154 research outputs found
A Detailed Kinematic Map of Cassiopeia A's Optical Main Shell and Outer High-Velocity Ejecta
We present three-dimensional kinematic reconstructions of optically emitting
material in the young Galactic supernova remnant Cassiopeia A (Cas A). These
Doppler maps have the highest spectral and spatial resolutions of any previous
survey of Cas A and represent the most complete catalog of its optically
emitting material to date. We confirm that the bulk of Cas A's optically bright
ejecta populate a torus-like geometry tilted approximately 30 degrees with
respect to the plane of the sky with a -4000 to +6000 km/s radial velocity
asymmetry. Near-tangent viewing angle effects and an inhomogeneous surrounding
CSM/ISM environment suggest that this geometry and velocity asymmetry may not
be faithfully representative of the remnant's true 3D structure or the
kinematic properties of the original explosion. The majority of the optical
ejecta are arranged in several well-defined and nearly circular ring-like
structures with diameters between approximately 30 arcsec (0.5 pc) and 2 arcmin
(2 pc). These ejecta rings appear to be a common phenomenon of young
core-collapse remnants and may be associated with post-explosion input of
energy from plumes of radioactive 56Ni-rich ejecta that rise, expand, and
compress non-radioactive material. Our optical survey also encompassed Cas A's
faint outlying ejecta knots and exceptionally high-velocity NE and SW streams
of S-rich debris often referred to as `jets'. These outer knots, which exhibit
a chemical make-up suggestive of an origin deep within the progenitor star,
appear to be arranged in opposing and wide-angle outflows with opening
half-angles of approximately 40 degrees.Comment: 15 pages, 11 figures, accepted by ApJ, associated movie files can be
found at https://www.cfa.harvard.edu/~dmilisav
A Comparison of X-ray and Optical Emission in Cassiopeia A
Broadband optical and narrowband Si XIII X-ray images of the young Galactic
supernova remnant Cas A obtained over several decades are used to investigate
spatial and temporal correlations on both large and small scales. The data
consist of optical and near infrared ground-based and Hubble Space Telescope
images taken between 1951 and 2011, and X-ray images from Einstein, ROSAT, and
Chandra taken between 1979 and 2013. We find weak spatial correlations between
the remnant's emission features on large scales, but several cases of good
optical/X-ray correlations on small scales for features which have brightened
due to recent interaction with the reverse shock. We also find instances where:
(i) a time delay is observed between the appearance of a feature's optical and
X-ray emissions, (ii) displacements of several arcseconds between a feature's
X-ray and optical emission peaks and, (iii) regions showing no corresponding
X-ray or optical emissions. To explain this behavior, we propose a
inhomogeneous model for Cas A's ejecta consisting of small, dense optically
emitting knots (n ~ 10^(2-3)/cm^(3)) and a much lower density (n ~ 0.1 -
1/cm^(3)) diffuse X-ray emitting component often spatially associated with
optical emission knots. The X-ray emitting component is sometimes linked to
optical clumps through shock induced mass ablation generating trailing material
leading to spatially offset X-ray/optical emissions. A range of ejecta
densities can also explain the observed X-ray/optical time delays since the
remnant's 5000 km/s reverse shock heats dense ejecta clumps to temperatures
around 3x10^4 K relatively quickly which then become optically bright while
more diffuse ejecta become X-ray bright on longer timescales. Highly
inhomogeneous ejecta as proposed here for Cas A may help explain some of the
X-ray/opticalfeatures seen in other young core collapse SN remnants.Comment: 31 pages, 21 figures. Submitted to the Astrophysical Journal. Please
contact the corresponding author for higher resolution postscript versions of
the figures ([email protected]
Discovery of Extensive Optical Emission Associated with the X-ray Bright, Radio Faint Galactic SNR G156.2+5.7
We present wide-field Halpha images of the Galactic supernova remnant
G156.2+5.7 which reveal the presence of considerable faint Halpha line emission
coincident with the remnant's X-ray emission. The outermost Halpha emission
consists largely of long and thin (unresolved), smoothly curved filaments of
Balmer-dominated emission presumably associated with the remnant's forward
shock front. Patches of brighter Halpha emission along the western,
south-central, and northeastern regions appear to be radiative shocked ISM
filaments like those commonly seen in supernova remnants, with relatively
strong [O I] 6300,6364 and [S II] 6716,6731 line emissions.
Comparison of the observed Halpha emission with the ROSAT PSPC X-ray image of
G156.2+5.7 shows that the thin Balmer-dominated filaments lie along the
outermost edge of the remnant's detected X-ray emission. Brighter radiative
emission features are not coincident with the remnant's brightest X-ray or
radio regions. Areas of sharply weaker X-ray flux seen in the ROSAT image of
G156.2+5.7 appear spatially coincident with dense interstellar clouds visible
on optical and IRAS 60 and 100 micron emission images, as well as maps of
increased optical extinction. This suggests significant X-ray absorption in
these regions due to foreground interstellar dust, especially along the western
and southern limbs. The close projected proximity and alignment of the
remnant's brighter, radiative filaments with several of these interstellar
clouds and dust lanes hint at a possible physically interaction between the
G156.2+5.7 remnant and these interstellar clouds and may indicate a smaller
distance to the remnant than previously estimated.Comment: To appear in Monthly Notices of the Royal Astronomical Societ
A Late-Time Optical Detection of SN 1985L in NGC 5033
An apparent late-time optical recovery of SN 1985L (Type II-L) in the Sb galaxy NGC 5033 is presented and discussed. An Hα emission point source is found within 1\u27\u27 of both SN 1985L\u27s historically reported position 70\u27\u27 west and 55\u27\u27 north of NGC 5033\u27s center and its late-time, radio-measured position. This Hα source is not visible on V-band or narrow red continuum (7000 ± 125 Å) images, but is detected using a 6510 Å filter (FWHM = 30 Å). Its detection at 6510 Å can be attributed to blueshifted Hα emission because of a broad (±5000 km s-1) Hα line profile like that seen in late-time Type II-L spectra. The SN 1985L source has an estimated total Hα flux of (5 ± 1) × 10-16 ergs cm-2 s-1, making it, at a distance of 13 Mpc, about as luminous as the late-time Hα emission from SN 1970G. The presence of Hα emission from SN 1985L suggests that it has a spectrum similar to that of other comparably aged Type II-L supernovae, and further helps establish a late-time radio-optical link for this subclass of Type II events
An Optical Survey of Outlying Ejecta in Cassiopeia A: Evidence for a Turbulent, Asymmetric Explosion
A deep optical survey of the Cassiopeia A supernova remnant has revealed dozens of new emissionline ejecta knots out beyond the remnantÏs bright nebular shell. Most of the newly detected knots exhibit a 4500È 7500 A. spectrum dominated by [N II ] jj 6548,6583 line emissions. After accounting for possible decelerations, the estimated space velocities for about four dozen of these [N II ] knots suggest a nearly isotropic ^ 10,000 km s~1 ejection velocity. However, a small group along the southwestern limb show signi‹cantly higher velocities of up to 12,000 km s~1 . Over 20 outlying O] S emission knots were also discovered, mostly along the remnantÏs western limb. These knots have optical spectral properties like those seen in the main shellÏs metal-rich .. fast-moving knots ÏÏ but with much higher estimated space velocities of between 7600 and 12,600 km s~1 . Discovery of these knots means that the remnantÏs highest-velocity, O] S debris are not con‹ned to just the remnantÏs northeast .. jet.ÏÏ [S II ] jj 6716,6731 emissions dominate the spectra of these knots above an expansion velocity of 11,000 km s~1 . A few mixed emission knots,ÏÏ which show both strong nitrogen and sulfur line emissions, were also detected along the remnantÏs western rim. The properties of these outlying debris knots suggest a turbulent supernova expansion in which the innermost S-rich layers were ejected up through overlying material in certain regions, attaining ‹nal outward velocities greater than the starÏs N and He-rich surface layers. The detection of such high-velocity, sulfur-rich ejecta only along the remnantÏs northeast and southwest limbs further suggests an asymmetric expansion, possibly bipolar. A turbulent expansion may help explain the creation of the observed mixed emission knots. It is unclear, however, if mixed knots represent truly microscopically mixed debris or are simply small, comoving clusters of chemically distinct ejecta
Ejecta in SN 1006: The knotty issue
The 1988 IUE SWP observations of a faint sdOB star situated behind the remnant of the supernova of AD 1006 are presented. These spectra along with IUE spectra of the star taken between 1982 and 1986 provide a detailed look at the elemental composition and dynamical properties of the SN 1006 remnant. Over the 6 years there were no significant changes in the absorption features associated with the remnant at 1281, 1330, or 1420 A. While the lack of variability in these absorption lines makes it impossible to decide whether the ejecta is distributed smoothly or in knots, it is clear that the 1281 A feature is a blend, requiring either S II absorption redshifted at 6000 km/sec plus Si II 1260 at 5200 km/sec, or else 2 individual Si absorbing regions
The 2D Distribution of Iron Rich Ejecta in the Remnant of SN 1885 in M31
We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of
the remnant of Supernova 1885 (S And) which is observed in absorption against
the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II
absorption line images to previous HST absorption images of S And, of which the
highest quality and theoretically cleanest is Ca II H & K. Because the remnant
is still in free expansion, these images provide a 2D look at the distribution
of iron synthesized in this probable Type Ia explosion, thus providing insights
and constraints for theoretical SN Ia models. The Fe I images show extended
absorption offset to the east from the remnant's center as defined by Ca II
images and is likely an ionization effect due to self-shielding. More
significant is the remnant's apparent Fe II distribution which consists of four
streams or plumes of Fe-rich material seen in absorption that extend from
remnant center out to about 10,000 km/s. This is in contrast to the remnant's
Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at
1000 to 5000 km/s but which extends out to 12,500 km/s. The observed
distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent
with delayed detonation white dwarf models. The largely spherical symmetry of
the Ca-rich layer argues against a highly anisotropic explosion as might result
from a violent merger of two white dwarfs.Comment: 14 pages, 8 figures, and 1 table; revised to match ApJ published
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