38 research outputs found
Electron-Ion Temperature Equilibration at Collisionless Shocks in Supernova Remnants
The topic of this review is the current state of our knowledge about the
degree of initial equilibration between electrons, protons and ions at
supernova remnant (SNR) shocks. Specifically, the question has been raised as
to whether there is an inverse relationship between the shock velocity and the
equilibration similar to the relationship between equilibration and Alfven Mach
number seen in interplanetary shocks (Schwartz et al 1988). This review aims to
compile every method that has been used to measure the equilibration and every
SNR on which they have been tested. I review each method, its problems and
uncertainties and how those would effect the degree of equilibration (or
velocity) inferred. The final compilation of observed electron to proton
temperature ratios as a function of shock velocity gives an accurate,
conservative picture of the state of our knowledge and the avenues we need to
pursue to make progress in our understanding of the relation between the
velocity of a shock and the degree of equilibration.Comment: Invited talk, accepted for publication in Advances in Space Research;
proceedings of session E1.4 of the 35th COSPAR Scientific Assembly, Paris,
July 18-25 2004, 'Young Neutron Stars and Supernova Remnants', edited by C.
Rakowski and S. Chatterjee, 16 preprint pages including 6 figure
Supernova Remnant Kes 17: Efficient Cosmic Ray Accelerator inside a Molecular Cloud
Supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number
of remnants detected across the electromagnetic spectrum. In this paper, we
analyze recent radio, X-ray, and gamma-ray observations of this object,
determining that efficient cosmic ray acceleration is required to explain its
broadband non-thermal spectrum. These observations also suggest that Kes 17 is
expanding inside a molecular cloud, though our determination of its age depends
on whether thermal conduction or clump evaporation is primarily responsible for
its center-filled thermal X-ray morphology. Evidence for efficient cosmic ray
acceleration in Kes 17 supports recent theoretical work that the strong
magnetic field, turbulence, and clumpy nature of molecular clouds enhances
cosmic ray production in supernova remnants. While additional observations are
needed to confirm this interpretation, further study of Kes 17 is important for
understanding how cosmic rays are accelerated in supernova remnants.Comment: 13 pages, 6 figures, 4 table
Ion Charge States in Halo CMEs: What can we Learn about the Explosion?
We describe a new modeling approach to develop a more quantitative
understanding of the charge state distributions of the ions of various elements
detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced
Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution
based on observations of CMEs propagating in the plane of the sky and on
theoretical models, we integrate time dependent equations for the ionization
balance of various elements to compare with ACE data. We find that plasma in
the CME ``core'' typically requires further heating following filament
eruption, with thermal energy input similar to the kinetic energy input. This
extra heating is presumably the result of post eruptive reconnection. Plasma
corresponding to the CME ``cavity'' is usually not further ionized, since
whether heated or not, the low density gives freeze-in close the the Sun. The
current analysis is limited by ambiguities in the underlying model CME
evolution. Such methods are likely to reach their full potential when applied
to data to be acquired by STEREO when at optimum separation. CME evolution
observed with one spacecraft may be used to interpret CME charge states
detected by the other.Comment: 20 pages, accepted by Ap
Electron Heating and Cosmic Rays at a Supernova Shock from Chandra X-ray Observations of E0102.2-7219
In this Letter we use the unprecedented spatial resolution of the Chandra
X-ray Observatory to carry out, for the first time, a measurement of the
post-shock electron temperature and proper motion of a young SNR, specifically
to address questions about the post-shock partition of energy among electrons,
ions, and cosmic rays. The expansion rate, 0.100 +/- 0.025 percent per yr, and
inferred age, ~1000 yr, of E0102.2-7219, from a comparison of X-ray
observations spanning 20 years, are fully consistent with previous estimates
based on studies of high velocity oxygen-rich optical filaments in the remnant.
With a radius of 6.4 pc for the blast wave estimated from the Chandra image,
our expansion rate implies a blast wave velocity of ~6000 km/s and a range of
electron temperatures 2.5 - 45 keV, dependent on the degree of collisionless
electron heating. Analysis of the Chandra ACIS spectrum of the immediate
post-shock region reveals a thermal plasma with abundances and column density
typical of the Small Magellanic Cloud and an electron temperature of 0.4-1 keV.
The measured electron temperature is significantly lower than the plausible
range above, which can only be reconciled if we assume that a significant
fraction of the shock energy, rather than contributing to the heating of the
post-shock electrons and ions, has gone into generating cosmic rays.Comment: 13 pages, including 2 postscript figs, LaTeX. Accepted by Ap
The Chandra View of the Supernova Remnant 0506-68.0 in the Large Magellanic Cloud
A new Chandra observation of SNR 0506-68.0 (also called N23) reveals a
complex, highly structured morphology in the low energy X-ray band and an
isolated compact central object in the high energy band. Spectral analysis
indicates that the X-ray emission overall is dominated by thermal gas whose
composition is consistent with swept-up ambient material. There is a strong
gradient in ambient density across the diameter of the remnant. Toward the
southeast, near a prominent star cluster, the emitting density is 10 - 23
cm^{-3} while toward the northwest it has dropped to a value of only 1 cm^{-3}.
The total extent of the X-ray remnant is 100" by 120" (24 pc x 29 pc for a
distance of 50 kpc), somewhat larger than previously known. The remnant's age
is estimated to be ~4600 yr. One part of the remnant shows evidence for
enhanced O, Ne, and perhaps Mg abundances, which is interpreted as evidence for
ejecta from a massive star core collapse supernova. The compact central object
has a luminosity of a few times 10^{33} ergs/s and no obvious radio or optical
counterpart. It does not show an extended nebula or pulsed emission as expected
from a young energetic pulsar, but resembles the compact central objects seen
in other core collapse SNe, such as Cas A.Comment: 5 pages, including 3 postscript figs, LaTeX, accepted to appear in
ApJ Letter
Iron-Rich Ejecta in the Supernova Remnant DEM L71
Chandra X-ray observations of DEM L71, a supernova remnant (SNR) in the Large
Magellanic Cloud (LMC), reveal a clear double shock morphology consisting of an
outer blast wave shock surrounding a central bright region of reverse-shock
heated ejecta. The abundances of the outer shock are consistent with LMC
values, while the ejecta region shows enhanced abundances of Si, Fe, and other
species. However, oxygen is not enhanced in the ejecta; the Fe/O abundance
ratio there is more than 5 times the solar ratio. Based on the relative
positions of the blast wave shock and the contact discontinuity in the context
of SNR evolutionary models, we determine a total ejecta mass of approximately
1.5 solar masses. Ejecta mass estimates based on emission measures derived from
spectral fits are subject to considerable uncertainty due to lack of knowledge
of the true contribution of hydrogen continuum emission. Maximal mass
estimates, i.e., assuming no hydrogen, result in 1.5 solar masses of Fe and
0.24 solar masses of Si. Under the assumption that an equal quantity of
hydrogen has been mixed into the ejecta, we estimate 0.8 solar masses of Fe and
0.12 solar masses of Si. These characteristics support the view that in DEM L71
we see Fe-rich ejecta from a Type Ia SN several thousand years after explosion.Comment: 5 pages, including 3 postscript figs, LaTeX, to appear in ApJ Letters
2003 Jan 1
The Physics of Supernova Remnant Blast Waves. I. Kinematics of DEM L71 in the Large Magellanic Cloud
We present the results from Fabry-Perot imaging spectroscopy of the
Balmer-dominated supernova remnant DEM L71 (0505-67.9) in the LMC. Spectra
extracted from the entire circumference of the blast wave reveal the broad and
narrow component H-alpha line emission characteristic of non-radiative shocks
in partially neutral gas. The new spectra of DEM L71 include portions of the
rim that have not been previously observed. We find that the broad component
width varies azimuthally along the edge of DEM L71, ranging from 450+/-60 km/s
along the eastern edge to values as high as 985 (+210)(-165) km/s along the
faint western edge. In part of the faint northern rim the broad component is
not detected, possibly indicating a lower density in these regions and/or a
broad component width in excess of 1000 km/s. Between the limits of zero and
full electron-ion temperature equilibration at the shock front, the allowed
range of shock velocities is 430-560 km/s along the east rim and 700-1250 km/s
along other parts of the blast wave. The H-alpha broad-to-narrow flux ratios
vary considerably around the remnant, ranging from 0.4 to 0.8. These ratios lie
below the values predicted by our shock models. We find that narrow component
H-alpha emission from a cosmic ray precursor may be the cause of the
discrepancy. The least decelerated portions of the blast wave (i.e., regions
excluding the brightest filaments) are well characterized by Sedov models with
a kinetic energy E_51= (0.37+/-0.06)*D_50**(5/2), where D_50 is the LMC
distance in units of 50 kpc. The corresponding age for DEM L71 is
(4360+/-290)*D_50 yr. This is the first time that velocity information from the
entire blast wave has been utilized to study the global kinematics of a
non-radiative SNR at a known distance.Comment: 21 pages, including 8 postscript figures and 4 tables, LaTeX,
accepted to ApJ; see companion pape