16 research outputs found
X-Ray Emitting Ejecta of Supernova Remnant N132D
The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to
the rare class of oxygen-rich remnants, about a dozen objects that show optical
emission from pure heavy-element ejecta. They originate in explosions of
massive stars that produce large amounts of O, although only a tiny fraction of
that O is found to emit at optical wavelengths. We report the detection of
substantial amounts of O at X-ray wavelengths in a recent 100 ks Chandra ACIS
observation of N132D. A comparison between subarcsecond-resolution Chandra and
Hubble images reveals a good match between clumpy X-ray and optically emitting
ejecta on large (but not small) scales. Ejecta spectra are dominated by strong
lines of He- and H-like O; they exhibit substantial spatial variations
partially caused by patchy absorption within the LMC. Because optical ejecta
are concentrated in a 5 pc radius elliptical expanding shell, the detected
ejecta X-ray emission also originates in this shell.Comment: 5 pages, 6 figures, ApJ Letters, in pres
Dense, Fe-rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
We present observations of two LMC supernova remnants (SNRs), DEM L238 and
DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central
emission, surrounded by a faint shell, is present in both remnants. The central
emission has an entirely thermal spectrum dominated by strong Fe L-shell lines,
with the deduced Fe abundance in excess of solar and not consistent with the
LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and
DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission
originates in gas swept up and heated by the blast wave. A standard Sedov
analysis implies about 50 solar masses in both swept-up shells, SNR ages
between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and
subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich
supernova ejecta are close to collisional ionization equilibrium. Their
presence is unexpected, because standard Type Ia SNR models predict faint
ejecta emission with short ionization ages. Both SNRs belong to a previously
unrecognized class of Type Ia SNRs characterized by bright interior emission.
Denser than expected ejecta and/or a dense circumstellar medium around the
progenitors are required to explain the presence of Fe-rich ejecta in these
SNRs. Substantial amounts of circumstellar gas are more likely to be present in
explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar
SNRs could be remnants of ``prompt'' Type Ia explosions with young (~100 Myr
old) progenitors.Comment: 24 pages, 8 figures, ApJ, in pres
Dust Destruction in Type Ia Supernova Remnants in the Large Magellanic Cloud
We present first results from an extensive survey of Magellanic Clouds
supernova remnants (SNRs) with the Spitzer Space Telescope. We describe IRAC
and MIPS imaging observations at 3.6, 4.5, 5.8, 8, 24, and 70 microns of four
Balmer-dominated Type Ia SNRs in the Large Magellanic Cloud (LMC): DEM L71
(0505-67.9), 0509--67.5, 0519--69.0, and 0548-70.4. None was detected in the
four short-wavelength IRAC bands, but all four were clearly imaged at 24
microns, and two at 70 microns. A comparison of these images to Chandra
broadband X-ray images shows a clear association with the blast wave, and not
with internal X-ray emission associated with ejecta. Our observations are well
described by 1-D shock models of collisionally heated dust emission, including
grain size distributions appropriate for the LMC, grain heating by collisions
with both ions and electrons, and sputtering of small grains. Model parameters
are constrained by X-ray, optical, and far-ultraviolet observations. Our models
can reproduce observed 70/24 micron flux ratios only by including sputtering,
destroying most grains smaller than 0.03-0.04 microns in radius. We infer total
dust masses swept up by the SNR blast waves, before sputtering, of order 0.01
solar masses, several times less than those implied by a dust/gas mass ratio of
0.3 percent as often assumed for the LMC. Substantial dust destruction has
implications for gas-phase abundances.Comment: 11 pages, 1 figure, submitted to the Astrophysical Journal Letter
Ejecta, Dust, and Synchrotron Radiation in B0540-69.3: A More Crab-Like Remnant than the Crab
We present near and mid-infrared observations of the pulsar-wind nebula (PWN)
B0540-69.3 and its associated supernova remnant made with the {\it Spitzer
Space Telescope}. We report detections of the PWN with all four IRAC bands, the
24 m band of MIPS, and the Infrared Spectrograph (IRS). We find no
evidence of IR emission from the X-ray/radio shell surrounding the PWN
resulting from the forward shock of the supernova blast wave. The flux of the
PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths,
with a warm dust component longward of 20 m. We show that this dust
continuum can be explained by a small amount (\sim 1-3 \times 10^{-3} \msun)
of dust at a temperature of K, heated by the shock wave generated
by the PWN being driven into the inner edge of the ejecta. This is evidently
dust synthesized in the supernova. We also report the detection of several
lines in the spectrum of the PWN, and present kinematic information about the
PWN as determined from these lines. Kinematics are consistent with previous
optical studies of this object. Line strengths are also broadly consistent with
what one expects from optical line strengths. We find that lines arise from
slow ( km s) shocks driven into oxygen-rich clumps in the shell
swept-up by an iron-nickel bubble, which have a density contrast of relative to the bulk of the ejecta, and that faster shocks (
km s) in the hydrogen envelope are required to heat dust grains to
observed temperatures. We infer from estimates of heavy-element ejecta
abundances that the progenitor star was likely in the range of 20-25 .Comment: 46 pages, 10 figures, accepted for publication in Ap
Investigation of SARS-CoV-2 faecal shedding in the community: a prospective household cohort study (COVID-LIV) in the UK
Background
SARS-CoV-2 is frequently shed in the stool of patients hospitalised with COVID-19. The extent of faecal shedding of SARS-CoV-2 among individuals in the community, and its potential to contribute to spread of disease, is unknown.
Methods
In this prospective, observational cohort study among households in Liverpool, UK, participants underwent weekly nasal/throat swabbing to detect SARS-CoV-2 virus, over a 12-week period from enrolment starting July 2020. Participants that tested positive for SARS-CoV-2 were asked to provide a stool sample three and 14 days later. In addition, in October and November 2020, during a period of high community transmission, stool sampling was undertaken to determine the prevalence of SARS-CoV-2 faecal shedding among all study participants. SARS-CoV-2 RNA was detected using Real-Time PCR.
Results
A total of 434 participants from 176 households were enrolled. Eighteen participants (4.2%: 95% confidence interval [CI] 2.5–6.5%) tested positive for SARS-CoV-2 virus on nasal/throat swabs and of these, 3/17 (18%: 95% CI 4–43%) had SARS-CoV-2 detected in stool. Two of three participants demonstrated ongoing faecal shedding of SARS-CoV-2, without gastrointestinal symptoms, after testing negative for SARS-CoV-2 in respiratory samples. Among 165/434 participants without SARS-CoV-2 infection and who took part in the prevalence study, none had SARS-CoV-2 in stool. There was no demonstrable household transmission of SARS-CoV-2 among households containing a participant with faecal shedding.
Conclusions
Faecal shedding of SARS-CoV-2 occurred among community participants with confirmed SARS-CoV-2 infection. However, during a period of high community transmission, faecal shedding of SARS-CoV-2 was not detected among participants without SARS-CoV-2 infection. It is unlikely that the faecal-oral route plays a significant role in household and community transmission of SARS-CoV-2
The Expansion of the Young Supernova Remnant 0509-68.7 (N103B)
We present a second epoch of Chandra observations of the Type Ia Large Magellanic Cloud supernova remnant(SNR) 0509-68.7 (N103B) obtained in 2017. When combined with the earlier observations from 1999, we have a17.4 year baseline with which we can search for evidence of the remnant's expansion. Although the lack of strongpoint source detections makes absolute image alignment at the necessary accuracy impossible, we can measure thechange in the diameter and the area of the remnant, and find that it has expanded by an average velocity of 4170(2860, 5450) km s1. This supports the picture of this being a young remnant; this expansion velocity correspondsto an undecelerated age of 850 years, making the real age somewhat younger, consistent with results from lightecho studies. Previous infrared observations have revealed high densities in the western half of the remnant, likelyfrom circumstellar material, so it is probable that the real expansion velocity is lower on that side of the remnantand higher on the eastern side. A similar scenario is seen in Kepler's SNR. N103B joins the rare class ofMagellanic Cloud SNRs with measured proper motions