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 versio