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[en] We present BeppoSAX spatially resolved observations of Cas A. The angular resolution of the MECS instrument allowed to spatially image some spectral characteristics and features of the SNR related with the temperature distribution in the source: fluxes in several energy bands, hardness ratio, and Fe line intensity have been mapped with arcmin angular resolution. Beside the astrophysical interest, these results give also information on the capability of BeppoSAX of observing extended sources
[en] Using a new long X-ray observation of the cluster of galaxies Sersic 159-03 with XMM-Newton, we derive radial temperature and abundance profiles using single- and multi-temperature models. The fits to the EPIC and RGS spectra prefer multi-temperature models especially in the core. The radial profiles of oxygen and iron measured with EPIC/RGS and the line profiles in RGS suggest that there is a dip in the O/Fe ratio in the centre of the cluster compared to its immediate surroundings. A possible explanation for the large scale metallicity distribution is that SNIa and SNII products are released in the ICMthrough ram-pressure stripping of in-falling galaxies. This causes a peaked metallicity distribution. In addition, SNIa in the central cD galaxy enrich mainly the centre of the cluster with iron. This excess of SNIa products is consistent with the low O/Fe ratio we detect in the centre of the cluster.We fit the abundances we obtain with yields from SNIa, SNII and Population-III stars to derive the clusters chemical evolution. We find that the measured abundance pattern does not require a Population-III star contribution. The relative contribution of the number of SNIa with respect to the total number of SNe which enrich the ICM is about 25-50%. Furthermore, we discuss the possible presence of a non-thermal component in the EPIC spectra. A potential source of this non-thermal emission can be inverse-Compton scattering between Cosmic Microwave Background (CMB) photons and relativistic electrons, which are accelerated in bow shocks associated with ram-pressure stripping of in-falling galaxies
[en] We study the 0509-67.5 supernova remnant in the Large Magellanic Cloud with the VLT/FORS2 spectrograph. We detect a broad component in the Hα emission with an FWHM of 2680 ± 70 km s-1 and 3900 ± 800 km s-1 for the southwest (SW) and northeast (NE) shocks, respectively. For the SW, the proton temperature appears to be too low for the shock velocity, which we attribute to a cosmic-ray pressure behind the shock front of at least 20% of the total pressure. For the NE, the post-shock proton temperature and the shock velocity are compatible, only if the plasma behind the shock front has a degree of thermal equilibrium of over 20%, which is at odds with current models for temperature equilibration behind fast shocks, which do not accelerate cosmic rays. If we assume the electron temperature to be less than 10% of the proton temperature, we find a post-shock cosmic-ray pressure of at least 7%.
[en] Many fast supernova remnant shocks show spectra dominated by Balmer lines. The Hα profiles have a narrow component explained by direct excitations and a thermally Doppler broadened component due to atoms that undergo charge exchange in the post-shock region. However, the standard model does not take into account the cosmic-ray shock precursor, which compresses and accelerates plasma ahead of the shock. In strong precursors with sufficiently high densities, the processes of charge exchange, excitation, and ionization will affect the widths of both narrow and broad line components. Moreover, the difference in velocity between the neutrals and the precursor plasma gives rise to frictional heating due to charge exchange and ionization in the precursor. In extreme cases, all neutrals can be ionized by the precursor. In this Letter we compute the ion and electron heating for a wide range of shock parameters, along with the velocity distribution of the neutrals that reach the shock. Our calculations predict very large narrow component widths for some shocks with efficient acceleration, along with changes in the broad-to-narrow intensity ratio used as a diagnostic for the electron-ion temperature ratio. Balmer lines may therefore provide a unique diagnostic of precursor properties. We show that heating by neutrals in the precursor can account for the observed Hα narrow component widths and that the acceleration efficiency is modest in most Balmer line shocks observed thus far.
[en] We study the electron-proton temperature equilibration behind several shocks of the RCW 86 supernova remnant. To measure the proton temperature, we use published and new optical spectra, all from different locations on the remnant. For each location, we determine the electron temperature from X-ray spectra, and correct for temperature equilibration between the shock front and the location of the X-ray spectrum. We confirm the result of previous studies that the electron and proton temperatures behind shock fronts are consistent with equilibration for slow shocks and deviate for faster shocks. However, we cannot confirm the previously reported trend of Te/Tp∝1/v2s.
[en] Several young supernova remnants (SNRs) have recently been detected in the high-energy (HE; 0.1 < E < 100 GeV) and very-high-energy (VHE; E > 100 GeV) gamma-ray domains. As exemplified by RX J1713.7-3946, the nature of this emission has been hotly debated, and direct evidence for the efficient acceleration of cosmic-ray protons at the SNR shocks still remains elusive. Here, we study the broadband gamma-ray emission from one of these young SNRs, namely RCW 86, for which several observational lines of evidence indirectly point towards the presence of accelerated hadrons. We then attempt to detect any putative hadronic signal from this SNR in the available gamma-ray data, in order to assess the level of acceleration efficiency. We also analyzed more than 40 months of data acquired by the Large Area Telescope (LAT) on-board the Fermi Gamma-Ray Space Telescope in the HE domain, and gathered all of the relevant multi-wavelength (from radio to VHE gamma-rays) information about the broadband nonthermal emission from RCW 86. For this purpose, we re-analyzed the archival X-ray data from the ASCA/Gas Imaging Spectrometer (GIS), the XMM-Newton/EPIC-MOS, and the RXTE/Proportional Counter Array (PCA). Beyond the expected Galactic diffuse background, no significant gamma-ray emission in the direction of RCW 86 is detected in any of the 0.1–1, 1–10 and 10–100 GeV Fermi-LAT maps. The derived HE upper limits, together with the H.E.S.S. measurements in the VHE domain, are incompatible with a standard D"−"2_p hadronic emission arising from proton-proton interactions, and can only be accommodated by a spectral index Γ ≤ 1.8, i.e. a value in-between the standard (test-particle) index and the asymptotic limit of theoretical particle spectra in the case of strongly modified shocks. In such a hadronic scenario, the total energy in accelerated particles is at the level of ηCR = ECR/ESN ~0.07 d"2_2_._5kpc/ñ (with the distance d_2_._5 _k_p_c ≡ d/2.5 kpc and the effective density ñ ≡ ñ /1 cm"-"3), and the average magnetic field must be stronger than 50 μG in order to significantly suppress any leptonic contribution. On the other hand, the interpretation of the gamma-ray emission by inverse Compton scattering of high energy electrons reproduces the multi-wavelength data using a reasonable value for the average magnetic field of 15–25 μG. In this leptonic scenario, we derive a conservative upper limit to ηCR of 0.04 d"2_2_._5 kpc/ñ. Furthermore, we discuss these results in the light of existing estimates of the magnetic field strength, the effective density and the acceleration efficiency in RCW 86.
[en] Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 Msun (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5+0.75-1.0 and 5.25+1.5-1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = -1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 x 104 Msun, similar to that of many of our Galaxy's most massive SFRs.
[en] This school, dedicated to young researchers, will clarify our present knowledge of the X-ray sky and give the opportunity to learn about the observatories and tools which are available. The contributions have been organized into 3 issues: -) fundamental physics, -) X-ray and Gamma-ray instruments and analysis techniques, and -) astrophysical objects. This document gathers only the slides of the presentations
[en] Supemovae and their remnants are the main Galactic nucleosynthesis sites and the privileged sources of Galactic cosmic rays. The youngest of such remnants can be studied through two distinct observational features: 44Tiγ-ray lines and the hard X-ray nonthermal continuum emission. The former gives unique information on the nucleosynthesis conditions occuring during the first stages of the explosion, while the latter provides clues on acceleration processes at supernova remnant shocks. In this contribution, we present new INTEGRAL results on Tycho, the remnant of a historical supernova, and on G1.9+0.3, which has been recently unveiled as the youngest Galactic supernova remnant. Expectations with Simbol-X are also addressed.
[en] We report on the analysis of the Chandra-ACIS data of O, B, and WR stars in the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars, and 3 WR-stars are analyzed and for the brighter sources, the epoch dependence of the X-ray fluxes is investigated. The O-stars in Cyg OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: . This relation is in excellent agreement with the one previously derived for the Carina OB1 association. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between LX and Lbol. Out of the three WR stars in Cyg OB2, probably only WR 144 is itself responsible for the observed level of X-ray emission, at a very low . The X-ray emission of the other two WR-stars (WR 145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind–wind interaction zone.