487 research outputs found
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
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
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
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
High School Science Teachers’ Perceptions of the Effects of One-To-One Computing Devices on Student Engagement
The identified problem of practice for the present action research study centers on ways in which teacher-participants in a working class poor, rural, southern high school can use the iPads in daily science classroom activities to more effectively to engage these students in their classrooms and make the curriculum meaningful. Data in the form of classroom observations, semi-structured interviews, and teacher in-service seminars was collected over a six week period. The results of the present action research study indicate a need for more professional development for incorporating iPads into science coursework for these teacher-participants at RHS despite their claim that they are well prepared to use the iPads in their science curriculum and pedagogy. The Action Plan that resulted from the present study is in the form of professional development for teachers that focuses on how iPads can be used in a constructivist pedagogy to enable better equity of historically marginalized groups of students such as young women, people of color, rural people, and working class poor people to access higher level science courses and post-secondary careers. The Action Plan details tools for iPad use with project-based learning that lends itself to student discovery, the creation of products, and personal meaning-making
The X-ray nebula of the filled center supernova remnant 3C58 and its interaction with the environment
An \xmm observation of the plerionic supernova remnant 3C58 has allowed us to
study the X-ray nebula with unprecedented detail. A spatially resolved spectral
analysis with a resolution of 8\arcsec has yielded a precise determination of
the relation between the spectral index and the distance from the center. We do
not see any evidence for bright thermal emission from the central core. In
contrast with previous ASCA and {\em Einstein} results, we derive an upper
limit to the black-body 0.5-10 keV luminosity and emitting area of \ergsec and cm, respectively, ruling out
emission from the hot surface of the putative neutron star and also excluding
the "outer-gap" model for hot polar caps. We have performed for the first time
a spectral analysis of the outer regions of the X-ray nebula, where most of the
emission is still non-thermal, but where the addition of a soft (kT=0.2-0.3
keV) optically thin plasma component is required to fit the spectrum at
keV. This component provides 6% of the whole remnant observed flux in the
0.5-10.0 keV band. We show that a Sedov interpretation is incompatible with the
SN1181-3C58 association, unless there is a strong deviation from electron-ion
energy equipartition, and that an origin of this thermal emission in terms of
the expansion of the nebula into the ejecta core nicely fits all the radio and
X-ray observations.Comment: 10 pages, 7 figures, accepted for publication in A&
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