162 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
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&
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
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.Comment: Accepted for publication in Astronomische Nachrichten. Proceedings of
the XMM-Newton Science Workshop 201
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.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
XMM-Newton Observation of the Black Hole Microquasar GRS 1758-258
The XMM-Newton X-ray observatory pointed the galactic black hole candidate
and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program
devoted to the scan of the Galactic Center regions. Preliminary results from
EPIC MOS camera data are presented here. The data indicate that the source
underwent a state transition from its standard low-hard state to an
intermediate state. For the first time in this source the ultra-soft component
of the accretion disk, which black hole binaries display in intermediate or
high-soft states, was clearly detected and measured thanks to the high spectral
capabilities of XMM-Newton.Comment: To appear in the Proc. of the Gamma-Ray Astrophysics 2001 Symposium,
4-6 April 2001, Baltimore, Maryland, U.S.A.. American Institute of Physics
(AIP) series: 5 pages, 6 PS figures, latex, uses aipproc.cls aipproc.st
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
XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source
We present new results from the observations of the supernova remnant (SNR) RX J1713.7–3946 (also G347.3–0.5) performed in five distinct pointings with the EPIC instrument on board the satellite XMM-Newton. RX J1713.7–3946 is a shelltype
SNR dominated by synchrotron radiation in the X-rays. Its emission (emission measure and photon index) as well as the absorption along the line-of-sight has been characterized over the entire SNR. The X-ray mapping of the absorbing column density has revealed strong well-constrained variations (0.4 × 1022 cm−2 ≤ NH ≤ 1.1 × 1022 cm−2) and, particularly, a strong absorption in the southwest. Moreover, there are several clues indicating that the shock front of RX J1713.7–3946 is impacting the clouds responsible for the absorption as revealed for instance by the positive correlation between X-ray absorption and X-ray brightness along the western rims. The CO and H observations show that the inferred cumulative absorbing column densities are in excellent agreement with the X-ray findings in different parts of the remnant on condition that the SNR lies at a distance of 1.3 ± 0.4 kpc, probably in the Sagittarius galactic arm, instead of the commonly-accepted value of 6 kpc. An excess in the CO emission is found in the southwest suggesting that the absorption is due to molecular clouds. A search for OH masers in the southwestern region has been unsuccessful, possibly due to the low density of the clouds. The X-ray mapping of the photon index has also revealed strong variations (1.8 ≤ Γ ≤ 2.6). The spectrum is steep in the faint central regions and
flat at the presumed shock locations, particularly in the southeast. Nevertheless, the regions where the shock impacts molecular clouds have a steeper spectrum than those where the shock propagates into a low density medium. The search for the thermal emission in RX J1713.7–3946 has been unsuccessful leading to a number density upper limit of 2 × 10−2 cm−3 in the ambient medium. This low density corresponds to a reasonable kinetic energy of the explosion provided that the remnant is less than a few thousand years old. A scenario based on a modified ambient medium due to the effect of a progenitor stellar wind is proposed and leads to an estimate of RX J1713.7–3946’s progenitor mass between 12 and 16 M. The X-ray bright central point source 1WGA J1713.4–3949 detected at the center of SNR RX J1713.7–3946 shows spectral properties very similar to those of the Compact Central Objects found in SNRs and consistent in terms of absorption with that of the central diffuse X-ray emission arising from the SNR. It is highly probable that the point source 1WGA J1713.4–3949 is the compact relic of RX J1713.7–3946’s supernova progenitor.Fil: Cassam Chenaï, G.. Centre D; FranciaFil: Decourchelle, A.. Centre D; FranciaFil: Ballet, J.;. Centre D; FranciaFil: Sauvageot, J. L.. Centre D; FranciaFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; Argentin
The warm interstellar medium around the Cygnus Loop
Observations of the oxygen lines [OII]3729 and [OIII]5007 in the medium
immediately beyond the Cygnus Loop supernova remnant were carried out with the
scanning Fabry-P\'erot spectrophotometer ESOP. Both lines were detected in
three different directions - east, northeast and southwest - and up to a
distance of 15 pc from the shock front. The ionized medium is in the immediate
vicinity of the remnant, as evinced by the smooth brightening of both lines as
the adiabatic shock transition (defined by the X-ray perimeter) is crossed.
These lines are usually brighter around the Cygnus Loop than in the general
background in directions where the galactic latitude is above 5 degrees. There
is also marginal (but significant) evidence that the degree of ionization is
somewhat larger around the Cygnus Loop. We conclude that the energy necessary
to ionize this large bubble of gas could have been supplied by an O8 or O9 type
progenitor or the particles heated by the expanding shock front. The second
possibility, though highly atractive, would have to be assessed by extensive
modelling.Comment: 18 pages, 8 figures, ApJ 512 in pres
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