An XMM-Newton proton response matrix

Soft protons constitute an important source of background in focusing X-ray telescopes, as Chandra and XMM-Newton experience has shown. The optics in fact transmit them to the focal plane with efficiency similar to the X-ray photon one. This effect is a good opportunity to study the environment of the Earth magnetosphere crossed by the X-ray satellite orbits, provided that we can link the spectra detected by the instruments with the ones impacting on the optics. For X-ray photons this link has the form of the so-called response matrix that includes the optics effective area and the energy redistribution in the detectors. Here we present a first attempt to produce a proton response matrix exploiting ray-tracing and GEANT4 simulations with the final aim to be able to analyse XMM-Newton soft proton data and link them to the external environment. If the procedure is found to be reliable, it can be applied to any future X-ray missions to predict the soft particles spectra impacting on the focal plane instruments.     

A systematic analysis of the XMM-Newton background: IV

We show the results obtained in the FP7 European program EXTraS and in the ESA R&D ATHENA activity AREMBES aimed at a deeper understanding of the XMM-Newton background to better design the ATHENA mission. Thanks to an analysis of the full EPIC archive coupled to the information obtained by the Radiation Monitor we show the cosmic ray origin of the unfocused particle background and its anti-correlation with the solar activity. We show the first results of the effort to obtain informations about the particle component of the soft proton focused background.     

First XMM-Newton observations of strongly magnetic cataclysmic variables – I. Spectral studies of DP Leo and WW Hor

We present an analysis of the X-ray spectra of two strongly magnetic cataclysmic variables, DP Leo and WW Hor, made using XMM-Newton . Both systems were in intermediate levels of accretion. Hard optically thin X-ray emission from the shocked accreting gas was detected from both systems, while a soft blackbody X-ray component from the heated surface was detected only in DP Leo. We suggest that the lack of a soft X-ray component in WW Hor is owing to the fact that the accretion area is larger than in previous observations with a resulting lower temperature for the re-processed hard X-rays. Using a multi-temperature model of the post-shock flow, we estimate that the white dwarf in both systems has a mass greater than 1 M_⊙. The implications of this result are discussed. We demonstrate that the 'soft X-ray excess' observed in many magnetic cataclysmic variables can be partially attributed to using an inappropriate model for the hard X-ray emission.     

Diffuse thermal X-ray emission in the core of the young massive cluster Westerlund 1

We present an analysis of the diffuse hard X-ray emission in the core of the young massive Galactic cluster Westerlund 1 based on a 48 ks XMM-Newton observation. Chandra results for the diffuse X-ray emission have indicated a soft thermal component together with a hard component that could be either thermal or non-thermal. We seek to resolve this ambiguity regarding the hard component exploiting the higher sensitivity of XMM-Newton to diffuse emission. Our new X-ray spectra from the central (2′ radius) diffuse emission are found to exhibit He-like Fe 6.7 keV line emission, demonstrating that the hard emission in the cluster core is predominantly thermal in origin. Potential sources of this hard component are reviewed, namely an unresolved Pre-Main Sequence population, a thermalized cluster wind and Supernova Remnants interacting with stellar winds. We find that the thermalized cluster wind likely contributes the majority of the hard emission with some contribution from the Pre-Main Sequence population. It is unlikely that Supernova Remnants are contributing significantly to the Westerlund 1 diffuse emission at the current epoch.     

Soft proton flux on <Emphasis Type="Italic">ATHENA</Emphasis> focal plane and its impact on the magnetic diverter design

The experience gained with the current generation of X-ray telescopes like Chandra and XMM-Newton has shown that low energy “soft” protons can pose a severe threat to the possibility to exploit scientific data, reducing the available exposure times by up to 50% and introducing a poorly reproducible background component. These soft protons are present in orbits outside the radiation belts and enter the mirrors, being concentrated towards the focal plane instruments, losing energy along their path and finally depositing their remaining energy in the detectors. Their contribution to the residual background will be even higher for ATHENA with respect to previous missions, given the much higher collecting area of the mirrors, even if the instruments will likely suffer no significant radiation damage from this particles flux. As a consequence this soft proton flux shall be damped with the use of a magnetic diverter to avoid excess background loading on the WFI or X-IFU instruments. We present here a first complete evaluation of this background component for the two focal plane instruments of the ATHENA mission in absence of a magnetic diverter, and derive the requirements for such device to reduce the soft protons induced background below the level required to enable the mission science. We estimate the soft proton flux expected in L2 for the interplanetary component and for the component generated locally by acceleration processes in the magnetotail. We produce a proton response matrix for each of the two instruments of ATHENA focal plane, exploiting two independent Monte Carlo simulations to estimate the optics concentration efficiency, and Geant4 simulations to evaluate the energy loss inside the radiation filters and deposited in the detector. With this modular approach we derive the expected fluxes and spectra for the soft protons component of the background. Finally, we calculate the specifics of a magnetic diverter able to reduce such flux below the required level for both X-IFU and WFI.     

The X—ray Background from the Warm Gas of the Galactic Halo

LETTERS1 INTRODUCTIONIn the hierarchical scenario of structure formation, massive dark ha1os fOrm by gravitationalaggregation of individual low-mass objects, whi1e the stel1ar disks of spiral galaxies like theMilky Way form by accretion of gas which cools and falls onto the galaxies from an extendedsurrounding reservoir. FOr a massive galaxy of M ~ 10"MO, the surrounding gas can be heatedto temperature of T ~ 106 K by gravitational1y-driven shocks, the dominant cooling is thus dueto …     

UV and X-ray variability of the narrow-line Seyfert 1 galaxy Ark 564

We analyze eight XMM-Newton observations of the bright Narrow Line Seyfert 1 galaxy Arakelian 564(Ark 564). These observations, separated bye~6 days, allow us to look for correlations between the simultaneous ultraviolet(UV) emission(from th Optical Monitor) with not only the X-ray flux but also with different X-ray spectral parameters. The X-ray spectra from all the observations are found to be adequately fitted by a double Comptonization model where the soft excess and the hard X-ray power law are represented by thermal Comptonization in a low temperature plasma and hot corona, respectively. Apart from the fluxes of each component, the hard X-ray power law index is found to be variable. These results suggest that the variability is associated with changes in the geometry of the inner region. The UV emission is found to be variable and well correlated with the high energy index while the correlations with the fluxes of each component are found to be weaker. Using viscous timescale arguments we rule out the possibility that the UV variation is due to the fluctuating accretion rate in the outer disk. If the UV variation is driven by X-ray reprocessing, then our results indicate that the strength of the X-ray reprocessing depends more on the geometry of the X-ray producing inner region rather than on the X-ray luminosity alone.     

Geant4 simulations of soft proton scattering in X-ray optics

Low energy protons (< 300 keV) can enter the field of view of X-ray telescopes, scatter on their mirror surfaces at small incident angles, and deposit energy on the detector. This phenomenon can cause intense background flares at the focal plane decreasing the mission observing time (e.g. the XMM-Newton mission) or in the most extreme cases, damaging the X-ray detector. A correct modelization of the physics process responsible for the grazing angle scattering processes is mandatory to evaluate the impact of such events on the performance (e.g. observation time, sensitivity) of future X-ray telescopes as the ESA ATHENA mission. The Remizovich model describes particles reflected by solids at glancing angles in terms of the Boltzmann transport equation using the diffuse approximation and the model of continuous slowing down in energy. For the first time this solution, in the approximation of no energy losses, is implemented, verified, and qualitatively validated on top of the Geant4 release 10.2, with the possibility to add a constant energy loss to each interaction. This implementation is verified by comparing the simulated proton distribution to both the theoretical probability distribution and with independent ray-tracing simulations. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering. At 250 keV multiple scattering delivers large proton angles and it is not consistent with the observation. Among the tested models, the single scattering seems to better reproduce the scattering efficiency at the three energies but energy loss obtained at small scattering angles is significantly lower than the experimental values. In general, the energy losses obtained in the experiment are higher than what obtained by the simulation. The experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes because of the lack of measurements at low energies (< 200 keV) and small reflection angles, so we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies are available, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.     

The anatomy of a magnetar: XMM monitoring of the transient anomalous X-ray pulsar XTE J1810–197

We present the latest results from a multi-epoch timing and spectral study of the Transient Anomalous X-ray Pulsar XTE J1810–197. We have acquired seven observations of this pulsar with the Newton X-ray Multi-mirror Mission (XMM-Newton) over the course of two and a half years, to follow the spectral evolution as the source fades from outburst. The spectrum is arguably best characterized by a two-temperature blackbody whose luminosities are decreasing exponentially with τ ₁=870 d and τ ₂=280 d, respectively. The temperatures of these components are currently cooling at a rate of 22% per year from a nearly constant value recorded at earlier epochs of kT ₁=0.25 keV and kT ₂=0.67 keV, respectively. The new data show that the temperature T ₁ and luminosity of that component have nearly returned to their historic quiescent levels and that its pulsed fraction, which has steadily decreased with time, is now consistent with the previous lack of detected pulsations in quiescence. We also summarize the detections of radio emission from XTE J1810–197, the first confirmed for any AXP. We consider possible models for the emission geometry and mechanisms of XTE J1810–197. XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This research is supported by XMM-Newton grant NNG05GJ61G and NASA ADP grant ADP04-0059-0024.     

X-ray observations of PSR B0355+54 and its pulsar wind nebula

We present X-ray data of the middle-aged radio pulsar PSR B0355+54. The XMM-Newton and Chandra observations show not only emission from the pulsar itself, but also compact diffuse emission extending ∼50″ in the opposite direction to the pulsar’s proper motion. Our analysis also indicates the presence of fainter diffuse emission extending ∼5′ from the point source. The morphology of the diffuse component is similar to the ram-pressure confined pulsar wind nebulae detected for other sources. We find that the compact diffuse component is well-fitted with a power-law, with an index that is consistent with the values found for other pulsar wind nebulae. The core emission from the pulsar can be characterized with a thermal plus power-law fit, with the thermal emission most likely originating in a hot polar cap.     

A new interpretation of the remarkable X-ray spectrum of the symbiotic star CH Cyg

We have re-analysed the ASCA X-ray spectrum of the bright symbiotic star CH Cyg, which exhibits apparently distinct hard and soft X-ray components. Our analysis demonstrates that the soft X-ray emission can be interpreted as scattering of the hard X-ray component in a photoionized medium surrounding the white dwarf. This is in contrast to previous analyses in which the soft X-ray emission was fitted separately and assumed to arise independently of the hard X-ray component. We note the striking similarity between the X-ray spectra of CH Cyg and Seyfert 2 galaxies, which are also believed to exhibit scattering in a photoionized medium.     

How the X-ray spectrum of a narrow-line Seyfert 1 galaxy may be reflection-dominated

A model for the inner regions of accretion flows is presented where, owing to disc instabilities, cold and dense material is clumped into deep sheets or rings. Surrounding these density enhancements is hot, tenuous gas where coronal dissipation processes occur. We expect this situation to be most relevant when the accretion rate is close to Eddington and the disc is radiation-pressure-dominated, and so may apply to narrow-line Seyfert 1 (NLS1) galaxies. In this scenario, the hard X-ray source is obscured for most observers, and so the detected X-ray emission would be dominated by reflection off the walls of the sheets. A simple Comptonization calculation shows that the large photon-indices characteristic of NLS1s would be a natural outcome of two reprocessors closely surrounding the hard X-ray source. We test this model by fitting the XMM-Newton spectrum of the NLS1 1H  0707–495  between 0.5 and 11 keV with reflection-dominated ionized disc models. A very good fit is found with three different reflectors each subject to the same  Γ=2.35  power law. An iron overabundance is still required to fit the sharp drop in the spectrum at around 7 keV. We note that even a small corrugation of the accretion disc may result in  Γ>2  and a strong reflection component in the observed spectrum. Therefore, this model may also explain the strength and the variability characteristics of the MCG–6-30-15 Fe K α line. The idea needs to be tested with further broad-band XMM-Newton observations of NLS1s.     

Solar Energetic Particle Events in the 23rd Solar Cycle: Interplanetary Magnetic Field Configuration and Statistical Relationship with Flares and CMEs

We study the influence of the large-scale interplanetary magnetic field configuration on the solar energetic particles (SEPs) as detected at different satellites near Earth and on the correlation of their peak intensities with the parent solar activity. We selected SEP events associated with X- and M-class flares at western longitudes, in order to ensure good magnetic connection to Earth. These events were classified into two categories according to the global interplanetary magnetic field (IMF) configuration present during the SEP propagation to 1 AU: standard solar wind or interplanetary coronal mass ejections (ICMEs). Our analysis shows that around 20 % of all particle events are detected when the spacecraft is immersed in an ICME. The correlation of the peak particle intensity with the projected speed of the SEP-associated coronal mass ejection is similar in the two IMF categories of proton and electron events, ≈?0.6. The SEP events within ICMEs show stronger correlation between the peak proton intensity and the soft X-ray flux of the associated solar flare, with correlation coefficient r=0.67±0.13, compared to the SEP events propagating in the standard solar wind, r=0.36±0.13. The difference is more pronounced for near-relativistic electrons. The main reason for the different correlation behavior seems to be the larger spread of the flare longitude in the SEP sample detected in the solar wind as compared to SEP events within ICMEs. We discuss to what extent observational bias, different physical processes (particle injection, transport, etc.), and the IMF configuration can influence the relationship between SEPs and coronal activity.     

Soft X-ray oscillations from AT Mic: Flare plasma diagnostics

We consider the flare oscillations from the active red dwarf AT Mic detected with the XMM-Newton space observatory in the soft X-ray energy range (0.2–12 keV). Following Mitra-Kraev et al. (2005a), we associate the observed oscillations with a period of ≈750 s with the excitation of a standing slow magnetoacoustic (SMA) wave in a coronal loop. The damping of flare loop SMA oscillations is shown to be governed by electron thermal conduction. We have estimated the plasma density (≈3 × 10¹⁰ cm^?3) and the minimum magnetic field strength (≈100 G) in the region of flare energy release. The adopted model is consistent with the results of a spectral analysis of the soft X-ray emission. The piston mechanism is assumed to be responsible for the excitation of loop SMA oscillations.     

Determination of the magnetic fields of Magellanic X-ray pulsars

The 80 high-mass X-ray binary(HMXB) pulsars that are known to reside in the Magellanic Clouds(MCs) have been observed by the XMM-Newton and Chandra X-ray telescopes on a regular basis for 15 years,and the XMM-Newton and Chandra archives contain nearly complete information about the duty cycles of the sources with spin periods P_S 100 s.We have reprocessed the archival data from both observatories and we combined the output products with all the published observations of 31 MC pulsars with P_S 100 s in an attempt to investigate the faintest X-ray emission states of these objects that occur when accretion to the polar caps proceeds at the smallest possible rates.These states determine the so-called propeller lines of the accreting pulsars and yield information about the magnitudes of their surface magnetic fields.We have found that the faintest states of the pulsars segregate into five discrete groups which obey to a high degree of accuracy the theoretical relation between spin period and X-ray luminosity.So the entire population of these pulsars can be described by just five propeller lines and the five corresponding magnetic moments(0.29,0.53,1.2,2.9 and 7.3,in units of 10~(30) G cm~3).     

A brief description of observational results from the supersoft X-ray detector aboard Shenzhou-2

Observational results from the supersoft X-ray detector (SD) aboard the spacecraft Shenzhou-2 are briefly described. The resultspertain to cosmic γ-ray bursts solar x-ray bursts, high-energy charged particles and soft X-ray background radiation. The detector is a proportional counter with a polypropylene thin-film window of 50 mm diameter, it operates in the energy range 0.23–3.0keV covered by six energy channels. Two grades of time resolution are used: 40 ms for recording burst events and 520 ms when there is no triggering signal resulted from a burst event. Figures 1 and 2 show the light curves and energy spectra of two cosmic γ-ray bursts (starting time 2001 Jan 17, 09:37:25.21 UT and 2001 Mar 9, 12:33:55.692 UT), and Figures 3 and 4, the results on two solar X-ray burst (2001 Apr 6, 19:14:09.11 UT, and 2001 May 20, 06:02:12.58 UT). The detector records the ambient high-energy charged particles when there is no burst event and the shutter of the window is closed. 110 data sets of high-energy charged particles along the spacecraft orbit have been collected. As examples, the variations of the particle counting rate along the orbit are shown in Figs. 6a, 6b, 8e, 8f and 7. More than 10 events of particle precipitation induced by solar proton events have also been recorded, some of which are displayed in Figs.6c–6f and 7. Some of the data of soft X-ray background radiation shown in Fig. 8 were obtained when the shutter was open, and they are important for the data processing of the burst events.     

X-Ray Spectral Study of AGN Sources Content in Some Deep Extragalactic XMM-Newton Fields

We undertake a spectral study of a sample of bright X-ray sources taken from six XMM-Newton fields at high galactic latitudes, where AGN are the most populous class. These six fields were chosen such that the observation had an exposure time more than 60 ksec, had data from the EPIC-pn detector in the full-Frame mode and lying at high galactic latitude |b|>25^∘. The analysis started by fitting the spectra of all sources with an absorbed power-law model, and then we fitted all the spectra with an absorbed power-law with a low energy black-body component model.The sources for which we added a black body gave an F-test probability of 0.01 or less (i.e. at 99% confidence level), were recognized as sources that display soft excess. We perform a comparative analysis of soft excess spectral parameters with respect to the underlying power-law one for sources that satisfy this criterion. Those sources, that do not show evidence for a soft excess, based on the F-test probability at a 99% confidence level, were also fitted with the absorbed power-law with a low energy black-body component model with the black-body temperature fixed at 0.1 and 0.2 keV. We establish upper limits on the soft excess flux for those sources at these two temperatures. Finally we have made use of Aladdin interactive sky atlas and matching with NASA/IPAC Extragalactic Database (NED) to identify the X-ray sources in our sample. For those sources which are identified in the NED catalogue, we make a comparative study of the soft excess phenomenon for different types of systems.     

Neutron star surface emission: Beyond the dipole model

Recent Chandra and XMM-Newton observations of a number of X-ray “dim” pulsating neutron stars revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ～8–35% in amplitude), the pulse shape is often non-sinusoidal, and the hard X-ray color appears to be anti-correlated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4-3125, has been found to undergo rather sensible changes both in its spectral and timing properties over a timescale of a few years. By modeling the light curves of two sources, RBS 1223 and RX J0720.4-3125, it has been found evidence for two hot regions located at a slightly non antipodal direction. All these new findings are difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field. Here we present more realistic models of surface emission, where the effects of different neutron star thermal and magnetic surface distributions are accounted for. We show how a star-centered field made of a dipolar and a quadrupolar component can influence the properties of the observed light curves and we present results that account self-consistently for toroidal and poloidal crustal field configurations.     

The particle background of the <Emphasis Type="Italic">X-IFU</Emphasis> instrument

In this paper we are going to review the latest estimates for the particle background expected on the X-IFU instrument onboard of the ATHENA mission. The particle background is induced by two different particle populations: the so called “soft protons” and the Cosmic rays. The first component is composed of low energy particles (< 100s keV) that get funnelled by the mirrors towards the focal plane, losing part of their energy inside the filters and inducing background counts inside the instrument sensitivity band. The latter component is induced by high energy particles (> 100 MeV) that possess enough energy to cross the spacecraft and reach the detector from any direction, depositing a small fraction of their energy inside the instrument. Both these components are estimated using Monte Carlo simulations and the latest results are presented here.     

An XMM-Newton observation of the extreme narrow-line Seyfert 1 galaxy Mrk 359

We present XMM-Newton observations of Mrk 359, the first narrow-line Seyfert 1 galaxy (NLS1) discovered. Even among NLS1s, Mrk 359 is an extreme case with extraordinarily narrow optical emission lines. The XMM-Newton data show that Mrk 359 has a significant soft X-ray excess which displays only weak absorption and emission features. The     continuum, including reflection, is flatter than that of the typical NLS1, with     . A strong emission line of equivalent width ≈200 eV is also observed, centred near 6.4 keV. We fit this emission with two line components of approximately equal strength: a broad iron line from an accretion disc and a narrow, unresolved core. The unresolved line core has an equivalent width of ≈120 eV and is consistent with fluorescence from neutral iron in distant reprocessing gas, possibly in the form of a 'molecular torus'. Comparison of the narrow-line strengths in Mrk 359 and other low–moderate luminosity Seyfert 1 galaxies with those in QSOs suggests that the solid angle subtended by the distant reprocessing gas decreases with increasing active galactic nucleus luminosity.