We performed Spitzer Infrared Spectrograph mapping observations covering nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing mid-infrared (5.5Y35 m) spectra every 5 00 Y10 00 . Gas lines of Ar, Ne, O, Si, S, and Fe, and dust continua were strong for most positions. We identify three distinct ejecta dust populations based on their continuum shapes. The dominant dust continuum shape exhibits a strong peak at 21 m. A line-free map of 21 m peak dust made from the 19Y23 m range closely resembles the [Ar ii], [O iv], and [Ne ii] ejecta-line maps, implying that dust is freshly formed in the ejecta. Spectral fitting implies the presence of SiO 2 , Mg protosilicates, and FeO grains in these regions. The second dust type exhibits a rising continuum up to 21 m and then flattens thereafter. This ''weak 21 m'' dust is likely composed of Al 2 O 3 and C grains. The third dust continuum shape is featureless with a gently rising spectrum and is likely composed of MgSiO 3 and either Al 2 O 3 or Fe grains. Using the least massive composition for each of the three dust classes yields a total mass of 0.020 M . Using the most massive composition yields a total mass of 0.054 M . The primary uncertainty in the total dust mass stems from the selection of the dust composition necessary for fitting the featureless dust as well as 70 m flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to explain the lower limit on the dust masses in high-redshift galaxies.

We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the entire extent of Cassiopeia A between 5-40 µm. Using infrared and Chandra X-ray Doppler velocity measurements, along with the locations of optical ejecta beyond the forward shock, we constructed a 3-D model of the remnant. The structure of Cas A can be characterized into a spherical component, a tilted thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all populating the thick disk plane. The Bright Ring in Cas A identifies the intersection between the thick plane/pistons and a roughly spherical reverse shock. The ejecta pistons indicate a radial velocity gradient in the explosion. Some ejecta pistons are bipolar with oppositely-directed flows about the expansion center while some ejecta pistons show no such symmetry. Some ejecta pistons appear to maintain the integrity of the nuclear burning layers while others appear to have punched through the outer layers. The ejecta pistons indicate a radial velocity gradient in the explosion. In 3-D, the Fe jet in the southeast occupies a "hole" in the Si-group emission and does not represent "overturning", as previously thought. Although interaction with the circumstellar medium affects the detailed appearance of the remnant and may affect the visibility of the southeast Fe jet, the bulk of the symmetries and asymmetries in Cas A are intrinsic to the explosion.

We introduce a million-second observation of the supernova remnant Cassiopeia A with the Chandra X-ray Observatory. The bipolar structure of the Si-rich ejecta (NE jet and SW counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A.

The distribution of elements produced in the innermost layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms NuSTAR observing campaign aimed at studying the supernova remnant Cassiopeia A (Cas A). We perform spatially resolved spectroscopic analyses of the 44 Ti ejecta, which we use to determine the Doppler shift and thus the three-dimensional (3D) velocities of the 44 Ti ejecta. We find an initial 44 Ti mass of (1.54±0.21) ×10 −4 M e , which has a present-day average momentum direction of 340°±15°projected onto the plane of the sky (measured clockwise from celestial north) and is tilted by 58°±20°into the plane of the sky away from the observer, roughly opposite to the inferred direction of motion of the central compact object. We find some 44 Ti ejecta that are clearly interior to the reverse shock and some that are clearly exterior to it. Where we observe 44 Ti ejecta exterior to the reverse shock we also see shock-heated iron; however, there are regions where we see iron but do not observe 44 Ti. This suggests that the local conditions of the supernova shock during explosive nucleosynthesis varied enough to suppress the production of 44 Ti by at least a factor of two in some regions, even in regions that are assumed to be the result of processes like α-rich freezeout that should produce both iron and titanium.

3C 397 is a radio and X-ray bright Galactic supernova remnant (SNR) with an unusual rectangular morphology. Our CO observation obtained with the Purple Mountain Observatory at Delingha reveals that the remnant is well confined in a cavity of molecular gas, and embedded at the edge of a molecular cloud (MC) at the local standard of rest systemic velocity of ∼ 32 km s −1 . The cloud has a column density gradient increasing from southeast to northwest, perpendicular to the Galactic plane, in agreement with the elongation direction of the remnant. This systemic velocity places the cloud and SNR 3C 397 at a kinematic distance of ∼ 10.3 kpc. The derived mean molecular density (∼ 10-30 cm −3 ) explains the high volume emission measure of the X-ray emitting gas. A 12 CO line broadening of the ∼ 32 km s −1 component is detected at the westmost boundary of the remnant, which provides direct evidence of the SNR-MC interaction and suggests multi-component gas there with dense (∼ 10 4 cm −3 ) molecular clumps. We confirm the previous detection of a MC at ∼ 38 km s −1 to the west and south of the SNR and argue, based on HI self-absorption, that the cloud is located in the foreground of the remnant.A list of 64 Galactic SNRs presently known and suggested to be in physical contact with environmental MCs is appended in this paper.