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The Advanced Telescope for High-energy Astrophysics (Athena+) is being proposed to ESA as the L2 mission (for a launch in 2028) and is specifically designed to answer two of the most pressing questions for astrophysics in the forthcoming decade: How did ordinary matter assemble into the large scale structures we see today? and how do black holes grow and shape the Universe? For addressing these two issues, Athena+ will provide transformational capabilities in terms of angular resolution, effective area, spectral resolution, grasp, that will make it the most powerful X-ray observatory ever flown. Such an observatory, when opened to the astronomical community, will be used for virtually all classes of astrophysical objects, from high-z gamma-ray bursts to the closest planets in our solar neighborhood. In this paper, we briefly review the core science objectives of Athena+, present the science requirements and the foreseen implementation of the mission, and illustrate its transformational capabilities compared to existing facilities.

The centre of our Galaxy harbours a 4 million solar mass black hole that is unusually quiet: its present X-ray luminosity is more than 10 orders of magnitude less than its Eddington luminosity. The observation of iron fluorescence and hard X-ray emission from some of the massive molecular clouds surrounding the Galactic Centre has been interpreted as an echo of a past flare. Alternatively, low-energy cosmic rays propagating inside the clouds might account for the observed emission, through inverse bremsstrahlung of low energy ions or bremsstrahlung emission of low energy electrons. Here we report the observation of a clear decay of the hard X-ray emission from the molecular cloud Sgr B2 during the past 7 years thanks to more than 20 Ms of INTEGRAL exposure. The measured decay time is compatible with the light crossing time of the molecular cloud core . Such a short timescale rules out inverse bremsstrahlung by cosmic-ray ions as the origin of the X ray emission. We also obtained 2-100 keV broadband X-ray spectra by combining INTEGRAL and XMM-Newton data and compared them with detailed models of X-ray emission due to irradiation of molecular gas by (i) low-energy cosmic-ray electrons and (ii) hard X-rays. Both models can reproduce the data equally well, but the time variability constraints and the huge cosmic ray electron luminosity required to explain the observed hard X-ray emission strongly favor the scenario in which the diffuse emission of Sgr B2 is scattered and reprocessed radiation emitted in the past by Sgr A*. Using recent parallax measurements that place Sgr B2 in front of Sgr A*, we find that the period of intense activity of Sgr A* ended between 75 and 155 years ago., Comment: Accepted for publication in ApJ. 10 pages, 5 figures

Recent Suzaku X-ray observations of the ejecta-dominated supernova remnant W49B have shown that in the global spectrum there is a clear indication for the presence of overionized plasma whose physical origin is still under debate. In order to ascertain the physical origin of such a rapidly cooling plasma, we focus on the study of its spatial localization within the X-ray emitting ejecta. We confirm the presence of a saw-edged excess (interpreted as a strong radiative recombination continuum) in the global spectrum above 8 keV, emerging above the ionization-equilibrium model. We produce a hardness ratio map to determine where the plasma is overionized and we perform a spectral analysis of the regions with and without strong overionization. We find that the overionized plasma is localized in the center of the remnant and in its western jet, while it is not detected in the bright eastern jet, where the expansion of the ejecta is hampered by their interaction with a dense interstellar cloud. The location of overionized plasma suggests that the inner ejecta are rapidly cooling by expansion, unlike the outer ejecta, for which expansion is hampered by interstellar clouds seen in H2, Comment: Accepted for publication as a Letter in Astronomy and Astrophysics.

Context: The Rayleigh-Taylor instabilities generated by the deceleration of a supernova remnant during the ejecta-dominated phase are known to produce finger-like structures in the matter distribution which modify the geometry of the remnant. The morphology of supernova remnants is also expected to be modified when efficient particle acceleration occurs at their shocks. Aims: The impact of the Rayleigh-Taylor instabilities from the ejecta-dominated to the Sedov-Taylor phase is investigated over one octant of the supernova remnant. We also study the effect of efficient particle acceleration at the forward shock on the growth of the Rayleigh-Taylor instabilities. Methods: We modified the Adaptive Mesh Refinement code RAMSES to study with hydrodynamic numerical simulations the evolution of supernova remnants in the framework of an expanding reference frame. The adiabatic index of a relativistic gas between the forward shock and the contact discontinuity mimics the presence of accelerated particles. Results: The great advantage of the super-comoving coordinate system adopted here is that it minimizes numerical diffusion at the contact discontinuity, since it is stationary with respect to the grid. We propose an accurate expression for the growth of the Rayleigh-Taylor structures that connects smoothly the early growth to the asymptotic self-similar behaviour. Conclusions: The development of the Rayleigh-Taylor structures is affected, although not drastically, if the blast wave is dominated by cosmic rays. The amount of ejecta that makes it into the shocked interstellar medium is smaller in the latter case. If acceleration occurs at both shocks the extent of the Rayleigh-Taylor structures is similar but the reverse shock is strongly perturbed., Comment: 15 pages, 12 figures, accepted for publication in Astronomy and Astrophysics with minor editorial changes. Version with full resolution images can be found at http://www.lpl.arizona.edu/~ffrasche/~12692.pdf

The medium-lived 44Ti isotope is synthesised by explosive Si-burning in core-collapse supernovae. It is extremely sensitive to the dynamics of the explosion and therefore can be used to indirectly probe the explosion scenario. The young supernova remnant Cassiopeia A is to date the only source of gamma-ray lines from 44Ti decay. The emission flux has been measured by CGRO/COMPTEL, BeppoSAX/PDS and INTEGRAL/IBIS. The high-resolution spectrometer SPI on-board the INTEGRAL satellite can provide spectrometric information about the emission. The line profiles reflect the kinematics of the 44Ti in Cassiopeia A and can thus place constraints on its nucleosynthesis and potentially on the associated explosion process. Using 4 years of data from INTEGRAL/SPI, we have searched for the gamma-ray signatures from the decay of the 44Ti isotope. The overwhelming instrumental background noise required an accurate modelling and a solid assessment of the systematic errors in the analysis. Due to the strong variability of the instrumental background noise, it has not been possible to extract the two lines at 67.9 and 78.4keV. Regarding the high-energy line at 1157.0keV, no significant signal is seen in the 1140-1170keV band, thereby suggesting that the line signal from Cassiopeia A is broadened by the Doppler effect. From our spectrum, we derive a ~ 500km/s lower limit at 2sigma on the expansion velocity of the 44Ti ejecta. Our result does not allow us to constrain the location of 44Ti since the velocities involved throughout the remnant, derived from optical and X-ray studies, are all far above our lower limit., Comment: 7 pages, 8 figures, published in A&A

Context. The Rayleigh-Taylor instabilities that are generated by the deceleration of a supernova remnant during the ejecta-dominated phase are known to produce finger-like structures in the matter distribution that modify the geometry of the remnant. The morphology of supernova remnants is also expected to be modified when efficient particle acceleration occurs at their shocks. Aims: The impact of the Rayleigh-Taylor instabilities from the ejecta-dominated to the Sedov-Taylor phase is investigated over one octant of the supernova remnant. We also study the effect of efficient particle acceleration at the forward shock on the growth of the Rayleigh-Taylor instabilities. Methods: We modified the Adaptive Mesh Refinement code RAMSES to study with hydrodynamic numerical simulations the evolution of supernova remnants in the framework of an expanding reference frame. The adiabatic index of a relativistic gas between the forward shock and the contact discontinuity mimics the presence of accelerated particles. Results: The great advantage of the super-comoving coordinate system adopted here is that it minimizes numerical diffusion at the contact discontinuity, since it is stationary with respect to the grid. We propose an accurate expression for the growth of the Rayleigh-Taylor structures that smoothly connects the early growth to the asymptotic self-similar behaviour. Conclusions: The development of the Rayleigh-Taylor structures is affected, although not drastically, if the blast wave is dominated by cosmic rays. The amount of ejecta that reaches the shocked interstellar medium is smaller in this case. If acceleration were to occur at both shocks, the extent of the Rayleigh-Taylor structures would be similar but the reverse shock would be strongly perturbed.

If a sizeable fraction of the energy of supernova remnant shocks is channeled into energetic particles (commonly identified with Galactic cosmic rays), then the morphological evolution of the remnants must be distinctly modified. Evidence of such modifications has been recently obtained with the Chandra and XMM-Newton X-ray satellites. To investigate these effects, we coupled a semi-analytical kinetic model of shock acceleration with a 3D hydrodynamic code (by means of an effective adiabatic index). This enables us to study the time-dependent compression of the region between the forward and reverse shocks due to the back reaction of accelerated particles, concomitantly with the development of the Rayleigh-Taylor hydrodynamic instability at the contact discontinuity. Density profiles depend critically on the injection level eta of particles: for eta up to about 10^-4 modifications are weak and progressive, for eta of the order of 10^-3 modifications are strong and immediate. Nevertheless, the extension of the Rayleigh-Taylor unstable region does not depend on the injection rate. A first comparison of our simulations with observations of Tycho's remnant strengthens the case for efficient acceleration of protons at the forward shock., Comment: accepted for publication in A&A (final version)

The supernova remnant (SNR) RX J1713.7-3946 (also known as G347.3-0.5) is part of the class of remnants dominated by synchrotron emission in X-rays. It is also one of the few shell-type SNRs observed at TeV energies allowing to investigate particle acceleration at SNRs shock. Our goal is to compare spatial and spectral properties of the remnant in X- and gamma-rays to understand the nature of the TeV emission. This requires to study the remnant at the same spatial scale at both energies. To complement the non-thermal spectrum of the remnant, we attempt to provide a reliable estimate for the radio flux density. In radio, we revisited ATCA data and used HI and mid-infrared observations to disentangle the thermal from the non-thermal emission. In X-rays, we produced a new mosaic of the remnant and degraded the spatial resolution of the X-ray data to the resolution of the HESS instrument to perform spatially resolved spectroscopy at the same spatial scale in X- and gamma-rays. Radial profiles were obtained to investigate the extension of the emission at both energies. We found that part of the radio emission within the SNR contours is thermal in nature. Taking this into account, we provide new lower and upper limits for the integrated synchrotron flux of the remnant at 1.4 GHz of 22 Jy and 26 Jy respectively. In X-rays, we obtained the first full coverage of RX J1713.7-3946 with XMM-Newton. The spatial variation of the photon index seen at small scale in X-rays is smeared out at HESS resolution. A non-linear correlation between the X- and gamma-ray fluxes of the type Fx \propto Fg^2.41 is found., Comment: 13 pages, 10 figures, accepted for publication in A&A. An image of the remnant with higher definition will be distributed through the XMM-Newton image gallery (http://xmm.esac.esa.int/external/xmm_science/gallery/public/)

We have conducted a radio study at 3.6, 6 and 20 cm using ATCA and VLA and reprocessed XMM-Newton and Chandra data of the pulsar wind nebula (PWN) in the supernova remnant (SNR) G0.9+0.1. The new observations revealed that the morphology and symmetry suggested by Chandra observations (torus and jet-like features) are basically preserved in the radio range in spite of the rich structure observed in the radio emission of this PWN, including several arcs, bright knots, extensions and filaments. The reprocessed X-ray images show for the first time that the X-ray plasma fills almost the same volume as the radio PWN. Notably the X-ray maximum does not coincide with the radio maximum and the neutron star candidate CXOU J174722.8-280915 lies within a small depression in the radio emission. From the new radio data we have refined the flux density estimates, obtaining S(PWN) ~ 1.57 Jy, almost constant between 3.6 and 20 cm. For the whole SNR (compact core and shell), a flux density S(at 20 cm)= 11.5 Jy was estimated. Based on the new and the existing 90 cm flux density estimates, we derived alpha(PWN)=-0.18+/-0.04 and alpha(shell)=-0.68+/- 0.07. From the combination of the radio data with X-ray data, a spectral break is found near nu ~ 2.4 x 10^(12) Hz. The total radio PWN luminosity is L(radio)=1.2 x 10^(35) erg s^(-1) when a distance of 8.5 kpc is adopted. By assuming equipartition between particle and magnetic energies, we estimate a nebular magnetic field B = 56 muG. The associated particle energy turns out to be U(part)=5 x 10^(47) erg and the magnetic energy U(mag)=2 x 10^(47) erg. Based on an empirical relation between X-ray luminosity and pulsar energy loss rate, and the comparison with the calculated total energy, a lower limit of 1100 yr is derived for the age of this PWN., Comment: 10 pages,8 figures, accepted for publication in A&A, June 13 2008

Important results achieved over the last years on supernova remnants, planetary nebulae and superbubbles are briefly reviewed in the context of X-ray observations. I intend to review the important open scientific questions in these fields, and the specific contributions that can be made by XMM-Newton., Comment: 4 pages, 1 figure, invited review for "XMM-Newton: The next decade", AN in press

A review of the main issues in the field of particle acceleration in Supernova Remnants is provided in the context of future X-ray observations with Simbol-X. After a summary of the nonthermal acceleration mechanisms at work, I briefly review the observations of supernova remnants in hard X-rays and in gamma rays. Open issues are discussed in this framework., Comment: 6 pages, 3 figures, invited talk at 'Simbol-X: the hard X-ray universe in focus', Bologna (Italy), 14-16 May, 2007. To appear in Memorie della SAIt

Simbol-X is a French-Italian mission, with a participation of German laboratories, for X-ray astronomy in the wide 0.5-80 keV band. Taking advantage of emerging technology in mirror manufacturing and spacecraft formation flying, Simbol-X will push grazing incidence imaging up to ~80 keV, providing an improvement of roughly three orders of magnitude in sensitivity and angular resolution compared to all instruments that have operated so far above 10 keV. This will open a new window in X-ray astronomy, allowing breakthrough studies on black hole physics and census and particle acceleration mechanisms. We describe briefly the main scientific goals of the Simbol-X mission, giving a few examples aimed at highlighting key issues of the Simbol-X design., Comment: Proc. of the workshop "Simbol-X: The hard X-ray universe in focus", Bologna 14-16 May, 2007

We use the Chandra X-ray Observatory to study the region in the Tycho supernova remnant between the blast wave and the shocked ejecta interface or contact discontinuity. This zone contains all the history of the shock-heated gas and cosmic-ray acceleration in the remnant. We present for the first time evidence for significant spatial variations of the X-ray synchrotron emission in the form of spectral steepening from a photon index of 2.6 right at the blast wave to a value of 3.0 several arcseconds behind. We interpret this result along with the profiles of radio and X-ray intensity using a self-similar hydrodynamical model including cosmic ray backreaction that accounts for the observed ratio of radii between the blast wave and contact discontinuity. Two different assumptions were made about the post-shock magnetic field evolution: one where the magnetic field (amplified at the shock) is simply carried by the plasma flow and remains relatively high in the post-shock region [synchrotron losses limited rim case], and another where the amplified magnetic field is rapidly damped behind the blast wave [magnetic damping case]. Both cases fairly well describe the X-ray data, however both fail to explain the observed radio profile. The projected synchrotron emission leaves little room for the presence of thermal emission from the shocked ambient medium. This can only be explained if the pre-shock ambient medium density in the vicinity of the Tycho supernova remnant is below 0.6 cm-3., Comment: Accepted for publication in ApJ - 61 pages, 17 figures

In the framework of the study of supernova remnants and their complex interaction with the interstellar medium and the circumstellar material, we focus on the galactic supernova remnant W49B. Its morphology exhibits an X-ray bright elongated nebula, terminated on its eastern end by a sharp perpendicular structure aligned with the radio shell. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca, and Fe. There is a variation of the temperature in the remnant with the highest temperature found in the eastern side and the lowest one in the western side. The analysis of the recent observations of W49B indicates that the remnant may be the result of an asymmetric bipolar explosion where the ejecta are collimated along a jet-like structure and the eastern jet is hotter and more Fe-rich than the western one. Another possible scenario associates the X-ray emission with a spherical explosion where parts of the ejecta are interacting with a dense belt of ambient material. To overcome this ambiguity we present new results of the analysis of an XMM-Newton observation and we perform estimates of the mass and energy of the remnant. We conclude that the scenario of an anisotropic jet-like explosion explains quite naturally our observation results, but the association of W49B with a hypernova and a gamma-ray burst, although still possible, is not directly supported by any evidence., Comment: 7 pages, 5 figures, accepted for publication in Advances in Space Research

In this contribution we discuss the 44Ti nucleosynthesis gamma-ray lines and their visibility with SIMBOL-X from simulations based on its expected sensitivity and spectro-imaging capabilities. The 44Ti radioactive nucleus can provide invaluable information on the details of supernova explosions. Its lifetime of about 85 yrs makes it the best indicator of the youth of these stellar explosions through its three gamma-ray lines at 67.9, 78.4 keV and 1.157 MeV. We focus on the youngest Galactic supernova remnants, namely: Cassiopeia A, for which the location and Doppler-velocity estimates of the 44Ti-emitting regions in the remnant would offer for the first time a unique view of nucleosynthesis processes which occurred in the innermost layers of the supernova; SN 1987A, in the Large Magellanic Cloud, whose progenitor is known, and for which the expected measurement of these lines would greatly constrain the stellar evolution models; Tycho and Kepler SNRs for which 44Ti lines have never been detected so far. The issue of the "young, missing and hidden" supernova remnants in the Galaxy will also be addressed using SIMBOL-X observations at the position of the 44Ti excesses that wide-field instruments like those onboard INTEGRAL and SWIFT/BAT should be able to reveal., Comment: 9 pages, 4 figures, invited talk submitted to the proceedings of "SIMBOL-X: the hard X-ray Universe in focus" conference, held May 14-16, 2007, Bologna, Italy (comments are welcome)

The density of the ambient medium where the supernova remnant evolves is a relevant parameter for its hydrodynamical evolution, for the mechanism of particle acceleration, and for the emission at TeV energies. Using XMM-Newton X-ray observations, we present a study of the ambient medium density of the historical supernova remnant SN 1006. We modelled the post-shock thermal emission to constrain the ambient medium density. Our study is focused on the North-West and the South-East rims of the remnant, where the thermal emission dominates. We used a plane-parallel shock plasma model plus another component for the ejecta that are not negligible in the regions of our study. The importance of the synchrotron component is also studied. In order to improve statistics, we combined several observations of the remnant. The density found in the South-East rim is low, roughly 0.05 cm-3, and seems to be representative of the rest of the remnant. However, in the North-West rim (close to the bright optical filament), the density is significantly higher (about 0.15-0.25 cm-3). This confirms a picture of SN 1006 evolving in a tenuous ambient medium, except in the North-West where the remnant has recently encountered a denser region. A density this low is compatible with the non-detection of the remnant by the HESS gamma-ray observatory. The lower density in the South-East implies a higher shock speed of 4900 km/s, higher than that of 2890 km/s measured in the North-West. This new estimate of the velocity could increase the maximum energy that accelerated particles can reach to energies of about 1 PeV., Comment: 8 pages, 4 figures, accepted for publication in A&A, Figure 3 corrected

We report the detection of both the 67.9 and 78.4 keV 44Sc gamma-ray lines in Cassiopeia A with the INTEGRAL IBIS/ISGRI instrument. Besides the robustness provided by spectro-imaging observations, the main improvements compared to previous measurements are a clear separation of the two 44Sc lines together with an improved significance of the detection of the hard X-ray continuum up to 100 keV. These allow us to refine the determination of the 44Ti yield and to constrain the nature of the nonthermal continuum emission. By combining COMPTEL, BeppoSAX/PDS and ISGRI measurements, we find a line flux of (2.5 +/- 0.3)*10(-5) cm(-2) s(-1) leading to a synthesized 44Ti mass of 1.6 (+0.6-0.3)*10(-4) solar mass. This high value suggests that Cas A is peculiar in comparison to other young supernova remnants, from which so far no line emission from 44Ti decay has been unambiguously detected., Comment: 5 pages, 4 figures, Accepted for publication in ApJL

In the framework of the study of supernova remnants and their complex interaction with the interstellar medium, we report on an XMM-Newton EPIC observation of the Galactic supernova remnant W49B. We investigate the spatial distribution of the chemical and physical properties of the plasma, so as to get important constraints on the physical scenario, on the dynamics of the supernova explosion, and on the interaction of the supernova remnant with the ambient interstellar clouds. We present line images, equivalent width maps, and a spatially resolved spectral analysis of a set of homogeneous regions. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca and Fe. In all the regions studied, the X-ray spectrum is dominated by the emission from the ejecta and there is no indication of radial stratification of the elements. A high overabundance of Ni (Ni/Ni_sun=10^{+2}_{-1}) is required in the bright central region and the previous detection of Cr and Mn line emission is confirmed. Spectra are well described by two thermal components in collisional ionization equilibrium. We observe spatial variations in the temperature, with the highest temperature found in the east and the lowest in the west. Our results support a scenario in which the X-ray emission comes from ejecta interacting with a dense belt of ambient material, but another possibility is that the remnant is the result of an asymmetric bipolar explosion with the eastern jet being hotter and more Fe-rich than the western jet. The eastern jet is confined by interaction with ambient molecular clouds. Comparison of the observed abundances with yields for hypernova and supernova nucleosynthesis does not directly support the association of W49B with a gamma-ray burst, although it remains possible., Comment: To be published in A&A. For the complete version of the paper, with all the figures included, please see http://www.astropa.unipa.it/Library/preprint.html

We present preliminary results of INTEGRAL/IBIS observations on Cas A, Tycho and Vela Junior Supernova remnants in the line emission of 44Ti. This radioactive nucleus is thought to be exclusively produced in supernovae during the first stages of the explosion. It has a lifetime of about 87 y and is then the best indicator of young SNRs, as exemplified by the detection of 44Ti in the youngest known Galactic SNR Cas A with GRO/COMPTEL and latter with BeppoSAX. In this paper, we will focus on this SNR for which we confirm the detection of 44Ti and point out the importance to know the nature of the hard X-ray continuum, the Tycho SNR, for which no indication of 44Ti was ever reported, and Vela Junior, for which the claimed detection of 44Ti with COMPTEL is still controversial. The INTEGRAL/IBIS observations bring new constraints on the nature of these SNRs and on the nucleosynthesis which took place during the explosions., Comment: Accepted for publication in New Astronomy Reviews ("Astronomy with Radioactivites V" conference, Clemson Univ., Sept. 2005). 6 pages, 2 figures

In the framework of test-particle and cosmic-ray modified hydrodynamics, we calculate synchrotron emission radial profiles in young ejecta-dominated supernova remnants (SNRs) evolving in an ambient medium which is uniform in density and magnetic field. We find that, even without any magnetic field amplification by Raleigh-Taylor instabilities, the radio synchrotron emission peaks at the contact discontinuity because the magnetic field is compressed and is larger there than at the forward shock. The X-ray synchrotron emission sharply drops behind the forward shock as the highest energy electrons suffer severe radiative losses., Comment: 8 pages, 6 figures, Accepted for publication in A&A