491 research outputs found
XMM-Newton observations of the supernova remnant IC443: I. soft X-ray emission from shocked interstellar medium
The shocked interstellar medium around IC443 produces strong X-ray emission
in the soft energy band (E<1.5 keV). We present an analysis of such emission as
observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with
the purpose to find clear signatures of the interactions with the interstellar
medium (ISM) in the X-ray band, which may complement results obtained in other
wavelenghts. We found that the giant molecular cloud mapped in CO emission is
located in the foreground and gives an evident signature in the absorption of
X-rays. This cloud may have a torus shape and the part of torus interacting
with the IC443 shock gives rise to 2MASS-K emission in the southeast. The
measured density of emitting X-ray shocked plasma increases toward the
northeastern limb, where the remnant is interacting with an atomic cloud. We
found an excellent correlation between emission in the 0.3-0.5 keV band and
bright optical/radio filament on large spatial scales. The partial shell
structure seen in this band therefore traces the encounter with the atomic
cloud.Comment: 10 pages, 10 figures, accepted for publication in ApJ (20 September
2006, v649). For hi-res figures, see
http://www.astropa.unipa.it/Library/OAPA_preprints/ic443ele1.ps.g
XMM-Newton and Suzaku detection of an X-ray emitting shell around the pulsar wind nebula G54.1+0.3
Recent X-ray observations have proved to be very effective in detecting
previously unknown supernova remnant shells around pulsar wind nebulae (PWNe),
and in these cases the characteristics of the shell provide further clues on
the evolutionary stage of the embedded PWN. However, it is not clear why some
PWNe are still "naked". We carried out an X-ray observational campaign targeted
at the PWN G54.1+0.3, the "close cousin" of the Crab, with the aim to detect
the associated SNR shell. We analyzed an XMM-Newton and Suzaku observations of
G54.1+0.3 and we model out the contribution of dust scattering halo. We
detected an intrinsic faint diffuse X-ray emission surrounding a hard spectrum,
which can be modeled either with a power-law (gamma= 2.9) or with a thermal
plasma model (kT=2.0 keV.). If the shell is thermal, we derive an explosion
energy E=0.5-1.6x10^51 erg, a pre-shock ISM density of 0.2 cm^-3 and an age of
about 2000 yr. Using these results in the MHD model of PWN-SNR evolution, we
obtain an excellent agreement between the predicted and observed location of
the shell and PWN shock.Comment: Accepted for publication in A&A, 8 pages, 5 figures, full-res version
at http://www.astropa.inaf.it/Library/OAPA_preprints/h14298.pd
Linking gamma-ray spectra of supernova remnants to the cosmic ray injection properties in the aftermath of supernovae
The acceleration times of the highest-energy particles which emit gamma-rays
in young and middle-age SNRs are comparable with SNR age. If the number of
particles starting acceleration was varying during early times after the
supernova explosion then this variation should be reflected in the shape of the
gamma-ray spectrum. We use the solution of the non-stationary equation for
particle acceleration in order to analyze this effect. As a test case, we apply
our method to describe gamma-rays from IC443. As a proxy of the IC443 parent
supernova we consider SN1987A. First, we infer the time dependence of injection
efficiency from evolution of the radio spectral index in SN1987A. Then, we use
the inferred injection behavior to fit the gamma-ray spectrum of IC443. We show
that the break in the proton spectrum needed to explain the gamma-ray emission
is a natural consequence of the early variation of the cosmic ray injection,
and that the very-high energy gamma-rays originate from particles which began
acceleration during the first months after the supernova explosion. We conclude
that the shape of the gamma-ray spectrum observed today in SNRs critically
depends on the time variation of the cosmic ray injection process in the
immediate post explosion phases. With the same model, we estimate also the
possibility in the future to detect gamma-rays from SN 1987A.Comment: A&A, accepte
Hydrodynamic modelling of ejecta shrapnel in the Vela supernova remnant
Many supernova remnants (SNRs) are characterized by a knotty ejecta
structure. The Vela SNR is an excellent example of remnant in which detached
clumps of ejecta are visible as X-ray emitting bullets that have been observed
and studied in great detail. We aim at modelling the evolution of ejecta
shrapnel in the Vela SNR, investigating the role of their initial parameters
(position and density) and addressing the effects of thermal conduction and
radiative losses. We performed a set of 2-D hydrodynamic simulations describing
the evolution of a density inhomogeneity in the ejecta profile. We explored
different initial setups. We found that the final position of the shrapnel is
very sensitive to its initial position within the ejecta, while the dependence
on the initial density contrast is weaker. Our model also shows that moderately
overdense knots can reproduce the detached features observed in the Vela SNR.
Efficient thermal conduction produces detectable effects by determining an
efficient mixing of the ejecta knot with the surrounding medium and shaping a
characteristic elongated morphology in the clump.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Hard Extended X-ray Source in the IC 443 SNR Resolved by Chandra: A Fast Ejecta Fragment or a New Pulsar Wind Nebula?
A Chandra observation of the isolated hard X-ray source XMMU
J061804.3+222732, located in the region of apparent interaction of the
supernova remnant IC 443 with a molecular cloud, resolved the complex structure
of the source in a few bright clumps embedded in an extended emission of a ~ 30
arcsec size. The X-ray spectra of the clumps and the extended emission are
dominated by a hard power-law component with a photon index of 1.2--1.4. In
addition, we see some indications of an optically thin thermal plasma of a ~
0.3 keV temperature. The observed X-ray morphology and spectra are consistent
with those expected for an isolated supernova ejecta fragment interacting with
a dense ambient medium. A possible alternative interpretation is a pulsar wind
nebula associated with either IC 443 or another SNR, G189.6+3.3.Comment: Accepted for publication in The Astrophysical Journal Letters High
resolution Images of Fig.1 are appende
Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta
The remnants of core-collapse supernovae (SNe) have complex morphologies that
may reflect asymmetries and structures developed during the progenitor SN
explosion. Here we investigate how the morphology of the SNR Cassiopeia A (Cas
A) reflects the characteristics of the progenitor SN with the aim to derive the
energies and masses of the post-explosion anisotropies responsible for the
observed spatial distribution of Fe and Si/S. We model the evolution of Cas A
from the immediate aftermath of the progenitor SN to the three-dimensional
interaction of the remnant with the surrounding medium. The post-explosion
structure of the ejecta is described by small-scale clumping of material and
larger-scale anisotropies. The hydrodynamic multi-species simulations consider
an appropriate post-explosion isotopic composition of the ejecta. The observed
average expansion rate and shock velocities can be well reproduced by models
with ejecta mass and explosion energy erg. The post-explosion anisotropies (pistons)
reproduce the observed distributions of Fe and Si/S if they had a total mass of
and a total kinetic energy of erg. The pistons produce a spatial inversion of ejecta layers at the
epoch of Cas A, leading to the Si/S-rich ejecta physically interior to the
Fe-rich ejecta. The pistons are also responsible for the development of bright
rings of Si/S-rich material which form at the intersection between the reverse
shock and the material accumulated around the pistons during their propagation.
Our result supports the idea that the bulk of asymmetries observed in Cas A are
intrinsic to the explosion.Comment: 19 pages, 14 Figures; accepted for publication on Ap
Supernova 1987A: a Template to Link Supernovae to their Remnants
The emission of supernova remnants reflects the properties of both the
progenitor supernovae and the surrounding environment. The complex morphology
of the remnants, however, hampers the disentanglement of the two contributions.
Here we aim at identifying the imprint of SN 1987A on the X-ray emission of its
remnant and at constraining the structure of the environment surrounding the
supernova. We performed high-resolution hydrodynamic simulations describing SN
1987A soon after the core-collapse and the following three-dimensional
expansion of its remnant between days 1 and 15000 after the supernova. We
demonstrated that the physical model reproducing the main observables of SN
1987A during the first 250 days of evolution reproduces also the X-ray emission
of the subsequent expanding remnant, thus bridging the gap between supernovae
and supernova remnants. By comparing model results with observations, we
constrained the explosion energy in the range ~erg and
the envelope mass in the range . We found that the shape of
X-ray lightcurves and spectra at early epochs (<15 years) reflects the
structure of outer ejecta: our model reproduces the observations if the
outermost ejecta have a post-explosion radial profile of density approximated
by a power law with index . At later epochs, the shapes of X-ray
lightcurves and spectra reflect the density structure of the nebula around SN
1987A. This enabled us to ascertain the origin of the multi-thermal X-ray
emission, to disentangle the imprint of the supernova on the remnant emission
from the effects of the remnant interaction with the environment, and to
constrain the pre-supernova structure of the nebula.Comment: 16 pages, 11 Figures; accepted for publication on Ap
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