245 research outputs found
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.Comment: 13 pages, 9 figures, MNRAS accepte
3D Simulations of the Thermal X-ray Emission from Young Supernova Remnants Including Efficient Particle Acceleration
Supernova remnants (SNRs) are believed to be the major contributors to
Galactic cosmic rays. The detection of non-thermal emission from SNRs
demonstrates the presence of energetic particles, but direct signatures of
protons and other ions remain elusive. If these particles receive a sizeable
fraction of the explosion energy, the morphological and spectral evolution of
the SNR must be modified. To assess this, we run 3D hydrodynamic simulations of
a remnant coupled with a non-linear acceleration model. We obtain the
time-dependent evolution of the shocked structure, impacted by the
Rayleigh-Taylor hydrodynamic instabilities at the contact discontinuity and by
the back-reaction of particles at the forward shock. We then compute the
progressive temperature equilibration and non-equilibrium ionization state of
the plasma, and its thermal emission in each cell. This allows us to produce
the first realistic synthetic maps of the projected X-ray emission from the
SNR. Plasma conditions (temperature, ionization age) can vary widely over the
projected surface of the SNR, especially between the ejecta and the ambient
medium owing to their different composition. This demonstrates the need for
spatially-resolved spectroscopy. We find that the integrated emission is
reduced with particle back-reaction, with the effect being more significant for
the highest photon energies. Therefore different energy bands, corresponding to
different emitting elements, probe different levels of the impact of particle
acceleration. Our work provides a framework for the interpretation of SNR
observations with current X-ray missions (Chandra, XMM-Newton, Suzaku) and with
upcoming X-ray missions (such as Astro-H).Comment: Accepted for publication in ApJ. Figures quality has been reduced for
the arXi
XMM-Newton observation of Kepler's supernova remnant
We present the first results coming from the observation of Kepler's
supernova remnant obtained with the EPIC instruments on board the XMM-Newton
satellite. We focus on the images and radial profiles of the emission lines (Si
K, Fe L, Fe K) and of the high energy continuum. Chiefly, the Fe L and Si K
emission-line images are generally consistent with each other and the radial
profiles show that the Si K emission extends to a larger radius than the Fe L
emission (distinctly in the southern part of the remnant). Therefore, in
contrast to Cas A, no inversion of the Si- and Fe-rich ejecta layers is
observed in Kepler. Moreover, the Fe K emission peaks at a smaller radius than
the Fe L emission, which implies that the temperature increases inwards in the
ejecta. The 4-6 keV high energy continuum map shows the same distribution as
the asymmetric emission-line images except in the southeast where there is a
strong additional emission. A two color image of the 4-6 keV and 8-10 keV high
energy continuum illustrates that the hardness variations of the continuum are
weak all along the remnant except in a few knots. The asymmetry in the Fe K
emission-line is not associated with any asymmetry in the Fe K equivalent width
map. The Si K maps lead to the same conclusions. Hence, abundance variations do
not cause the north-south brightness asymmetry. The strong emission in the
north may be due to overdensities in the circumstellar medium. In the
southeastern region of the remnant, the lines have a very low equivalent width
and the X-ray emission is largely nonthermal.Comment: 15 pages, 15 figures, accepted for publication in A&
XMM-Newton Large Program on SN1006 - II: Thermal Emission
Based on the XMM-Newton large program on SN1006 and our newly developed
spatially resolved spectroscopy tools (Paper~I), we study the thermal emission
from ISM and ejecta of SN1006 by analyzing the spectra extracted from 583
tessellated regions dominated by thermal emission. With some key improvements
in spectral analysis as compared to Paper~I, we obtain much better spectral
fitting results with less residuals. The spatial distributions of the thermal
and ionization states of the ISM and ejecta show different features, which are
consistent with a scenario that the ISM (ejecta) is heated and ionized by the
forward (reverse) shock propagating outward (inward). Different elements have
different spatial distributions and origins, with Ne mostly from the ISM, Si
and S from the ejecta, and O and Mg from both ISM and ejecta. Fe L-shell lines
are only detected in a small shell-like region SE to the center of SN1006,
indicating that most of the Fe-rich ejecta has not yet or just recently been
reached by the reverse shock. The overall ejecta abundance patterns for most of
the heavy elements, except for Fe and sometimes S, are consistent with typical
Type~Ia SN products. The NW half of the SNR interior probably represents a
region with turbulently mixed ISM and ejecta, so has enhanced emission from O,
Mg, Si, S, lower ejecta temperature, and a large diversity of ionization age.
In addition to the asymmetric ISM distribution, an asymmetric explosion of the
progenitor star is also needed to explain the asymmetric ejecta distribution.Comment: 9 pages, 7 figures, 1 table, MNRAS in pres
XMM-Newton Large Program on SN1006 - I: Methods and Initial Results of Spatially-Resolved Spectroscopy
Based on our newly developed methods and the XMM-Newton large program of
SN1006, we extract and analyze the spectra from 3596 tessellated regions of
this SNR each with 0.3-8 keV counts . For the first time, we map out
multiple physical parameters, such as the temperature (), electron density
(), ionization parameter (), ionization age (), metal
abundances, as well as the radio-to-X-ray slope () and cutoff frequency
() of the synchrotron emission. We construct probability
distribution functions of and , and model them with several
Gaussians, in order to characterize the average thermal and ionization states
of such an extended source. We construct equivalent width (EW) maps based on
continuum interpolation with the spectral model of each regions. We then
compare the EW maps of OVII, OVIII, OVII K, Ne, Mg, SiXIII,
SiXIV, and S lines constructed with this method to those constructed with
linear interpolation. We further extract spectra from larger regions to confirm
the features revealed by parameter and EW maps, which are often not directly
detectable on X-ray intensity images. For example, O abundance is consistent
with solar across the SNR, except for a low-abundance hole in the center. This
"O Hole" has enhanced OVII K and Fe emissions, indicating
recently reverse shocked ejecta, but also has the highest , indicating
forward shocked ISM. Therefore, a multi-temperature model is needed to
decompose these components. The asymmetric metal distributions suggest there is
either an asymmetric explosion of the SN or an asymmetric distribution of the
ISM.Comment: 25 pages, 18 figures, 4 tables, MNRAS, in pres
The X-ray flaring activity of the galactic nucleus observed with XMM-Newton
We report the results of XMM-Newton observations of Sgr A*, the radiative
counterpart of the massive black hole at the nucleus of our Galaxy, performed
in the frame of the guaranteed time survey program of the Galactic Center
region. The discovery of bright X-ray flares from Sgr A* with Chandra in
October 2000 have opened new perspectives to understand the processes at work
in this object and in general in black holes accreting at low accretion rates.
We report here the important results obtained with XMM-Newton on the Sgr A*
high-energy flaring activity and we discuss the implications on the models and
the future observational perspectives.Comment: 4 pages, 3 figures, proc. of the SF2A conf. held in Bordeaux, France,
June 2003, eds.: F. Combes, D. Barret and T. Contini, EdP-Sciences Conf.
Serie
Hydrodynamic Simulation of Supernova Remnants Including Efficient Particle Acceleration
A number of supernova remnants (SNRs) show nonthermal X-rays assumed to be
synchrotron emission from shock accelerated TeV electrons. The existence of
these TeV electrons strongly suggests that the shocks in SNRs are sources of
galactic cosmic rays (CRs). In addition, there is convincing evidence from
broad-band studies of individual SNRs and elsewhere that the particle
acceleration process in SNRs can be efficient and nonlinear. If SNR shocks are
efficient particle accelerators, the production of CRs impacts the thermal
properties of the shock heated, X-ray emitting gas and the SNR evolution. We
report on a technique that couples nonlinear diffusive shock acceleration,
including the backreaction of the accelerated particles on the structure of the
forward and reverse shocks, with a hydrodynamic simulation of SNR evolution.
Compared to models which ignore CRs, the most important hydrodynamical effects
of placing a significant fraction of shock energy into CRs are larger shock
compression ratios and lower temperatures in the shocked gas. We compare our
results, which use an approximate description of the acceleration process, with
a more complete model where the full CR transport equations are solved (i.e.,
Berezhko et al., 2002), and find excellent agreement for the CR spectrum summed
over the SNR lifetime and the evolving shock compression ratio. The importance
of the coupling between particle acceleration and SNR dynamics for the
interpretation of broad-band continuum and thermal X-ray observations is
discussed.Comment: Accepted for publication in A & A; 14 pages including 11 figure
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