Kepler's SNR Research Articles

A study of Kepler supernova remnant: angular power spectrum estimation from radio frequency data

ABSTRACT Supernova remnants (SNRs) have a variety of overall morphology as well as rich structures over a wide range of scales. Quantitative study of these structures can potentially reveal fluctuations of density and magnetic field originating from the interaction with ambient medium and turbulence in the expanding ejecta. We have used 1.5 GHz (L band) and 5 GHz (C band) VLA data to estimate the angular power spectrum Cℓ of the synchrotron emission fluctuations of the Kepler SNR. This is done using the novel, visibility-based, Tapered Gridded Estimator of Cℓ. We have found that, for ℓ = (1.9–6.9) × 104, the power spectrum is a broken power law with a break at ℓ = 3.3 × 104, and power-law index of −2.84 ± 0.07 and −4.39 ± 0.04 before and after the break, respectively. The slope −2.84 is consistent with 2D Kolmogorov turbulence and earlier measurements for the Tycho SNR. We interpret the break to be related to the shell thickness of the SNR (0.35 pc) which approximately matches ℓ = 3.3 × 104 (i.e. 0.48 pc). However, for ℓ > 6.9 × 104, the estimated Cℓ of L band is likely to have dominant contribution from the foregrounds while for C band the power-law slope −3.07 ± 0.02 is roughly consistent with 3D Kolmogorov turbulence like that observed at large ℓ for Cas A and Crab SNRs.

Type Ia supernova remnants: shaping by iron bullets

Using 2D numerical hydrodynamical simulations of Type Ia supernova remnants (SNR Ia) we show that iron clumps few times denser than the rest of the SN ejecta might form protrusions in an otherwise spherical SNR. Such protrusions exist in some SNR Ia, e.g. SNR 1885 and Tycho. Iron clumps are expected to form in the deflagration to detonation explosion model. In SNR Ia where there are two opposite protrusions, termed ‘ears’, such as Kepler's SNR and SNR G1.9+0.3, our scenario implies that the dense clumps, or iron bullets, were formed along an axis. Such a preferred axis can result from a rotating white dwarf progenitor. If our claim holds, this offers an important clue to the SN Ia explosion scenario.

SPITZEROBSERVATIONS OF THE TYPE IA SUPERNOVA REMNANT N103B: KEPLER'S OLDER COUSIN?

We report results from Spitzer observations of SNR 0509-68.7, also known as N103B, a young Type Ia supernova remnant in the Large Magellanic Cloud that shows interaction with a dense medium in its western hemisphere. Our images show that N103B has strong IR emission from warm dust in the post-shock environment. The post-shock gas density we derive, 45 cm$^{-3}$, is much higher than in other Type Ia remnants in the LMC, though a lack of spatial resolution may bias measurements towards regions of higher than average density. This density is similar to that in Kepler's SNR, a Type Ia interacting with a circumstellar medium. Optical images show H$\alpha$ emission along the entire periphery of the western portion of the shock, with [O III] and [S II] lines emitted from a few dense clumps of material where the shock has become radiative. The dust is silicate in nature, though standard silicate dust models fail to reproduce the "18 $\mu$m" silicate feature that peaks instead at 17.3 $\mu$m. We propose that the dense material is circumstellar material lost from the progenitor system, as with Kepler. If the CSM interpretation is correct, this remnant would become the second member, along with Kepler, of a class of Type Ia remnants characterized by interaction with a dense CSM hundreds of years post-explosion. A lack of N enhancement eliminates symbiotic AGB progenitors. The white dwarf companion must have been relatively unevolved at the time of the explosion.

THE ORIGIN OF KEPLER'S SUPERNOVA REMNANT

It is now well established that Kepler's supernova remnant is the result of a Type Ia explosion. With an age of 407 years, and an angular diameter of ~ 4', Kepler is estimated to be between 3.0 and 7.0 kpc distant. Unlike other Galactic Type Ia supernova remnants such as Tycho and SN 1006, and SNR 0509-67.5 in the Large Magellanic Cloud, Kepler shows evidence for a strong circumstellar interaction. A bowshock structure in the north is thought to originate from the motion of a mass-losing system through the interstellar medium prior to the supernova. We present results of hydrodynamical and spectral modeling aimed at constraining the circumstellar environment of the system and the amount of 56Ni produced in the explosion. Using models that contain either 0.3 M_sun (subenergetic) or 1 M_sun (energetic) of 56Ni, we simulate the interaction between supernova Ia ejecta and various circumstellar density models. Based on dynamical considerations alone, we find that the subenergetic models favor a distance to the SNR of < 6.4 kpc, while the model that produces 1 M_sun of 56Ni requires a distance to the SNR of > 7 kpc. The X-ray spectrum is consistent with an explosion that produced ~ 1 M_sun of 56Ni, ruling out the subenergetic models, and suggesting that Kepler's SNR was a SN 1991T-like event. Additionally, the X-ray spectrum rules out a pure 1/r^2 wind profile expected from isotropic mass loss up to the time of the supernova. Introducing a small cavity around the progenitor system results in modeled X-ray spectra that are consistent with the observed spectrum. If a wind shaped circumstellar environment is necessary to explain the dynamics and X-ray emission from the shocked ejecta in Kepler's SNR, then we require that the distance to the remnant be greater than 7 kpc.

Dust-to-gas ratios in the Kepler supernova remnant

A new method to evaluate the dust-to-gas ratios in the Kepler SNR is presented. Dust emission in the infrared and bremsstrahlung are calculated consistently, considering that dust grains are collisionally heated by the gas throughout the front and downstream of both the expanding and the reverse shocks. The calculated continuum SED is constrained by the observational data. The dust-to-gas ratios are determined by the ratio of the dust emission bump and bremsstrahlung in the infrared. The shell-like morphological similarity of X-ray and radio emission, and of images in Hα and in infrared wavelengths confirms that both radio and X-ray emissions are created at the front of the expanding shock and that dust and gas are coupled crossing the expanding and reverse shock fronts. The results show that large grains with radius of ~1 μm with dust-to-gas ratios <4 10-3 survive sputtering and are heated to a maximum temperature of 125 K downstream of the shock expanding outwards with a velocity of about 1000 . The high velocity shocks become radiative for dust-to-gas ratios >10-3. Such shocks do not appear in the NE region, indicating that dust grains are not homogeneously distributed throughout the remnant. Smaller grains with radius of about 0.2 μm and dust-to-gas ratios of ~4 10-4 are heated to a maximum temperature of ~50 K downstream of the reverse shock corresponding to velocities of about 50 . A maximum dust mass <0.16 is calculated.

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.

H 2–12, a Misidentified Planetary Nebula in Kepler's SNR

H 2–12 (PN 004.5+06.8) is classified as a true or probable planetary nebula (Acker et al. 1992). We obtained narrow-band imagery and long-slit echelle spectra from several positions across H 2–12. It is shown that H 2–12 is associated with one of the brightest condensations located at the periphery of Kepler's SNR. Thus, H 2–12 should be noted as a misclassified PN.

Thermal emission from SNRs and plasma diagnostics

We present here the observational results of Galactic SNRs focusing on their thin thermal emission. Their X-ray spectra give us a good diagnostics of the plasma. Generally, they cannot be fitted by using model spectra in collisional ionization equilibrium (CIE) condition. Some of them show gradients both in the temperature and in the abundance. The X-ray spectrum of young SNRs, like the Kepler's SNR, can be well fitted by the superposition of the fore shock component and the reverse shock component, both of which show gradients in various parameters: temperature, density, ionization parameter etc. Cassiopeia-A, one of the typical young SNR, shows not point symmetric but axial symmetric both in the intensity profile and in the line center energy profile. This suggests the Doppler motion of the plasma about several thousands km/sec. The Cygnus Loop, a middle-aged SNR, also showed gradients: the shell regions show low metal abundance and low temperature while the core region shows high metal abundance and high temperature. The plasma left in the core region must reflect the fossil of the supernova explosion. Based on the metal abundance, we conclude that the Cygnus Loop originated from the type II SN. The Rosat observation on the Vela SNR, another typical middle-aged SNR, revealed that there were several debris running over the shell which was formed by the strong shock propagated in the surrounding medium. ASCA confirmed the abundance anomaly suggesting that they were the fossil of the progenitor star. The plasma both in the young and in the middle-aged SNRs are in the mixing phase of the ejecta with the interstellar matter (ISM).

The Extraordinarily Rapid Expansion of the X‐Ray Remnant of Kepler’s Supernova (SN 1604)

Four individual high resolution X-ray images from ROSAT and the Einstein Observatory have been used to measure the expansion rate of the remnant of Kepler's supernova (SN 1604). Highly significant measurements of the expansion have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All measurements are consistent with a current expansion rate averaged over the entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when combined with the known age of the remnant, determines the expansion parameter m, defined as $R\propto t^m$, to be 0.93 (+/-0.06) (+0.07,-0.04). The error bars on these results include both statistical (first set of errors) and systematic (second set) uncertainty. According to this result the X-ray remnant is expanding at a rate that is remarkably close to free expansion and nearly twice as fast as the mean expansion rate of the radio remnant. The expansion rates as a function of radius and azimuthal angle are also presented based on two ROSAT images that were registered to an accuracy better than 0.5 arcseconds. Significant radial and azimuthal variations that appear to arise from the motion of individual X-ray knots are seen. The high expansion rate of the X-ray remnant appears to be inconsistent with currently accepted dynamical models for the evolution of Kepler's SNR.

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.

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.

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.

EXOSAT observations of the Kepler supernova remnant

view Abstract Citations (16) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS EXOSAT Observations of the Kepler Supernova Remnant Smith, A. ; Peacock, A. ; Arnaud, M. ; Ballet, J. ; Rothenflug, R. ; Rocchia, R. Abstract The medium-energy experiment on board Exosat was used to measure the X-ray spectrum of the Kepler supernova remnant over the range 1.5-10 keV. An Fe emission line was clearly resolved with an energy of about 6.5 keV and equivalent width of about 1.8 keV. This was superposed on a continuum with a temperature of 5.0(+3.8, -1.9) keV. The medium-energy spectrum is shown to be consistent with a model in which the Kepler SNR is presently in a Sedov phase of evolution, the 5 keV continuum arises from the shocked interstellar/circumstellar medium, and thermal (but not ionization) equilibrium exists between electrons and ions behind the primary shock front. However, in this case, an overabundance of iron by more than 6 times cosmic is required. Publication: The Astrophysical Journal Pub Date: December 1989 DOI: 10.1086/168184 Bibcode: 1989ApJ...347..925S Keywords: Exosat Satellite; Stellar Spectra; Supernova Remnants; Supernovae; X Ray Spectra; Interstellar Extinction; Iron; Limb Brightening; Stellar Evolution; Astrophysics; NEBULAE: SUPERNOVA REMNANTS; X-RAYS: SOURCES; X-RAYS: SPECTRA full text sources ADS | data products SIMBAD (1)

S III] 9069, 9532 EMISSION IN ACTIVE GALACTIC NUCLEI

ABSTRACT Observations of the [S III] λλ9069,9532 emission lines in the nuclear spectra of two Seyfert 2 galaxies, four LINERs, and two galaxies, with H II region nuclei are presented. These data are combined with published measurements to reexamine the suggestion by Diaz and collaborators that the relative strengths of the [S II] λλ6716,6731 and [S III] λ λ9069,9532 lines in LINER nuclei provide a powerful method of distinguishing between photoionization and shock heating mechanisms. On the basis of this larger sample of objects, we find general support for the idea that many LINERs are photoionized and form a continuous sequence with Seyfert nuclei characterized by decreasing ionization parameter. Nevertheless, comparison with shock model calculations and published observations of the Kepler SNR shows that the [S II] and [S III] lines alone cannot be used to unambiguously rule out shock models as an alternate explanation for the emission-line spectra of typical LINERs. Indeed, in the case of the LINER nucleus of the luminous infrared galaxy NGC 6240, the observed strengths of these lines would appear to strongly favor shock heating as the dominant source of ionization. Thus, we conclude that both photoionization and shock heating are likely to play significant roles in any given LINER, with either process capable of dominating the observed emission-line spectrum.

The origin of Kepler's supernova remnant

A bow shock model for Kepler's SNR is presented and the motion of the progenitor star with respect to the interstellar medium is examined. The runaway nature of the progenitor is discussed as well as similarities with known runaway objects. It is maintained that binary Wolf-Rayet stars, P Cygni stars, and some binary pulsars could belong to the same evolutionary track leading to Keppler's SNR. 52 references.

A catalog of the H-alpha + N II forbidden-line emission features in the Kepler SNR

A deep image of the Kepler SNR has been obtained in the light of H-alpha + N II forbidden-line with the faint object spectrograph and camera (EFOSC) and a CCD detector at the ESO 3.6 m telescope. The visibility of the optically emitting knots of ionized gas has been greatly enhanced by subtraction of the continuum radiation. Features as faint as 2 percent of the night-sky brightness have been identified and a half-shell of emission is clearly revealed. The total H-alpha luminosity of the ionized gas is estimated to be 8.3 x 10 to the 45th photons/s at a distance of 5 kpc implying a mass of ionized hydrogen of about 0.02 solar mass. An automatic searching program has been used to identify and list individual emission features in the continuum-subtracted image. A catalog with accurate celestial positions and approximate fluxes for 64 emission-line knots is given. 13 references.

Self-consistent models for the X-ray emission from supernova remnants - an application to Kepler's remnant

A tool for exploring the evolution of X-ray emission from young SNRs is presented which employs a novel approach to the problem of time-dependent ionization in a shock-heated plasma. The solution of this problem is coupled to a spherically symmetric hydrodynamic calculation for the evolution of a point explosion in a uniform medium. The method is applied to Kepler's SNR, and two narrowly constrained classes of models which can simultaneously fit the spectral and morphological features of the object are found. One of these is a Sedov model in which the emission arises from shocked ambient gas, and the other is a reverse-shock model in which the SN ejecta is the dominant source of radiation. The emission from one specific model in each class is compared with the radial surface brightness profile, the 0.2-4.5 keV broadband spectrum, and the 1-3 keV moderate-resolution spectrum of the remnant. Reasonable fits are obtained in both cases.

A detailed X-ray and radio comparison of Kepler's supernova remnant

High-resolution radio images of Kepler's SNR (SNR (SN 1604) at 6 and 21 cm have been obtained using the VLA. The orientation of linear polarization in the SNR implies a substantial nonrandom radial component for the magnetic field of the remnant. Based on a new X-ray picture of the SNR, obtained using the Einstein Observatory, a detailed comparison of the X-ray and radio morphology is carried out. There is a good correlation between rotation measure, obtained from the radio maps, and emission measure, an X-ray-derived quantity in the SNR shell. From the mean electron density value infered from an analysis of X-ray fluxes, a mean radial magnetic field of 14 micro G and a total magnetic field of 70 microG are estimated. The energy density of relativistic electrons in Kepler's SNR in the shell comparable to the energy density in the magnetic field; the relativistic electron-pressure is 2 percent of the thermal gas pressure. The strong correlation between radio emissivity and X-ray emissivity found over the SNR in somewhat large scale can be ascribed to acceleration of thermal electrons at the shock wave and insignificant diffusion of resultant relativistic electrons.

High Resolution X-ray Spectra of Supernova Remnants

We review results obtained with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory. Clear evidence is found for departures from ionization equilibrium in the interior of Puppis A. This comes from the observed weakness of the forbidden lines relative to the resonance lines for the He - like triplets of O VII and Ne IX. However, it is shown that this departure from equilibrium does not alter our conclusion, based on previous FPCS results, that O and Ne are overabundant relative to Fe. The spectrum of N132D shows strong O VIII emission and very weak Fe emission, suggesting an even greater O/Fe abundance enhancement than in Puppis A. In the Cygnus Loop, the O to Ne abundance ratio is approximately solar; we have no information about Fe. The O VII triplet shows clear evidence for departures from ionization equilibrium in the Cygnus Loop. The spectrum of Tycho's SNR contains lines from ionization stages of Fe XVII through Fe XXIII and XXIV, indicating that a wide range of ionization conditions are present. Cas A and Kepler's SNR show relatively less emission from the higher ionization stages. For Tycho, we measured the strength of the strong Si XIII lines, and we find that a many-fold overabundance of Si relative to Fe is required regardless of the equilibrium state of the emitting plasma (confirming the Solid State Spectrometer results). On a separate topic, the completed analysis of X-ray Doppler shifts in Cas A suggests that the emitting material is concentrated in a ring that is inclined to the line of sight and is expanding at ~5000 km s−1.

The X-ray surface brightness of Kepler's supernova remnant

The first X-ray images of Kepler's supernova remnant (SN Ophiuchi 1604) are presented, and consequences for SNR models are discussed. Observations made with the Einstein Observatory Imaging Proportional Counter and High Resolution Imager show the remnant to be circular, with a strong shell brighter in the north than in the south. A flux of 1.2 x 10 to the -10th ergs/sq cm per sec was measured in the 0.15-4.5 keV region, which corresponds to an X-ray luminosity of 1.0 x 10 to the 36th ergs/sec at a distance of 5 kpc and an interstellar medium density of 2.8 x 10 to the 21st/sq cm. The X-ray observations do not allow the determination of whether the SNR is in the adiabatic or free expansion phase, but in either case it is shown that the mean ISM density must be greater than about 0.1/cu cm. In addition, the density of the X-ray emitting gas must be high, and its electron temperature must be fairly low. The high ISM densities derived for Kepler's SNR and other SNRs thus suggest an atypical ISM, possibly influenced by mass lost from the pre-supernova star.