4,112 research outputs found
Asymmetries of Heavy Elements in the Young Supernova Remnant Cassiopeia A
Supernova remnants (SNRs) offer the means to study supernovae (SNe) long
after the original explosion and can provide a unique insight into the
mechanism that governs these energetic events. In this work, we examine the
morphologies of X-ray emission from different elements found in the youngest
known core-collapse (CC) SNR in the Milky Way, Cassiopeia A. The heaviest
elements exhibit the highest levels of asymmetry, which we relate to the
burning process that created the elements and their proximity to the center of
explosion. Our findings support recent model predictions that the material
closest to the source of explosion will reflect the asymmetries inherent to the
SN mechanism. Additionally, we find that the heaviest elements are moving more
directly opposed to the neutron star (NS) than the lighter elements. This
result is consistent with NS kicks arising from ejecta asymmetries.Comment: 12 pages, 4 figures, 2 tables Updated to include an analysis of
Emission Measure Maps (vs the, still-included, continuum-subtracted flux
maps), used as another proxy for mass maps. The results have not changed; the
emission measure maps also show increasing asymmetry with ejecta mass. (Now
matches the version published in ApJ. Vol 889 Issue 2 (2020) 144
The Age Evolution of the Radio Morphology of Supernova Remnants
Recent hydrodynamical models of supernova remnants (SNRs) demonstrate that
their evolution depends heavily on the inhomogeneities of the surrounding
medium. As SNRs expand, their morphologies are influenced by the non-uniform
and turbulent structure of their environments, as reflected in their radio
continuum emission. In this paper, we measure the asymmetries of 96 SNRs in
radio continuum images from three surveys of the Galactic plane and compare
these results to the SNRs' radii, which we use as a proxy for their age. We
find that larger (older) SNRs are more elliptical/elongated and more mirror
asymmetric than smaller (younger) SNRs, though the latter vary in their degrees
of asymmetry. This result suggests that SNR shells become more asymmetric as
they sweep up the interstellar medium (ISM), as predicted in hydrodynamical
models of SNRs expanding in a multi-phase or turbulent ISM.Comment: 16 pages, 5 figures, accepted by ApJ; sample expanded from 22 to 96
source
Evidence of Particle Acceleration in the Superbubble 30 Doradus C with NuSTAR
We present evidence of diffuse, non-thermal X-ray emission from the
superbubble 30 Doradus C (30 Dor C) using hard X-ray images and spectra from
NuSTAR observations. For this analysis, we utilize data from a 200 ks targeted
observation of 30 Dor C as well as 2.8 Ms of serendipitous off-axis
observations from the monitoring of nearby SN 1987A. The complete shell of 30
Dor C is detected up to 20 keV, and the young supernova remnant MCSNR
J0536-6913 in the southeast of 30 Dor C is not detected above 8 keV.
Additionally, six point sources identified in previous Chandra and XMM-Newton
investigations have hard X-ray emission coincident with their locations. Joint
spectral fits to the NuSTAR and XMM-Newton spectra across the 30 Dor C shell
confirm the non-thermal nature of the diffuse emission. Given the best-fit
rolloff frequencies of the X-ray spectra, we find maximum electron energies of
70-110 TeV (assuming a B-field strength of 4G), suggesting 30 Dor C is
accelerating particles. Particles are either accelerated via diffusive shock
acceleration at locations where the shocks have not stalled behind the
H shell, or cosmic-rays are accelerated through repeated acceleration
of low-energy particles via turbulence and magnetohydrodynamic waves in the
bubble's interior.Comment: 14 pages, 8 figures, ApJ, in pres
A Chandra View Of Nonthermal Emission In The Northwestern Region Of Supernova Remnant RCW 86: Particle Acceleration And Magnetic Fields
The shocks of supernova remnants (SNRs) are believed to accelerate particles
to cosmic ray (CR) energies. The amplification of the magnetic field due to CRs
propagating in the shock region is expected to have an impact on both the
emission from the accelerated particle population, as well as the acceleration
process itself. Using a 95 ks observation with the Advanced CCD Imaging
Spectrometer (ACIS) onboard the Chandra X-ray Observatory, we map and
characterize the synchrotron emitting material in the northwestern region of
RCW 86. We model spectra from several different regions, filamentary and
diffuse alike, where emission appears dominated by synchrotron radiation. The
fine spatial resolution of Chandra allows us to obtain accurate emission
profiles across 3 different non-thermal rims in this region. The narrow width
(l = 10''-30'') of these filaments constrains the minimum magnetic field
strength at the post-shock region to be approximately 80 {\mu}G.Comment: 7 pages, 3 figures, submitted for publication at the Astrophysical
Journa
Neural ODEs as a discovery tool to characterize the structure of the hot galactic wind of M82
Dynamic astrophysical phenomena are predominantly described by differential
equations, yet our understanding of these systems is constrained by our
incomplete grasp of non-linear physics and scarcity of comprehensive datasets.
As such, advancing techniques in solving non-linear inverse problems becomes
pivotal to addressing numerous outstanding questions in the field. In
particular, modeling hot galactic winds is difficult because of unknown
structure for various physical terms, and the lack of \textit{any} kinematic
observational data. Additionally, the flow equations contain singularities that
lead to numerical instability, making parameter sweeps non-trivial. We leverage
differentiable programming, which enables neural networks to be embedded as
individual terms within the governing coupled ordinary differential equations
(ODEs), and show that this method can adeptly learn hidden physics. We robustly
discern the structure of a mass-loading function which captures the physical
effects of cloud destruction and entrainment into the hot superwind. Within a
supervised learning framework, we formulate our loss function anchored on the
astrophysical entropy (). Our results demonstrate the
efficacy of this approach, even in the absence of kinematic data . We then
apply these models to real Chandra X-Ray observations of starburst galaxy M82,
providing the first systematic description of mass-loading within the
superwind. This work further highlights neural ODEs as a useful discovery tool
with mechanistic interpretability in non-linear inverse problems. We make our
code public at this GitHub repository
(https://github.com/dustindnguyen/2023_NeurIPS_NeuralODEs_M82).Comment: 9 Pages, 2 Figures, Accepted at the NeurIPS 2023 workshop on Machine
Learning and the Physical Science
The Role of Stellar Feedback in the Dynamics of HII Regions
Stellar feedback is often cited as the biggest uncertainty in galaxy
formation models today. This uncertainty stems from a dearth of observational
constraints as well as the great dynamic range between the small scales (<1 pc)
where the feedback occurs and the large scales of galaxies (>1 kpc) that are
shaped by this feedback. To bridge this divide, in this paper we aim to assess
observationally the role of stellar feedback at the intermediate scales of HII
regions. In particular, we employ multiwavelength data to examine several
stellar feedback mechanisms in a sample of 32 HII regions in the Large and
Small Magellanic Clouds (LMC and SMC, respectively). Using optical, infrared,
radio, and X-ray images, we measure the pressures exerted on the shells from
the direct stellar radiation, the dust-processed radiation, the warm ionized
gas, and the hot X-ray emitting gas. We find that the warm ionized gas
dominates over the other terms in all of the sources, although two have
comparable dust-processed radiation pressures to their warm gas pressures. The
hot gas pressures are comparatively weak, while the direct radiation pressures
are 1-2 orders of magnitude below the other terms. We discuss the implications
of these results, particularly highlighting evidence for hot gas leakage from
the HII shells and regarding the momentum deposition from the dust-processed
radiation to the warm gas. Furthermore, we emphasize that similar observational
work should be done on very young HII regions to test whether direct radiation
pressure and hot gas can drive the dynamics at early times.Comment: 19 pages, 8 figures; accepted by Ap
Spatially-Resolved Study of Recombining Plasma in W49B Using XMM-Newton
W49B is the youngest SNR to date that exhibits recombining plasma. The two
prevailing theories of this overionization are rapid cooling via adiabatic
expansion or through thermal conduction with an adjacent cooler medium. To
constrain the origin of the recombining plasma in W49B, we perform a
spatially-resolved spectroscopic study of deep XMM-Newton data across 46
regions. We adopt a 3-component model (with one ISM and two ejecta components),
and we find that recombining plasma is present throughout the entire SNR, with
increasing overionization from east to west. The latter result is consistent
with previous studies, and we attribute the overionization in the west to
adiabatic expansion. However, our findings contrast these prior works as we
find evidence of overionization in the east as well. As the SNR is interacting
with molecular material there, we investigate the plausibility of thermal
conduction as the origin of the rapid cooling. We show that based on the
estimated timescales, it is possible that small-scale thermal conduction
through evaporation of clumpy, dense clouds with a scale of 0.1-1.0 pc can
explain the observed overionization in the east.Comment: 19 pages, 8 figures, 2 tables, submitted to Ap
- …