Core-collapse Supernova Remnants Research Articles

Nonthermal and thermal emission from the supernova remnant RX J1713.7-3946

A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is employed to investigate the properties of SNR RX J1713.7-3946. Observations of the non-thermal radio and X-ray emission spectra as well as the H.E.S.S. measurements of the very high energy gamma-ray emission are used to constrain the astronomical and CR acceleration parameters of the system. It is argued that RX J1713.7-3946 is a core collapse supernova (SN) of type II/Ib with a massive progenitor, has an age of ~1600 yr and is at a distance of ~1 kpc. It is in addition assumed that the CR injection/acceleration takes place uniformly across the shock surface for this kind of core collapse SNR. The theory gives a consistent description for all the existing observational data, including the non-detection of thermal X-rays and the spatial correlation of the X-ray and gamma-ray emission in the remnant. Specifically it is shown that an efficient production of nuclear CRs, leading to strong shock modification and a large downstream magnetic field strength B_d ~140 mkG can reproduce in detail the observed synchrotron emission from radio to X-ray frequencies together with the gamma-ray spectral characteristics as observed by the H.E.S.S. telescopes. The calculations are consistent with RX J1713.7-3946 being an efficient source of nuclear cosmic rays.

A DEEPCHANDRAOBSERVATION OF THE OXYGEN-RICH SUPERNOVA REMNANT 0540-69.3 IN THE LARGE MAGELLANIC CLOUD

Using our deep ~120 ks Chandra observation, we report on the results from our spatially-resolved X-ray spectral analysis of the "oxygen-rich" supernova remnant (SNR) 0540-69.3 in the Large Magellanic Cloud. We conclusively establish the nonthermal nature of the "arcs" in the east and west boundaries of the SNR, which confirms the cosmic-ray electron acceleration in the supernova shock (B ~ 20-140 microG). We report tentative evidence for Fe overabundance in the southern region close to the outer boundary of the SNR. While such a detection would be intriguing, the existence of Fe ejecta is not conclusive with the current data because of poor photon statistics and limited plasma models. If it is verified using deeper X-ray observations and improved plasma models, the presence of Fe ejecta, which was produced in the core of the supernova, near the SNR's outer boundary would provide an intriguing opportunity to study the explosive nucleosynthesis and the ejecta mixing in this young core-collapse SNR. There is no evidence of X-ray counterparts for the optical O-rich ejecta in the central regions of the SNR.

TYPING SUPERNOVA REMNANTS USING X-RAY LINE EMISSION MORPHOLOGIES

We present a new observational method to type the explosions of young supernova remnants (SNRs). By measuring the morphology of the Chandra X-ray line emission in seventeen Galactic and Large Magellanic Cloud SNRs with a multipole expansion analysis (using power ratios), we find that the core-collapse SNRs are statistically more asymmetric than the Type Ia SNRs. We show that the two classes of supernovae can be separated naturally using this technique because X-ray line morphologies reflect the distinct explosion mechanisms and structure of the circumstellar material. These findings are consistent with recent spectropolarimetry results showing that core-collapse SNe are intrinsically more asymmetric.

DENSE IRON EJECTA AND CORE-COLLAPSE SUPERNOVA EXPLOSION IN THE YOUNG SUPERNOVA REMNANT G11.2-0.3

We present the results of near-infrared spectroscopic observations of dense (≳103 cm−3) iron ejecta in the young core-collapse supernova remnant G11.2–0.3. Five ejecta knots projected to be close to its center show a large dispersion in their Doppler shifts: two knots in the east are blueshifted by more than 1000 km s-1, while three western knots have relatively small blueshifts of 20–60 km s-1. This velocity discrepancy may indicate that the western knots have been significantly decelerated or that there exists a systematic velocity difference among the knots. One ejecta filament in the northwestern boundary, on the other hand, is redshifted by ≳200 km s-1, while opposite filament in the southeastern boundary shows a negligible radial motion. Some of the knots and filaments have secondary velocity components, and one knot shows a bow shock-like feature in the velocity structure. The iron ejecta appear to be devoid of strong emission from other heavy elements, such as S, which may attest to the α-rich freezeout process in the explosive nucleosynthesis of the core-collapse supernova explosion close to its center. The prominent bipolar distribution of the Fe ejecta in the northwestern and southeastern direction, along with the elongation of the central pulsar wind nebula in the perpendicular direction, is consistent with the interpretation that the supernova exploded primarily along the northwestern and southeastern direction.

MEASURING DUST PRODUCTION IN THE SMALL MAGELLANIC CLOUD CORE-COLLAPSE SUPERNOVA REMNANT 1E 0102.2–7219

We present mid-infrared spectral mapping observations of the core-collapse supernova remnant 1E 0102.2-7219 in the Small Magellanic Cloud using the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. The remnant shows emission from fine structure transitions of neon and oxygen as well as continuum emission from dust. Comparison of the mid-IR dust emission with observations at x-ray, radio and optical wavelengths shows that the dust is associated with the supernova ejecta and is thus newly formed in the remnant. The spectrum of the newly formed dust is well reproduced by a model that includes 3x10^-3 solar masses of amorphous carbon dust at 70 K and 2x10^-5 solar masses of Mg2SiO4 (forsterite) at 145 K. Our observations place a lower limit on the amount of dust in the remnant since we are not sensitive to the cold dust in the unshocked ejecta. We compare our results to observations of other core-collapse supernovae and remnants, particularly Cas A where very similar spectral mapping observations have been carried out. We observe a a factor of ~10 less dust in E 0102 than seen in Cas A, although the amounts of amorphous carbon and forsterite are comparable.

A Catalog of Outer Ejecta Knots in the Cassiopeia A Supernova Remnant

Hubble Space Telescope images of the core-collapse supernova remnant Cassiopeia A are used to identify high-velocity knots of ejecta located outside the remnant's main emission shell of expanding debris. These ejecta fragments are found near or ahead of the remnant's forward shock front and mostly lie from 12000 to 30000 in radial distance from the remnant's center of expansion. Filter flux ratios when correlated with published spectra show that these knots can be divided into three emission classes: (1) knots dominated by [N II] lambda lambda 6548, 6583 emissions, ( 2) knots dominated by [O II] kk7319, 7330 emissions, and (3) knots displaying filter flux ratios suggestive of [ S II], [ O II], and [Ar III] lambda 7135 emission line strengths similar to the fast-moving knots'' (FMKs) found in the remnant's bright main shell. Of 1825 knots identified, 444 are strong [N II] emission knots, 192 are strong [O II] emission knots, and 1189 are FMK-like knots. In terms of location around the remnant, 972, 207, and 646 knots are found in the remnant's northeast jet, southwest jet, and non-jet regions, respectively. Assuming a distance of 3.4 kpc, derived knot transverse velocities based on proper motion measurements spanning a 9 month interval indicate maximum transverse expansion velocities for these three knot classes of 14,500, 13,500, and 11,500 km s(-1), respectively. We present a catalog of these outlying ejecta clumps comprising finding charts, epoch 2004.2 knot positions, proper motions, photometric filter fluxes, and estimated knot emission type, along with cross-references to previous knot identifications and data. This compilation represents a nearly tenfold increase in the number of outlying, high-velocity ejecta knots identified around the Cassiopeia A remnant.

Fallback and Black Hole Production in Massive Stars

The compact remnants of core collapse supernovae - neutron stars and black holes - have properties that reflect both the structure of their stellar progenitors and the physics of the explosion. In particular, the masses of these remnants are sensitive to the density structure of the presupernova star and to the explosion energy. To a considerable extent, the final mass is determined by the ``fallback'', during the explosion, of matter that initially moves outwards, yet ultimately fails to escape. We consider here the simulated explosion of a large number of massive stars (10 to 100 \Msun) of Population I (solar metallicity) and III (zero metallicity), and find systematic differences in the remnant mass distributions. As pointed out by Chevalier(1989), supernovae in more compact progenitor stars have stronger reverse shocks and experience more fallback. For Population III stars above about 25 \Msun and explosion energies less than $1.5 \times 10^{51}$ erg, black holes are a common outcome, with masses that increase monotonically with increasing main sequence mass up to a maximum hole mass of about 35 \Msun. If such stars produce primary nitrogen, however, their black holes are systematically smaller. For modern supernovae with nearly solar metallicity, black hole production is much less frequent and the typical masses, which depend sensitively on explosion energy, are smaller. We explore the neutron star initial mass function for both populations and, for reasonable assumptions about the initial mass cut of the explosion, find good agreement with the average of observed masses of neutron stars in binaries. We also find evidence for a bimodal distribution of neutron star masses with a spike around 1.2 \Msun (gravitational mass) and a broader distribution peaked around 1.4 \Msun.

The Transition Zone in Balmer‐dominated Shocks

We examine the structure of the postshock region in supernova remnants (SNRs). The transition zone is set up by charge transfer and ionization events between atoms and ions and has a width ~(1015 cm-2)n, where n0 is the total preshock density (including both atoms and ions). For Balmer-dominated SNRs with shock velocity vs 1000 km s-1, the Rankine-Hugoniot conditions for ion velocity and temperature are obeyed instantly, leaving the full width at half-maximum (FWHM) of the broad Hα line versus vs relation intact. However, the spatial variation in the postshock densities is relevant to the problem of Lyα resonant scattering in young, core-collapse SNRs. Both two- (preshock atoms and ions) and three-component (preshock atoms, broad neutrals, and ions) models are considered. We compute the spatial emissivities of the broad (ξb) and narrow (ξn) Hα lines; a calculation of these emissivities in SN 1006 is in general agreement with the computed ones of Raymond and coworkers. The (dimensionless) spatial shift, Θshift, between the centroids of ξb and ξn is unique for a given shock velocity and fion, the preshock ion fraction. Measurements of Θshift can be used to constrain n0.

Feii] and H2Filaments in the Supernova Remnant G11.2−0.3: Supernova Ejecta and Presupernova Circumstellar Wind

We present the results of near-infrared imaging and spectroscopic observations of the young core-collapse supernova remnant (SNR) G11.2-0.3. In the [Fe II] 1.644 μm image, we first discover long, clumpy [Fe II] filaments within the radio shell of the SNR, together with some faint, knotty features in the interior of the remnant. The filaments are thick and roughly symmetric with respect to the northeast-southwest elongation axis of the central pulsar wind nebula. We have detected several [Fe II] lines and a H I Brγ line toward the peak position of the bright southeastern [Fe II] filament. The derived extinction is large (AV = 13 mag), and it is the brightest [Fe II] 1.644 μm filament detected toward SNRs to date. By analyzing two [Fe II] 1.644 μm images obtained 2.2 yr apart, we detect a proper motion corresponding to an expansion rate of 0.035'' ± 0.013'' yr-1 (830 ± 310 km s-1). In addition to the [Fe II] features, we also discover two small H2 2.122 μm filaments. One is bright and along the southeastern boundary of the radio shell, while the other is faint and just outside its northeastern boundary. We have detected the H2 (2-1) S(3) line toward the former filament and derive an excitation temperature of 2100 K. We suggest that the H2 filaments are dense clumps in a presupernova circumstellar wind swept up by the SNR shock, while the [Fe II] filaments are probably composed of both shocked wind material and shocked supernova (SN) ejecta. The distribution of [Fe II] filaments may indicate that the SN explosion in G11.2-0.3 was asymmetric, as in Cassiopeia A. Our results support the suggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting with a dense red supergiant wind.

Dust Destruction in Fast Shocks of Core-Collapse Supernova Remnants in the Large Magellanic Cloud

We report observations with the Multiband Imaging Photometer for Spitzer of four supernova remnants (SNRs) believed to be the result of core-collapse supernovae: N132D (0525–69.6), N49B (0525–66.0), N23 (0506–68.0), and 0453–68.5. All four of these SNRs were detected in whole at 24 mm and in part at 70 mm. Comparisons with Chandra broadband X-ray images show an association of infrared (IR) emission with the blast wave. We attribute the observed IR emission to dust that has been collisionally heated by electrons and ions in the hot, X-ray–emitting plasma, with grain size distributions appropriate for the LMC and the destruction of small grains via sputtering by ions. As with our earlier analysis of Type Ia SNRs, models can reproduce observed 70 mm/ 24 mm flux ratios only if effects from sputtering are included, destroying small grains. We calculate the mass of dust swept up by the blast wave in these remnants, and we derive a dust-to-gas mass ratio of several times less than the often assumed value of 0.25% for the LMC. We believe that one explanation for this discrepancy could be porous (fluffy) dust grains. Subject headings: dust, extinction — Magellanic Clouds — supernova remnants

Exploring the Kinematics of the Oxygen‐rich Supernova Remnant G292.0+1.8: Ejecta Shells, Fast‐moving Knots, and Shocked Circumstellar Material

We present the results of an in-depth optical study of the core-collapse supernova remnant G292.0+1.8 using the Rutgers Fabry-Perot (RFP) imaging spectrometer. Our observations provide a detailed picture of the supernova remnant in the emission lines of [O III] λ5007, Hα, and [N II] λ6548. The [O III] Fabry-Perot scans reveal a bright crescent-shaped spur of previously known high-velocity (Vradial ~ 1500 km s-1) O-rich ejecta located on the eastern side of the remnant. The spur consists of a semicoherent structure of mostly redshifted material, along with several clumps that have apparently broken out of the more orderly shell-like expansion. The high-velocity (600 km s-1) component of the spur also displays a scalloped morphology characteristic of Rayleigh-Taylor instabilities. We also find a large number of fast-moving knots (FMKs) of O-rich ejecta undetected in prior photographic plate images and similar to features seen in Cas A. The FMKs are distributed sparsely in the interior of G292.0+1.8 and are seen mostly in blueshifted emission out to Vradial ≈ -1700 km s-1. The position-velocity distribution of the FMKs can be kinematically described as a shell 34 in radius expanding at a velocity of 1700 km s-1. Another feature apparent in the [O III] scans is an equatorial belt consisting of both a barlike structure at zero radial velocity and a clumpy, high-velocity ejecta component seen in projection along the line of sight. Portions of the zero-velocity bar are spatially well correlated with a similar structure seen in the Chandra X-ray image of G292.0+1.8. The bar is also detected in our Hα RFP images at zero radial velocity, providing further evidence that this structure is of circumstellar origin. We find that the optical and X-ray properties of the bar are consistent with incomplete (partially radiative) shocks in material of moderate densities. There are also a number of faint, elongated structures seen in Hα at zero radial velocity across the interior of G292.0+1.8 that lack [O III] and X-ray counterparts. These filaments may be low-density H I clouds photoionized by hard radiation from the interior of the remnant. Overall, these results suggest that G292.0+1.8 is currently interacting with a low-density environment. We find no evidence for high-velocity Hα or [N II] emission over the dynamical range sampled by the RFP. Assuming a distance of 6 kpc for G292.0+1.8, we estimate a kinematic age of (3000-3400)d6 yr for this remnant.

Clump Development by the Nickel Bubble Effect in Supernovae

We used one-dimensional radiative-transport radiation hydrodynamical (RHD) simulations to investigate the formation of clumping in freely expanding supernova ejecta due to the radioactive heating from the 56Ni → 56Co → 56Fe decay sequence. The heating gives rise to an inflated Ni bubble, which induces a forward shock that compresses the outer ambient gas into a shell. The radiative energy deposited by the radioactivity leaks out across the shock by radiative diffusion, and we investigate its effect on the evolution of the ejecta structure. Compared to the hydrodynamical (HD) adiabatic approximation with γ = 4/3, the preshock gas becomes accelerated by the radiation outflow. The shock is thus weakened and the shell becomes broader and less dense. The thickness of the shell takes up 4% of the radius of the bubble, and the structure of the shell can be approximately described by a self-similar solution. We compared the properties of the shell components with those of the ejecta clumps indicated by our previous HD simulations for the interaction of clumps with the outer supernova remnant. The high density contrast across the shell, χ ~ 100, is compatible with that of ejecta clumps as indicated for Tycho's knots, but there is insufficient dense gas to cause a pronounced protrusion on the outline of a core-collapse supernova remnant, like the bullets in the Vela remnant.

Supernovae, Rotation, and Bipolar Explosions

In this paper, we discuss the possible role of rotation in supernova blast energetics and morphology, and speculate on the origin of Cas A’s and SN1987A’s ejecta fields. Two “explosive” phenomena may be associated with most core collapses, the neutrinodriven supernova itself and an underenergetic jet-like ejection that follows. The latter may be a magnetic wind that easily penetrates the debris created by the much more energetic supernova. We speculate that many core-collapse supernova remnants should have sub-dominant jet-like features. In Cas A, we associate this sub-dominant collimated wind with the “jet/counter-jet” structure observed. We suggest that the actual Cas A explosion itself is at nearly right angles to this jet, along a rotation axis that coincides with the bulk of the ejecta, the iron lobes, and the putative direction of motion of the point source. It may be that when rotation becomes sufficiently rapid that the strong-neutrinodriven-supernova/weak-jet duality switches to a strong-MHD-jet scenario that might be associated with hypernovae, and in some cases GRBs. Finally, we present a calculation using a new 2D multi-group, flux-limited radiation/hydrodynamics code we have recently developed for the simulation of core-collapse supernovae. We discuss the rotation-induced anisotropy in the neutrino radiation field, neutrino heating, and the neutrino flux vectors and speculate on rotation’s possible role in the supernova mechanism. ∗ We acknowledge discussions with Todd Thompson, Jeremiah Murphy, Casey Meakin, Itamar Lichtenstadt, and Moath Jarrah. Support for this work is provided in part by the Scientific Discovery through Advanced Computing (SciDAC) program of the DOE, grant number DE-FC02-01ER41184. In addition, we thank Jeff Fookson and Neal Lauver of the Steward Computer Support Group for their invaluable help with the local Beowulf cluster and acknowledge the use of the NERSC/LBNL/seaborg and ORNL/CCS/cheetah machines.

An Optical Survey of Supernova Remnants in M83

Observations of the face-on spiral galaxy M83 (NGC 5236) performed at the Cerro Tololo Inter-American Observatory in Chile have yielded a catalog of optical supernova remnant (SNR) candidates. These observations were performed with the 4 m Blanco telescope and a prime focus CCD imaging system using narrowband interference filters centered on the light of [S II], Hα, [O III], and red and blue continuum bands. Based on strong relative [S II] : Hα emission, 71 emission nebulae have been identified as SNR candidates. Positions and Hα fluxes of the candidates are presented. Follow-up spectra of 25 of the SNR candidates, also performed at CTIO, have confirmed many of the SNR identifications, although the spectra of a few objects are discrepant, perhaps because of inaccurate aperture placement. In addition, the low mean excitation of M83 H II regions has allowed a separate search for young oxygen-dominated (core collapse) SNRs similar to Cas A in our Galaxy, using [O III] : Hα. This search found a number of the same objects as the [S II] : Hα search, indicating that many of these SNRs have shock velocities in excess of 100 km s-1. However, no bona fide young core-collapse SNRs were detected with this technique, with the possible exception of the independent recovery of SN 1957D, which had been seen previously. We have also attempted to identify optical counterparts for the six historical supernovae that have occurred in M83. Except for SN 1957D, none of the historical supernovae have been detected by this survey. We compare our SNR candidate list against the Chandra X-ray source list of Soria and Wu and identify 15 X-ray sources as likely SNRs, based on positional coincidence within 1''. The sources identified have hardness ratios that are soft compared to the general X-ray source population in M83.

Bullets in a Core‐Collapse Supernova Remnant: The Vela Remnant

We use two-dimensional hydrodynamical simulations to investigate the properties of dense ejecta clumps (bullets) in a core-collapse supernova remnant, motivated by the observation of protrusions probably caused by clumps in the Vela supernova remnant. The ejecta, with an inner flat and an outer steep power-law density distribution, were assumed to freely expand into an ambient medium with a constant density, ~0.1 H atoms cm-3 for the case of Vela. At an age of 104 yr, the reverse shock front is expected to have moved back to the center of the remnant. Ejecta clumps with an initial density contrast χ ~ 100 relative to their surroundings are found to be rapidly fragmented and decelerated. In order to cause a pronounced protrusion on the blast wave, as observed in the Vela remnant, χ ~ 1000 may be required. In this case, the clump should be near the inflection point in the ejecta density profile, at an ejecta velocity ~3000 km s-1. These results apply to moderately large clumps; smaller clumps would require an even larger density contrast. Clumps can create ring structure in the shell of the Vela remnant, and we investigate the possibility that RX J0852-4622, an apparent supernova remnant superposed on Vela, is actually part of the Vela shell. Radio observations support this picture, but the possible presence of a compact object argues against it. The Ni bubble effect or compression in a pulsar wind nebula are possible mechanisms to produce the clumping.