Kepler's Supernova Remnant Research Articles

Iron needles in supernova remnants?

It has been suggested by Dwek (2004) that iron needles could explain the submillimetre emission from the Cas A supernova remnant (SNR) with only a very small total mass. We investigate whether a similar model holds for the Kepler supernova remnant, and find that its emission could indeed be explained by a dust mass of less than 10^-2 M_sun dependent on the axial ratio (l/a) of the needles - which we constrain to be less than 700. But the implied needle model for Kepler is inconsistent with that suggested for Cas A since either the needles would have to have a resistivity one or two orders of magnitude greater than those in Cas A or the electron density in Kepler's shocked plasma must be 40 times greater than suggested by X-ray observations. An additional problem with the needle model is that the implied thickness of the needles seems to be implausibly small, if the emission properties are calculated under the usual approximations.

XMM-Newtonobservation of Kepler's supernova remnant

We present the first results coming from the observation of Kepler's supernova remnant obtained with the EPIC instruments on board the XMM-Newton satellite. We focus on the images and radial profiles of the emission lines (Si K, Fe L, Fe K) and of the high energy continuum. Chiefly, the Fe L and Si K emission-line images are generally consistent with each other and the radial profiles show that the Si K emission extends to a larger radius than the Fe L emission (distinctly in the southern part of the remnant). Therefore, in contrast to Cas A, no inversion of the Si- and Fe-rich ejecta layers is observed in Kepler. Moreover, the Fe K emission peaks at a smaller radius than the Fe L emission, which implies that the temperature increases inwards in the ejecta. The 4–6 keV high energy continuum map shows the same distribution as the asymmetric emission-line images except in the southeast where there is a strong additional emission. A two color image of the 4–6 keV and 8–10 keV high energy continuum illustrates that the hardness variations of the continuum are weak all along the remnant except in a few knots. The asymmetry in the Fe K emission-line is not associated with any asymmetry in the Fe K equivalent width map. The Si K maps lead to the same conclusions. Hence, abundance variations do not cause the north-south brightness asymmetry. The strong emission in the north may be due to overdensities in the circumstellar medium. In the southeastern region of the remnant, the lines have a very low equivalent width and the X-ray emission is largely nonthermal.

Cold Dust in Kepler's Supernova Remnant

The timescales to replenish dust from the cool winds of asymptotic giant branch stars are believed to be greater than the timescales for dust destruction. In high-redshift galaxies, this problem is further compounded as the stars take longer than the age of the universe to evolve into the dust production stages. To explain these discrepancies, dust formation in supernovae (SNe) is required to be an important process, but until recently dust in supernova remnants (SNRs) has only been detected in very small quantities. We present the first submillimeter observations of cold dust in Kepler's SNR using the Submillimeter Common-User Bolometric Array. A two-component dust temperature model is required to fit the spectral energy distribution with Twarm ~ 102 K and Tcold ~ 17 K. The total mass of dust implied for Kepler is ~1 M—1000 times greater than previous estimates. Thus SNe, or their progenitors, may be important dust formation sites.

High resolution spectroscopy of Balmer-dominated shocks in the RCW 86, Kepler and SN 1006 supernova remnants

We report results from high resolution optical spectroscopy of three non-radiative galactic supernova remnants, RCW 86, Kepler's supernova remnant and SN 1006. We have measured the narrow component Hα line widths in Balmer-dominated filaments in RCW 86 and SN 1006, as well as the narrow component width in a Balmer-dominated knot in Kepler's SNR. The narrow component line widths measured in RCW 86 and Kepler's SNR show FWHM of km s-1, similar to what has been seen in other Balmer-dominated remnants. Of the remnants in our sample, SN 1006 is the fastest shock (~3000 km s-1). The narrow component Hα and Hβ lines in this remnant have a FWHM of merely 21 km s-1. Comparing the narrow component widths measured in our sample with those measured in other remnants shows that the width of the narrow component does not correlate in a simple way with the shock velocity. The implications for the pre-heating mechanism responsible for the observed line widths are discussed.

Radio Spectral Index Variations and Physical Conditions in Kepler’s Supernova Remnant

A new epoch of VLA measurements of Kepler's supernova remnant (SNR) was obtained to make accurate measurements of the radio spectral index variations and polarization. We have compared these new radio images with Hα, infrared (IR), and X-ray data to better understand the three-dimensional structure and dynamics of Kepler's SNR and to better understand the physical relationships between the various nonthermal and thermal plasmas. Spatial variations in the radio spectral index from -0.85 to -0.6 are observed between 6 and 20 cm. The mean spectral index is -0.71. The mean percent polarization is 3.5% at 20 cm and 6% at 6 cm. There is a strong correspondence between the radial and azimuthal profiles of the radio, X-ray, Hα, and IR emission in different locations around the remnant, although there is no single, global pattern. Spectral tomography shows that the flat- and steep-spectrum radio emissions have distinct structures. The flat-spectrum radio emission is found at either a larger radius than or coincident with the steep-spectrum emission. We interpret these spectral components as tracing forward- and reverse-shocked material, respectively. The flat-spectrum radio emission can alternatively be interpreted as the bow shocked material (reshocked by the forward shock) from the progenitor's motion through the interstellar medium. The Hα and IR images are very similar. Their leading edges are coincident and are either in front of or coincident with the leading edges of the X-ray and radio emission. The X-ray emission matches the Hα and IR emission in places and, in other places, traces the steep-spectrum radio emission. In the north, there is also an anticorrelation in the azimuthal profiles around the remnant of the flat-spectrum radio emission and the thermal X-ray, Hα, and IR emissions. We suggest that this could be due to a relative weakening of the particle acceleration at the forward shock due to Alfven wave damping in regions of high density.

What Next for the Likely Presupernova HD 179821?

We have used the Owens Valley Radio Observatory Millimeter Array to obtain a map of the J = 1→0 CO emission from the circumstellar shell around HD 179821, a highly evolved G-type star that will probably explode as a supernova in the next 105 yr. Very approximately, the gas presents as a circular ring with an inner diameter of 395, an outer diameter of ~12'', and azimuthal variations in the CO brightness of a factor of about 2. Until about 1600 years ago, the star was a red hypergiant, losing about 3 × 10-4 M☉ yr-1 at an average outflow speed of 32 km s-1. We propose that when HD 179821 explodes as a supernova, it may resemble Kepler's supernova remnant, and thus some of the anisotropies in supernova remnants may be intrinsic. If the factors that cause the anisotropic mass loss in HD 179821 persist until the moment when the star explodes as a supernova, the newly born pulsar may receive a momentum kick, leading to a space motion of close to 700 km s-1. Independent of the angular asymmetries, the radially detached shell around HD 179821 may be representative of environments that produce dust echoes from gamma-ray bursts.

Dust in the Tycho, Kepler and Crab supernova remnants

SuperNova Remnants (SNR) have been extensively studied in radio, X-rays and optical, but barely in the InfraRed (IR). From IRAS observations, SNR are known to be IR emitters, but the origin of the emission is difficult to assess because of the limited angular and spectral resolution of IRAS observations. ISO follow-up observations of the Cassiopeia-A SNR have shown that the mid-IR radiation from this remnant was dominated by thermal emission from silicate condensates made from SN material. These condensates constitute a probe which can provide unique information about element mixing inside a SN. In this paper, we present ISOCAM observations of the three other young SNR's known in our galaxy: the Kepler SNR, the Tycho SNR and the Crab Nebula. The emission observed from the Kepler SNR is dominated by dust thermal emission. The dust at the origin of the IR emission is circumstellar, not from SN condensates. Astronomical silicates, collisionally heated to a temperature of 107 K, can account for both the mid-IR ISO data and the IRAS data. The IR emission from Tycho is probably also emitted by circumstellar or interstellar dust. In order to reproduce both the mid-IR ISO data and the IRAS data, a model with two dust components, one at a temperature of 107 K and the other at 55 K, is needed. The mid-IR emission from the Crab is dominated by synchrotron radiation; no dust is detected.

Near-Infrared Spectroscopy of the Cassiopeia A and Kepler Supernova Remnants

Near-infrared spectra (0.95 - 2.4 micron) of the Cassiopeia A and Kepler supernova remnants (SNRs) are presented. Low-dispersion (R = 700) spectra were obtained for five bright fast-moving ejecta knots (FMKs) at two locations on the main shell and for three bright circumstellar knots (QSFs) near the southwest rim of Cas A. The main shell FMKs in Cas A exhibit a sparse near-infrared spectrum dominated by [S II] 1.03 micron emission with a handful of other, fainter emission lines. Among these are two high-ionization silicon lines, [Si VI] 1.96 micron and [Si X] 1.43 micron, which have been detected in AGNs and novae but never before in a supernova remnant. The near-infrared spectra of circumstellar QSFs in Cas A show a much richer spectrum, with strong He I 1.083 micron emission and over a dozen bright [Fe II] lines. Observed [Fe II] line ratios indicate electron densities of 5 - 9 * 10^4 cm^-3 in the QSFs. The Cas A QSF data are quite similar to the observed spectrum of a bright circumstellar knot along the northwest rim of the Kepler SNR, which also shows strong He I and [Fe II] emission with a measured electron density of 2.5 - 3 * 10^4 cm^-3. Finally, we present J- and K-band images of Cas A. The K-band image shows faint diffuse emission which has no optical or mid-infrared counterpart but is morphologically similar to radio continuum maps and may be infrared synchrotron radiation.

The Expansion of the X-ray Remnant of Tycho’s Supernova (SN 1572)

Two ROSAT high-resolution images separated by nearly 5 years have been used to determine the expansion of the X-ray remnant of Tycho's supernova (SN 1572). The current expansion rate averaged over the entire remnant is 0.124% ± 0.011% yr-1, which, when combined with the known age of the remnant, determines the mean expansion parameter m, defined as R ∝ tm, to be 0.54 ± 0.05. There are significant radial and azimuthal variations of the X-ray expansion rate. The radial expansion in particular shows highly significant evidence for the more rapid expansion of the forward blast wave as compared to the reverse-shocked ejecta, an effect that has not been seen previously. The expansion parameter varies from m = 0.71 ± 0.06 at the outermost edge of Tycho's supernova remnant (SNR) to a value of m = 0.34 ± 0.10 on the inside edge of the bright rim of emission. These values are consistent with the rates expected for a remnant with constant density ejecta evolving into a uniform interstellar medium during the ejecta-dominated phase of evolution. Based on the size, age, and X-ray expansion rates, I obtain values for the explosion energy and ambient density of E ≈ × 1050 ergs and n0 ≈ 0.3-0.6 cm-3. As is also the case for Cas A and Kepler's SNR, the X-ray expansion rate of Tycho's SNR appears to be significantly higher than the radio expansion rate. In the case of Tycho's SNR, however, the difference between radio and X-ray expansion rates is clearly associated with the motion of the forward shock.

Confirmation of three candidate Galactic supernova remnants from GMRT observations

We report 327-MHz observations of three large (>15 arcmin) candidate supernova remnants (SNRs) at high Galactic latitudes using the Giant Metrewave Radio Telescope (GMRT). These objects were proposed by Duncan et al. as candidate SNRs in the Parkes 2.4-GHz survey. We detect extended 327-MHz emission in all three fields. G356.2+4.5 has a well-resolved shell of emission. This field also contains a 32-mJy pulsar situated at a distance of 1.4 kpc as derived from the dispersion measure of the pulsar. The field of G358.0+3.8 is highly confused and, although we confirm the presence of a partial ring, it has a lower signal-to-noise ratio detection. G004.8+6.2 (formerly G4.5+6.2) is located approximately 40 arcmin away from Kepler's SNR. Apart from GMRT observations of this field, this SNR lies in the field of view of a Very Large Array (VLA) D-array observation at 325 MHz and we detect a 17×18 arcmin SNR, possibly of shell morphology. All these fields show clear, well-resolved shells in the National Radio Astronomy Observatory/VLA Sky Survey (NVSS) maps, which are also presented.

Model of ASCA X-ray spectrum of Kepler's SNR

We report the results of Kepler's supernova remnant (SNR) observed with ASCA. We obtained the X-ray spectrum of Kepler's SNR in the energy range between 0.5 keV and 10 keV, clearly detected many emission lines from the heavy elements. The spectrum was not reproduced by a single temperature CIE and NEI model. Therefore, we constructed a realistic spectral model considering the SNR evolution; the Sedov and the Chevalier model. The X-ray spectrum of Kepler's SNR was not reproduced by the Sedov model, but well by the Chevalier model, except the Fe-K line blends. The emission from the ejecta heated by the reverse shock dominates that from the ISM heated by the blast wave. Kepler's SNR is not in the Sedov phase, but in the free-expansion phase. The abundance of the ejecta strongly suggests that Kepler's SN is a SN Ia. However, since the Fe-K line blends could not be reproduced well, another component producing the Fe-K line blends is needed. The Fe-K line emission is well produced by the additional iron component. This component must have a relatively higher temperature and a lower ionization timescale than these of the main ejecta. The iron component must be an iron dominant plasma which is a fossil of the iron ejecta of the SN Ia explosion.

A New Determination of the Distance to Kepler’s Supernova Remnant

Using the Very Large Array, H I observations of Kepler's supernova remnant (SN 1604, 3C 358) have been carried out with an angular resolution of approximately 15'' and a velocity resolution of 1.3 km s-1. The distance to this historical supernova remnant (SNR; diameter ~3') has been controversial, with estimates ranging from a few kiloparsecs to 12 kpc. Based on a weak H I absorption feature at +21.3 km s-1 seen in the new data, a lower limit of 4.8 ± 1.4 kpc can be derived. No prominent interstellar H I features are detected near Kepler's SNR, indicating that the evolution of the remnant has been influenced by the circumstellar medium, while the interstellar medium seems to have had negligible effect on the expansion process. At a velocity of +21.3 km s-1, emission from an H I cloud to the east of the SNR is detected, which may be physically associated with the remnant of SN 1604, based on morphological considerations. An upper limit of 6.4 kpc to the distance can be derived based on the lack of H I absorption at a velocity of +50 km s-1, where extended H I emission is detected.

Determination of the thermal and non-thermal emissions in the X-ray spectrum of Kepler's supernova remnant

The objectives of this study is, by combining ASCA and XTE data, to search for a non thermal emission in the spectrum of Kepler's supernova remnant and to derive a consistent model of the thermal emission by using hydrodynamical models coupled to non equilibrium ionization calculation.

Determination of the thermal and non-thermal emissions in the X-ray spectrum of Kepler's supernova remnant

Determination of the thermal and non-thermal emissions in the X-ray spectrum of Kepler's supernova remnant

ASCA Observation of Kepler's Supernova Remnant

We report the results of Kepler's supernova remnant (SNR) observed with ASCA. We clearly detected many emission lines from heavy elements on the SIS spectrum. Since we could not fit the data with a simple non-equilibrium ionization (NEI) hot-plasma model, we applied realistic SNR models employing either the Sedov model or the Chevalier model. As a result, the spectrum was not reproduced by the Sedov model, but was well-reproduced by the Chevalier model, except for the Fe-K line blends. The emission from the ejecta heated by reverse shock dominates that from the interstellar matter heated by the fore shock. The relative abundances of the ejecta strongly suggest that Kepler's SN is a SN la. However, the Fe-K line blends could not be reproduced well by only the Chevalier model from an astrophysical point of view. We found that the Fe-K line emission was well produced by an additional iron component. This component must have a relatively higher temperature and a lower ionization time scale than those of the ejecta component. This additional iron component may result from mixing of the inner region. This must be an iron-dominant plasma which is a fossil of the SN la explosion.

On the X-ray spectrum of Kepler's supernova remnant

We have devised a method to do nonequilibrium ionization calculations on the results of two-dimensional hydrodynamical simulations, based on the algorithm of Hughes & Helfand (1985). We have calculated the ionization structure and X-ray emission for a two-dimensional numerical hydrodynamical simulation for the remnant of Kepler's supernova (SN); the hydrodynamical model was presented in a previous paper. In this model, the progenitor of Kepler's SN is assumed to have been a massive runaway star ejected from the Galactic plane. In its red supergiant stage, its dense stellar wind was distorted and compressed into a bow shock by the ram pressure of the tenuous interstellar medium. The subsequent interaction of the supernova ejecta with this asymmetric circumstellar matter produced a strongly asymmetric supernova remnant (SNR). In this paper, we present calculated X-ray spectra for this hydrodynamical model. A comparison with observations implies a moderate overabundance of Fe in Kepler's SNR (only 50% larger than its cosmic value), in contrast to a large (6 to 15) Fe overabundance derived previously. However, we confirm earlier conclusions that Si and S abundances are 2 to 3 times solar. These modest enhancements of Si, S, and Fe may be attributed either to heavy-element enriched SN ejecta or to the initial chemical abundances of the SN progenitor, which originated in the metal-rich inner Galaxy. The comparison of our models with the observed spectra confirm theoretical predictions that moderate electron heating occurs at strong collisionless shock fronts, with the implied electron/mean temperature ratio of approximately 0.5.

Electron acceleration in Tycho's and Kepler's supernova remnants - Spectral evidence of Fermi shock acceleration

First model synchrotron spectra calculated with a self-consistent nonlinear shock model of first order Fermi acceleration are presented and compared with the observed radio spectra of Tycho's and Kepler's SNR. Excellent agreement is obtained, and the correct mean spectral indices of about -0.64 are easily reproduced. The model spectra are slightly concave, with hardening toward higher energies, and there is evidence for such an effect in the data, allowing the mean magnetic field strength to be estimated in each remnant. Improvements in both theory and observation could allow accurate values of magnetic fields to be inferred from sufficiently precise integrated synchrotron spectra.

Dynamics of Kepler's supernova remnant

Observations of Kepler's SNR have revealed a strong interaction with the ambient medium, far in excess of that expected at a distance of about 600 pc away from the Galactic plane where Kepler's SNR is located. This has been interpreted as a result of the interaction of supernova ejecta with the dense circumstellar medium (CSM). Based on the bow-shock model of Bandiera (1985), we study the dynamics of this interaction. The CSM distribution consists of an undisturbed stellar wind of a moving supernova progenitor and a dense shell formed in its interaction with a tenuous interstellar medium. Supernova ejecta drive a blast wave through the stellar wind which splits into the transmitted and reflected shocks upon hitting this bow-shock shell. We identify the transmitted shock with the nonradiative, Balmer-dominated shocks found recently in Kepler's SNR. The transmitted shock most probably penetrated the shell in the vicinity of the stagnation point.

IMAGING OF KEPLER'S SUPERNOVA REMNANT

ABSTRACT It is shown that the effects of crowding on images of Kepler's supernova remnant, that were obtained with the 3.6-m CFHT, can be greatly reduced by digitally subtracting a scaled continuum image from a narrow-band H-alpha + forbidden N II image. Attention is drawn to a narrow emission filament that extends for 27 arcsec along the western edge of the optical remnant.

A detailed optical study of Kepler's supernova remnant

Optical CCD/interference filter imagery and long-slit CCD spectrophotometry are presented of the remnant of Kepler's supernova (SN 1604 A.D.) obtained with the 2.5 DuPont telescope at the Las Campanas Observatory. Substraction of a continuum image from the emission line image shows the full extent of the optical emission of the supernova remnant, which has both diffuse and knotty structures. Spectroscopy in the 4700-7000 A range confirms the presence of nonradiative, Balmer-dominated, shock emission in Kepler's remnant and shows this emission to be much more extensive than previously realized, extending to knotty structures as well as diffuse emission.