006 outburst reveal a rich spectrum of emission lines from abundant ions formed over a wide temperature range (∼ 3 × 10 6 to 60 × 10 6 K) indicative of shock heating of the circumstellar medium by the expanding blast wave. Lines are asymmetric and strongly broadened (v ∼ 2400 km s −1 at zero intensity). Using simple analytical model profiles, we show how the lines are shaped by differential absorption in the red giant wind and explosion ejecta, and that shock heating to multimillion degree temperatures appears to have occurred preferentially in the direction perpendicular to the line of sight. We conclude that the asymmetric nature of the offset 1/r 2 density profile and likely equatorial circumstellar density enhancement in which the explosion occurred are responsible for both the shock collimation and broad range in plasma temperature observed. The ejecta mass deduced from X-ray absorption is more easily reconciled with the expected mass accretion rate for material enhanced in metals by up to an order of magnitude.

We present analyses of observations of epsilon Eridani (K2 V) made with the Low Energy Transmission Grating Spectrometer on Chandra and the Extreme Ultraviolet Explorer, supplemented by observations made with the Space Telescope Imaging Spectrograph, the Far Ultraviolet Spectroscopic Explorer and the Reflection Grating Spectrometer on XMM-Newton. The observed emission lines are used to find relative element abundances, to place limits on the electron densities and pressures and to determine the mean apparent emission measure distribution. As in the previous paper by Sim & Jordan (2003a), the mean emitting area as a function of the electron temperature is derived by comparisons with a theoretical emission measure distribution found from energy balance arguments. The final model has a coronal temperature of 3.4 x 10^6 K, an electron pressure of 1.3 x 10^16 cm^-3 K at T_e = 2 x 10^5 K and an area filling factor of 0.14 at 3.2 x 10^5 K. We discuss a number of issues concerning the atomic data currently available. Our analyses are based mainly on the latest version of CHIANTI (v5.2). We conclude that the Ne/O relative abundance is 0.30, larger than that recommended from solar studies, and that there is no convincing evidence for enhanced coronal abundances of elements with low first ionization potentials.

We find that the classical nova V723 Cas (1995) is still an active X-ray source more than 12 years after outburst and analyze seven X-ray observations carried out with Swift between 2006 January 31 and 2007 December 3. The average count rate is 0.022+/-0.01 cts s^-1 but the source is variable within a factor of two of the mean and does not show any signs of turning off. We present supporting optical observations which show that between 2001 and 2006 an underlying hot source was present with steadily increasing temperature. In order to confirm that the X-ray emission is from V723 Cas, we extract a ROSAT observation taken in 1990 and find that there was no X-ray source at the position of the nova. The Swift XRT spectra resemble those of the Super Soft X-ray binary Sources (SSS) which is confirmed by RXTE survey data which show no X-ray emission above 2 keV between 1996 and 2007. Using blackbody fits we constrain the effective temperature to between T_eff=(2.8-3.8)x10^5 K and a bolometric luminosity >5x10^36 erg s^-1 and caution that luminosities from blackbodies are generally overestimated and temperatures underestimated. We discuss a number of possible explanations for the continuing X-ray activity, including the intriguing possibility of steady hydrogen burning due to renewed accretion., Accepted by AJ; 7 pages, 5 figures, 2 tables

The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed twice with Chandra and once with XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after outburst. We confirm a 35-sec period on day 54.0 and found that it originates from the SSS emission and not from the shock. We discus the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionization of oxygen. The absorption component has average velocities of -1286+-267 km/s on day 39.7 and of -771+-65 km/s on day 66.9. The wavelengths of the emission line components are consistent with their rest wavelengths as confirmed by measurements of non-self absorbed He-like intersystem lines. We have evidence that these lines originate from the shock rather than the outer layers of the outflow and may be photoexcited in addition to collisional excitations. We found collisionally excited emission lines that are fading at wavelengths shorter than 15A that originate from the radiatively cooling shock. On day 39.5 we find a systematic blue shift of -526+-114 km/s from these lines. We found anomalous He-like f/i ratios which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000sec. This can be explained by photoionization of neutral oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}., Comment: 16 pages, 10 figures, 4 tables. Accepted by ApJ; v2: Co-author Woodward added

We present infrared spectroscopy of the recurrent nova RS Ophiuchi, obtained 11.81, 20.75 and 55.71 days following its 2006 eruption. The spectra are dominated by hydrogen recombination lines, together with HeI, OI and OII lines; the electron temperature of ~10^4 K implied by the recombination spectrum suggests that we are seeing primarily the wind of the red giant, ionized by the ultraviolet flash when RS Oph erupted. However, strong coronal emission lines (i.e. emission from fine structure transitions in ions having high ionization potential) are present in the last spectrum. These imply a temperature of 930000K for the coronal gas; this is in line with x-ray observations of the 2006 eruption. The emission line widths decrease with time in a way that is consistent with the shock model for the x-ray emission., 5 pages, 4 figures, 3 tables. Accepted for publication in MNRAS

V745 Sco is a recurrent nova, with the most recent eruption occurring in February 2014. V745 Sco was first observed by Swift a mere 3.7 hr after the announcement of the optical discovery, with the super-soft X-ray emission being detected around four days later and lasting for only ~two days, making it both the fastest follow-up of a nova by Swift and the earliest switch-on of super-soft emission yet detected. Such an early switch-on time suggests a combination of a very high velocity outflow and low ejected mass and, together with the high effective temperature reached by the super-soft emission, a high mass white dwarf (>1.3 M_sun). The X-ray spectral evolution was followed from an early epoch where shocked emission was evident, through the entirety of the super-soft phase, showing evolving column density, emission lines, absorption edges and thermal continuum temperature. UV grism data were also obtained throughout the super-soft interval, with the spectra showing mainly emission lines from lower ionization transitions and the Balmer continuum in emission. V745 Sco is compared with both V2491 Cyg (another nova with a very short super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet discovered). The longer recurrence time compared to M31N 2008-12a could be due to a lower mass accretion rate, although inclination of the system may also play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft source phase yet discovered, providing a detailed and informative dataset for study., 14 pages, 11 figures (4 in colour), accepted for publication in MNRAS

The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia Supernova progenitor candidate. Following the 2013 eruption, a campaign was initiated to detect the predicted 2014 eruption and to then perform high cadence optical photometric and spectroscopic monitoring using ground-based telescopes, along with rapid UV and X-ray follow-up with the Swift satellite. Here we report the results of a high cadence multicolour optical monitoring campaign, the spectroscopic evolution, and the UV photometry. We also discuss tantalising evidence of a potentially related, vastly-extended, nebulosity. The 2014 eruption was discovered, before optical maximum, on October 2, 2014. We find that the optical properties of M31N 2008-12a evolve faster than all Galactic recurrent novae known, and all its eruptions show remarkable similarity both photometrically and spectroscopically. Optical spectra were obtained as early as 0.26 days post maximum, and again confirm the nova nature of the eruption. A significant deceleration of the inferred ejecta expansion velocity is observed which may be caused by interaction of the ejecta with surrounding material, possibly a red giant wind. We find a low ejected mass and low ejection velocity, which are consistent with high mass-accretion rate, high mass white dwarf, and short recurrence time models of novae. We encourage additional observations, especially around the predicted time of the next eruption, towards the end of 2015., 23 pages, 11 figures, 5 tables, accepted for publication in Astronomy & Astrophysics

We present Chandra HETGS observations of the classical T Tauri star (CTTS) V4046 Sgr. The He-like triplets of O VII, Ne IX, and Si XIII are clearly detected. Similar to the CTTS TW Hya and BP Tau, the forbidden lines of O VII and Ne IX are weak compared to the intercombination line, indicating high plasma densities in the X-ray emitting regions. The Si XIII triplet, however, is within the low-density limit, in agreement with the predictions of the accretion funnel infall model with an additional stellar corona. V4046 Sgr is the first close binary exhibiting these features. Together with previous high-resolution X-ray data on TW Hya and BP Tau, and in contrast to T Tau, now three out of four CTTS show evidence of accretion funnels.

X-ray emission from cool stars is an important tracer for stellar activity. The X-ray luminosity reflects different levels of activity and covers four orders of magnitude in stars of spectral types M-F. Low spectral resolution provided by X-ray observations of stellar coronae in the past allowed the determination of temperature distributions and elemental abundances making use of atomic databases (listing line emissivities and bremsstrahlung continuum for a given temperature structure). The new missions XMM-Newton and Chandra carry X-ray gratings providing sufficient spectral resolution to measure the fluxes of strategic emission lines. I describe the different approaches applicable to low-resolution and high-resolution spectra, especially focusing on the new grating spectra with X-ray lines. From only a few lines it is possible to determine plasma temperatures and associated densities, to check for any effects from resonant scattering, and to identify particular abundance anomalies. Line-based temperature- and density measurements represent only a fraction of the total plasma, but the pressure environment of different fractions can be probed simply by selection of specific lines. Selected results are presented covering all aspects of line-based analyses., Comment: 11 pages, 2 figures; Advances in Space Research, Proceedings for COSPAR meeting in Paris July 2004

β Pictoris (HR 2020) is the most prominent prototype of stars with circumstellar disks and has generated particular interest in the framework of young planetary systems. Given its spectral type A5, stellar activity is not expected. Nevertheless, resonance lines of C  and O  typical for a chromosphere and transition region have been unambiguously detected with FUSE. We present results from an XMM-Newton observation of β Pic and find evidence for X-ray emission. In particular, we detected an emission of O  at 21.6 A with the MOS detectors. These findings present a challenge for the development of both stellar activity and disk models. We discuss and investigate various models to explain the observed emission including the presence of a cool corona and a boundary layer.

(abridged) We investigate the long-term evolution of X-ray coronae of solar analogs based on high-resolution X-ray spectroscopy and photometry with XMM-Newton. Six nearby main-sequence G stars with ages between ~0.1 Gyr and \~1.6 Gyr and rotation periods between ~1d and 12.4d have been observed. We derive coronal element abundances and the coronal emission measure distribution (EMD). The abundances change from an inverse-First Ionization Potential (FIP) distribution in stars with ages around 0.1 Gyr to a solar-type FIP distribution in stars at ages of 0.3 Gyr and beyond. The coronal EMDs show shapes characterized by power-laws on each side of the EMD peak. The latter shifts from temperatures of about 10 MK in the most rapidly rotating, young stars to temperatures around 4 MK in the oldest target considered here. The power-law index on the cooler side of the EMD exceeds expected slopes for static loops, with typical values being 1.5-3. We interpret this slope with a model in which the coronal emission is due to a superposition of stochastically occurring flares, with an occurrence rate that is distributed in radiated energy E as a power-law, dN/dE ~ E^-a. Our EMDs indicate a ~ 2.2-2.8, in excellent agreement with values previously derived from light curves of magnetically active stars. We derive the range of flare energies required to explain the light-curve modulation. In an overall scenario, we propose that flaring activity plays a larger role in more active stars. In this model, the higher flare rate is responsible both for the higher average coronal temperature and the high coronal X-ray luminosity, two parameters that are indeed found to be correlated., Comment: 35 pages, 14 figures, 10 tables

We present an XMM-Newton analysis of the cataclysmic variable T Leo. The X-ray light curve shows sinusoidal variation on a period P_x equal to 0.89^{+0.14}_{-0.10} times the previously spectroscopically determined orbital period. Furthermore, we find a signal in the power spectrum at 414 sec that could be attributed to the spin period of the white dwarf. If true, T Leo would be the first confirmed superoutbursting intermediate polar IP). The spin profile is double-peaked with a peak separation of about 1/3 spin phases. This appears to be a typical feature for IPs with a small magnetic field and fast white dwarf rotation. An alternative explanation is that the 414 sec signal is a Quasi-periodic Oscillation (QPO) that is caused by mass transfer variation from the secondary, a bright region (``blob'') rotating in the disc at a radius of approximately ~9 Rwd or - more likely - a travelling wave close to the inner disc edge of a dwarf nova with a low field white dwarf. The XMM-Newton RGS spectra reveal double peaked emission for the O VIII Ly alpha line. Scenarios in the IP and dwarf nova model are discussed (an emitting ring in the disc, bright X-ray spot on disc edge, or emitting accretion funnels), but the intermediate polar model is favoured. Supported is this idea by the finding that only the red peak appears to be shifted and the `blue' peak is compatible with the rest wavelength. The red peak thus is caused by emission from the northern accretion spot when it faces the observer. Instead, the peak at the rest wavelength is caused when the southern accretion funnel is visible just on the lower edge of the white dwarf - with the velocity of the accreting material being perpendicular to the line of sight., Comment: 11 pages, 15 figures, accepted by A&A