arXiv subjects

A. Decourchelle

Publications and source records attributed to A. Decourchelle.

At least 19 recordsLinked to original sources

arXiv2024

Bayesian insights in Tycho supernova remnant : a detailed mapping of ejecta properties

While Tycho's supernova remnant is one of the most studied type Ia Galactic supernova remnants, a global view of the physical properties of its ejecta is lacking, to understand its mysteries. In particular, the spatial distribution of the Si-rich ejecta line-of-sight velocity presents a large-scale unexplained asymmetry, with the north dominantly blueshifted and the south redshifted. To investigate the origin of this line-of-sight velocity asymmetry in the ejecta, we carry out a detailed X-ray spatially-resolved spectral analysis of the entire shocked ejecta in Tycho's SNR to determine the physical properties of its various components. This study is based on the archival deep X-ray observations from the Chandra space telescope. The spatially-resolved spectral analysis in 211 regions over the entire SNR is based on a tesselation method applied to the line-of-sight velocity map. A Bayesian tool is used to conduct the fitting, using a nested sampling algorithm. It allows us to obtain a complete view of the statistical landscape. We provide maps of the physical parameters of the various components across the SNR ejecta. The Doppler shift map confirms spectrally the large-scale north-south asymmetry in the line-of-sight velocity. We reveal different spatial distributions of temperature and ionization time for IMEs and for iron-rich ejecta, but none of these maps shows structure associated to the large-scale north-south asymmetry in the line-of-sight velocity distribution. The abundance maps show spatial variations, depending on the element, perhaps due to an origin in different layers during the explosion. We compare these abundances with some nucleosynthesis models. In addition, we observe for the first time an emission line at 0.654 keV possibly related to oxygen. Its spatial distribution differs from the other elements, so that this line may arise in the ambient medium.

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arXiv2014

Parametric studies of cosmic ray acceleration in supernova remnants

We present a library of numerical models of cosmic-ray accelerating supernova remnants (SNRs) evolving through a homogeneous ambient medium. We analyse distributions of the different energy components and diffusive shock acceleration time-scales for the models in various conditions. The library comprises a variety of SNR evolutionary scenarios and is used to map remnants with sufficiently known properties. This mapping constrains the respective ambient medium properties and the acceleration efficiency. Employing the library, we derive the ambient medium density, ambient magnetic field strength and the cosmic-ray acceleration efficiency for models of Tycho and SN 1006 remnants and refine the ages of SNR 0509-67.5 and SNR 0519-69.0.

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arXiv2014

Variation of the X-ray non-thermal emission in the Arches cloud

The origin of the iron fluorescent line at 6.4 keV from an extended region surrounding the Arches cluster is debated and the non-variability of this emission up to 2009 has favored the low-energy cosmic-ray origin over a possible irradiation by hard X-rays. By probing the variability of the Arches cloud non-thermal emission in the most recent years, including a deep observation in 2012, we intend to discriminate between the two competing scenarios. We perform a spectral fit of XMM-Newton observations collected from 2000 to 2013 in order to build the Arches cloud lightcurve corresponding to both the neutral Fe Kalpha line and the X-ray continuum emissions. We reveal a 30% flux drop in 2012, detected with more than 4 sigma significance for both components. This implies that a large fraction of the studied non-thermal emission is due to the reflection of an X-ray transient source.

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arXiv2014

Shock-cloud interaction and particle acceleration in SN 1006

The supernova remnant SN 1006 is a powerful source of high-energy particles and evolves in a relatively tenuous and uniform environment, though interacting with an atomic cloud in its northwestern limb. The X-ray image of SN 1006 reveals an indentation in the southwestern part of the shock front and the HI maps show an isolated cloud (southwestern cloud) having the same velocity as the northwestern cloud and whose morphology fits perfectly in the indentation. We performed spatially resolved spectral analysis of a set of small regions in the southwestern nonthermal limb and studied the deep X-ray spectra obtained within the XMM-Newton SN 1006 Large Program. We also analyzed archive HI data, obtained combining single dish and interferometric observations. We found that the best-fit value of the N_H derived from the X-ray spectra significantly increases in regions corresponding to the southwestern cloud, while the cutoff energy of the synchrotron emission decreases. The amount of the N_H variations corresponds perfectly with the HI column density of the southwestern cloud, as measured from the radio data. The decrease in the cutoff energy at the indentation clearly reveals that the back side of the cloud is actually interacting with the remnant. The southwestern limb therefore presents a unique combination of efficient particle acceleration and high ambient density, thus being the most promising region for gamma-ray hadronic emission in SN 1006. We estimate that such emission will be detectable with the Fermi telescope within a few years.

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arXiv2013

Athena+: The first Deep Universe X-ray Observatory

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.

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arXiv2013

The loss-limited electron energy in SN 1006: effects of the shock velocity and of the diffusion process

The spectral shape of the synchrotron X-ray emission from SN 1006 reveals the fundamental role played by radiative losses in shaping the high-energy tail of the electron spectrum. We analyze data from the XMM-Newton SN 1006 Large Program and confirm that in both nonthermal limbs the loss-limited model correctly describes the observed spectra. We study the physical origin of the observed variations of the synchrotron cutoff energy across the shell. We investigate the role played by the shock velocity and by the electron gyrofactor. We found that the cutoff energy of the syncrotron X-ray emission reaches its maximum value in regions where the shock has experienced its highest average speed. This result is consistent with the loss-limited framework. We also find that the electron acceleration in both nonthermal limbs of SN 1006 proceeds close to the Bohm diffusion limit, the gyrofactor being in the range 1.5-4. We finally investigate possible explanations for the low values of cutoff energy measured in thermal limbs.

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arXiv2013

The shape of the cutoff in the synchrotron emission of SN 1006 observed with XMM-Newton

Synchrotron X-ray emission from the rims of young supernova remnants allows us to study the high-energy tail of the electrons accelerated at the shock front. The analysis of X-ray spectra can provide information on the physical mechanisms that limit the energy achieved by the electrons in the acceleration process. We aim at verifying whether the maximum electron energy in SN 1006 is limited by synchrotron losses and at obtaining information on the shape of the cutoff in the X-ray synchrotron emission. We analyzed the deep observations of the XMM-Newton SN 1006 Large Program. We performed spatially resolved spectral analysis of a set of small regions in the nonthermal limbs and studied the X-ray spectra by adopting models that assume different electron spectra. We found out that a loss-limited model provides the best fit to all the spectra and this indicates that the shape of the cutoff in the electron momentum (p) distribution has the form exp[-(p/p_cut)^2]. We also detected residual thermal emission from shocked ambient medium and confirmed the reliability of previous estimates of the post-shock density. Our results indicate that radiative losses play a fundamental role in shaping the electron spectrum in SN 1006.

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arXiv2013

The Hot and Energetic Universe: The astrophysics of supernova remnants and the interstellar medium

The study of both supernova remnants and the hot and cold phases of the interstellar medium are essential for understanding the final stages of stellar evolution and their feedback on the evolution of galaxies through injection of energy and heavy elements. These studies are also crucial for understanding the physics of supernovae, their cosmological implication, and the origin of galactic cosmic rays. The unique capabilities of Athena+ will allow us to explore a new parameter space. Spatially-resolved high-resolution spectroscopy using Athena+ X-IFU of young remnants will allow to characterize individual parcels of ejected material in the line of sight in terms of kinematics, ionization and composition, providing access to the three dimensional geometry of the explosion. Athena+ will also allow studying shock physics and particle acceleration in supernova remnants, as well as their interaction with their environment. Athena+ X-IFU will also characterize the ionization mechanisms competing in forming the complex structures of the hot interstellar medium, likely to keep the echo of past star formation activity, both in our Galaxy and nearby ones. For the first time the dust and gas of the densest cold medium, like in the Galactic Centre environment, will be studied. Athena+ X-IFU will observe, along with the Mg K and Si K edges, which are the main tracers of the silicates content of the ISM, the Fe K edge with unprecedented sensitivity and energy-resolution. This will allow us to study for the first time the nature of Fe-bearing dust in such regions.

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arXiv2012

XMM-Newton evidence of shocked ISM in SN 1006: indications of hadronic acceleration

Shock fronts in young supernova remnants are the best candidates for being sites of cosmic ray acceleration up to a few PeV, though conclusive experimental evidence is still lacking. Hadron acceleration is expected to increase the shock compression ratio, providing higher postshock densities, but X-ray emission from shocked ambient medium has not firmly been detected yet in remnants where particle acceleration is at work. We exploited the deep observations of the XMM-Newton Large Program on SN 1006 to verify this prediction. We performed spatially resolved spectral analysis of a set of regions covering the southeastern rim of SN 1006. We studied the spatial distribution of the thermodynamic properties of the ambient medium and carefully verified the robustness of the result with respect to the analysis method. We detected the contribution of the shocked ambient medium. We also found that the postshock density of the interstellar medium significantly increases in regions where particle acceleration is efficient. Under the assumption of uniform preshock density, we found that the shock compression ratio reaches a value of ~6 in regions near the nonthermal limbs. Our results support the predictions of shock modification theory and indicate that effects of acceleration of cosmic ray hadrons on the postshock plasma can be observed in supernova remnants.

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arXiv2012

Athena (Advanced Telescope for High ENergy Astrophysics) Assessment Study Report for ESA Cosmic Vision 2015-2025

Athena is an X-ray observatory-class mission concept, developed from April to December 2011 as a result of the reformulation exercise for L-class mission proposals in the framework of ESA's Cosmic Vision 2015-2025. Athena's science case is that of the Universe of extremes, from Black Holes to Large-scale structure. The specific science goals are structured around three main pillars: "Black Holes and accretion physics", "Cosmic feedback" and "Large-scale structure of the Universe". Underpinning these pillars, the study of hot astrophysical plasmas offered by Athena broadens its scope to virtually all corners of Astronomy. The Athena concept consists of two co-aligned X-ray telescopes, with focal length 12 m, angular resolution of 10" or better, and totalling an effective area of 1 m2 at 1 keV (0.5 m2 at 6 keV). At the focus of one of the telescopes there is a Wide Field Imager (WFI) providing a field of view of 24'\times 24', 150 eV spectral resolution at 6 keV, and high count rate capability. At the focus of the other telescope there is the X-ray Microcalorimeter Spectrometer (XMS), a cryogenic instrument offering a spectral resolution of 3 eV over a field of view of 2.3' \times 2.3'. Although Athena has not been selected as ESA's Cosmic Vision 2015-2025 L1 mission, its science goals and concept conform the basis of what should become ESA's X-ray astronomy flagship.

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arXiv2011

The COSPIX mission: focusing on the energetic and obscured Universe

Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions, are recognized as key science objectives to be addressed by the next generation of instruments. These are the main goals of the COSPIX proposal, made to ESA in December 2010 in the context of its call for selection of the M3 mission. In addition, COSPIX, will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusters of galaxies. COSPIX is proposed as an observatory operating from 0.3 to more than 100 keV. The payload features a single long focal length focusing telescope offering an effective area close to ten times larger than any scheduled focusing mission at 30 keV, an angular resolution better than 20 arcseconds in hard X-rays, and polarimetric capabilities within the same focal plane instrumentation. In this paper, we describe the science objectives of the mission, its baseline design, and its performances, as proposed to ESA.

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arXiv2010

Fading hard X-ray emission from the Galactic Centre molecular cloud Sgr B2

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.

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arXiv2010

Spatial identification of the overionized plasma in W49B

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

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arXiv2009

A joint spectro-imaging analysis of the XMM-Newton and HESS observations of the supernova remnant RX J1713.7-3946

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.

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arXiv2008

Science with Simbol-X

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.

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arXiv2007

The gas density around SN 1006

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.

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arXiv2007

44Ti nucleosynthesis gamma-ray lines with SIMBOL-X

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.

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arXiv2007

A physical interpretation of the jet-like X-ray emission from supernova remnant W49B

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.

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