DEM L71 Research Articles

Spatially Resolved Chandra Spectroscopy of Supernova Remnant DEM L71 in the Large Magellanic Cloud

ABSTRACT We present a detailed X-ray spectroscopic study of the supernova remnant (SNR) DEM L71 in the Large Magellanic Cloud. Based on deep ∼103 ks archival Chandra data, we perform a detailed spatially resolved spectral analysis of DEM L71. We analyse regional spectra extracted from thin-sliced regions along several different azimuthal directions of the SNR to construct radial profiles of elemental abundances for O, Ne, Mg, Si, and Fe. Our elemental abundance measurements reveal an asymmetrical spatial distribution of metal-rich ejecta gas. Especially the asymmetry in the western part of the central Fe distribution is remarkable. While the location of the contact discontinuity is generally at ∼5 pc from the geometric center of the X-ray emission of DEM L71, it is uncertain in the western part of the remnant. Fe is enhanced in the ejecta while O and Ne abundances are generally negligible. This finding confirms the Type Ia origin of DEM L71. We estimate an upper limit on the Sedov age of ∼6660 ± 770 yr and explosion energy of ∼1.74 ± 0.35 × 1051 erg for the remnant. This explosion energy estimate is consistent with a canonical explosion of a type Ia SNR.

Forbidden Line Emission from Type Ia Supernova Remnants Containing Balmer-dominated Shells

Abstract Balmer-dominated shells in supernova remnants (SNRs) are produced by collisionless shocks advancing into a partially neutral medium and are most frequently associated with Type Ia supernovae. We have analyzed Hubble Space Telescope (HST) images and Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) or AAT/Wide Field Integral Spectrograph observations of five Type Ia SNRs containing Balmer-dominated shells in the LMC: 0509–67.5, 0519–69.0, N103B, DEM L71, and 0548–70.4. Contrary to expectations, we find bright forbidden-line emission from small dense knots embedded in four of these SNRs. The electron densities in some knots are higher than 104 cm−3. The size and density of these knots are not characteristic for interstellar medium—they most likely originate from a circumstellar medium ejected by the SN progenitor. Physical property variations of dense knots in the SNRs appear to reflect an evolutionary effect. The recombination timescales for high densities are short, and HST images of N103B taken 3.5 yr apart already show brightness changes in some knots. VLT/MUSE observations detect [Fe xiv] line emission from reverse shocks into SN ejecta as well as forward shocks into the dense knots. Faint [O iii] line emission is also detected from the Balmer shell in 0519–69.0, N103B, and DEM L71. We exclude the postshock origin because the [O iii] line is narrow. For the preshock origin, we considered three possibilities: photoionization precursor, cosmic-ray precursor, and neutral precursor. We conclude that the [O iii] emission arises from oxygen that has been photoionized by [He ii] λ304 photons and is then collisionally excited in a shock precursor heated mainly by cosmic rays.

Can the Fe K-alpha Line Reliably Predict Supernova Remnant Progenitors?

Abstract The centroid energy of the Fe Kα line has been used to identify the progenitors of supernova remnants (SNRs). These investigations generally considered the energy of the centroid derived from the spectrum of the entire remnant. Here we use XMM-Newton data to investigate the Fe Kα centroid in 6 SNRs: 3C 397, N132D, W49B, DEM L71, 1E 0102.2-7219, and Kes 73. In Kes 73 and 1E 0102.2-7219, we fail to detect any Fe Kα emission. We report a tentative first detection of Fe Kα emission in SNR DEM L71 with a centroid energy consistent with its Type Ia designation. In the remaining remnants, the spatial and spectral sensitivity is sufficient to investigate spatial variations of the Fe Kα centroid. We find in N132D and W49B that the centroids in different regions are consistent with those derived from the overall spectrum, although not necessarily with the remnant type identified via other means. However, in SNR 3C 397, we find statistically significant variation in the centroid of up to 100 eV, aligning with the variation in the density structure around the remnant. These variations span the intermediate space between centroid energies signifying core-collapse (CC) and Type Ia remnants. Shifting the dividing line downwards by 50 eV can place all the centroids in the CC region, but contradicts the remnant type obtained via other means. Our results show that caution must be used when employing the Fe Kα centroid of the entire remnant as the sole diagnostic for typing a remnant.

Smoothed particle inference analysis and abundance calculations of DEM L71, and comparison to SN explosion models

AbstractWe analyze the X‐ray emission from the supernova remnant DEM L71 using the smoothed particle inference (SPI) technique. The high Fe abundance found appears to confirm the Type Ia origin. Our method allows the separation of the material ejected in the supernova explosion from the material swept up by the supernova shock wave. We are able to calculate the total mass of this swept‐up material to be about 228 ± 23 M⊙. We plot the posterior distribution for the number density parameter, and create a map of the density structure within the remnant. While the observed density shows substantial variations, we find our results are generally consistent with a two‐dimensional hydrodynamical model of the remnant that we have run. Assuming the ejected material arises from a Type Ia explosion, with no hydrogen present, we use the predicted yields from Type Ia models available in the literature to characterize the emitting gas. We find that the abundance of various elements match those predicted by deflagration‐to‐detonation transition (DDT) models. Our results, compatible with the Type Ia scenario, highlight the complexity of the remnant and the nature of the surrounding medium.

Search for Surviving Companions of Progenitors of Young LMC SN Ia Remnants

Abstract We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants in the Large Magellanic Cloud: 0519–69.0, 0505–67.9 (DEM L71), and 0548–70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color–magnitude diagrams (CMDs) and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main-sequence or helium star companions. No obvious candidates of surviving companions are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi Unit Spectroscopic Explorer observations of 0519–69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519–69.0 and a star in DEM L71 moving at radial velocities of 182 ± 0 km s−1 and 213 ± 0 km s−1, respectively, more than 2.5σ from the mean radial velocity of the underlying stellar population, 264 and 270 km s−1, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the supernova progenitors.

Smoothed Particle Inference Analysis of SNR DEM L71

Supernova remnants (SNRs) are complex, three-dimensional objects; properly accounting for this complexity when modeling the resulting X-ray emission presents quite a challenge and makes it difficult to accurately characterize the properties of the full SNR volume. We apply for the first time a novel analysis method, Smoothed Particle Inference, that can be used to study and characterize the structure, dynamics, morphology, and abundances of the entire remnant with a single analysis. We apply the method to the Type Ia supernova remnant DEM L71. We present histograms and maps showing global properties of the remnant, including temperature, abundances of various elements, abundance ratios, and ionization age. Our analysis confirms the high abundance of Fe within the ejecta of the supernova, which has led to it being typed as a Ia. We demonstrate that the results obtained via this method are consistent with results derived from numerical simulations carried out by us, as well as with previous analyses in the literature. At the same time, we show that despite its regular appearance, the temperature and other parameter maps exhibit highly irregular substructure which is not captured with typical X-ray analysis methods.

Balmer-dominated Shocks Exclude Hot Progenitors for Many Type Ia Supernovae

Abstract The evolutionary mechanism underlying Type Ia supernova explosions remains unknown. However, recent efforts to constrain progenitor models based on the influence that their high energy emission would have on the interstellar medium within galaxies have proven successful. For individual remnants, Balmer-dominated shocks reveal the ionization state of hydrogen in the immediately surrounding gas. Here, we report deep upper limits on the temperature and luminosity of the progenitors of four Type Ia remnants with associated Balmer filaments: SN 1006, 0509-67.5, 0519-69.0, and DEM L71. For SN 1006, existing observations of helium-line emission in the diffuse emission ahead of the shock provide an additional constraint on the helium ionization state in the vicinity of the remnant. Using the photoionization code Cloudy, we show that these constraints exclude any hot, luminous progenitor for SN 1006, including stably hydrogen or helium nuclear-burning white dwarfs (WD), as well as any Chandrasekhar-mass WD accreting matter at ≳9.5 × 10−8 M ⊙ yr−1 via a disk. For 0509-67.5, the Balmer emission alone rules out any such WD accreting ≳1.4 × 10−8 M ⊙ yr−1. For 0519-69.0 and DEM L71, the inferred ambient ionization state of hydrogen is only weakly in tension with a recently hot, luminous progenitor, and cannot be distinguished from, e.g., a relatively higher local Lyman continuum background, without additional line measurements. Future deep spectroscopic observations will resolve this ambiguity, and can either detect the influence of any luminous progenitor or rule out the same for all resolved SN Ia remnants.

A CHANDRA STUDY OF THE INTERSTELLAR METALLICITY IN THE LARGE MAGELLANIC CLOUD USING SUPERNOVA REMNANTS

ABSTRACT We report on the results from our measurements of the interstellar medium (ISM) abundances for the elements O, Ne, Mg, Si, and Fe in the Large Magellanic Cloud (LMC). We used the archival Chandra data for sixteen supernova remnants (SNRs) in the LMC (0453-68.5, DEM L71, N23, 0519-69.0, N49B, N132D, N49, N206, 0534-69.9, DEM L238, N63A, Honeycomb, N157B, 0540-69.3, DEM L316B, and 0548-70.4). Our results represent LMC abundance measurements based on the modern Chandra data. We place tight constraints on our measured elemental abundances and find lower abundances than previous measurements by Hughes et al. (by a factor of approximately two on average except for Si) who utilized similar methods based on a smaller sample of ASCA data of SNRs in the LMC. We discuss the origins of the discrepancy between our Chandra and the previous ASCA measurements. We also discuss our results in comparison with the LMC abundance measurements in the literature.

N49: THE FIRST ROBUST DISCOVERY OF RECOMBINING PLASMA IN AN EXTRA GALACTIC SUPERNOVA REMNANT

Recent discoveries of recombining plasmas (RPs) in supernova remnants (SNRs) have dramatically changed our understanding of SNR evolution. To date, a dozen of RP SNRs have been identified in the Galaxy. Here we present Suzaku deep observations of four SNRs in the Large Magellanic Cloud (LMC), N49, N49B, N23, and DEM L71, for accurate determination of their plasma state. Our uniform analysis reveals that only N49 is in the recombining state among them, which is the first robust discovery of a RP from an extra-galactic SNR. Given that RPs have been identified only in core-collapse SNRs, our result strongly suggests a massive star origin of this SNR. On the other hand, no clear evidence for a RP is confirmed in N23, from which detection of recombination lines and continua was previously claimed. Comparing the physical properties of the RP SNRs identified so far, we find that all of them are categorized into the "mixed-morphology" class and interacting with surrounding molecular clouds. This might be a key to solve formation mechanisms of the RPs.

THE STELLAR ANCESTRY OF SUPERNOVAE IN THE MAGELLANIC CLOUDS. I. THE MOST RECENT SUPERNOVAE IN THE LARGE MAGELLANIC CLOUD

We use the star formation history map of the Large Magellanic Cloud recently published by Harris & Zaritsky to study the sites of the eight smallest (and presumably youngest) supernova remnants in the Cloud: SN 1987A, N158A, N49, and N63A (core collapse remnants), 0509 67.5, 0519 69.0, N103B, and DEM L71 (Type Ia remnants). The local star formation histories provide unique insights into the nature of the supernova progenitors, which we compare with the properties of the supernova explosions derived from the remnants themselves and from supernova light echoes. We find that all the core collapse supernovae that we have studied are associated with vigorous star formation in the recent past. In the case of SN 1987A, the time of the last peak of star formation (12 Myr) matches the lifetime of a star with the known mass of its blue supergiant progenitor (� 20M⊙). More recent peaks of star formation can lead to supernovae with more massive progenitors, which opens the possibility of a Type Ib/c origin for SNRs N158A and N63A. Stars more massive than 21.5M⊙ are very scarce around SNR N49, implying that the magnetar SGR 0526 66 in this SNR was either formed elsewhere or came from a progenitor with a mass well below the 30M⊙ threshold suggested in the literature. Three of our four Ia SNRs are associated with old, metal poor stellar populations. This includes SNR 0509 67.5, which is known to have been originated by an extremely bright Type Ia event, and yet is located very far away from any sites of recent star formation, in a population with a mean age of 7.9 Gyr. The Type Ia SNR N103B, on the other hand, is associated with recent star formation, and might have had a relatively younger and more massive progenitor with substantial mass loss before the explosion. We discuss these results in the context of our present understanding of core collapse and Type Ia supernova progenitors.

THE Hα DIAGNOSTIC OF ELECTRON HEATING: THE CASE OF DEM L71

Recently, the mechanisms and extent of immediate postshock heating of electrons at collisionless shocks have been under intense investigation. Several recent studies have suggested that the ratio of electron to proton temperature at the shock front scales approximately as the inverse square of the shock velocity. A specific interpretation of this dependence was first introduced by Ghavamian et al., who suggested electron heating by lower-hybrid waves in a cosmic ray (CR) precursor as a possible mechanism behind such a relationship. The best line diagnostics for the electron to proton temperature ratio behind collisionless shocks in partially neutral gas are the combination of broad and narrow H{alpha} lines emitted in the immediate vicinity of the shock front. In this work, we present extensive long-slit spectroscopy of the H{alpha} emission in the blast wave shock of supernova remnant DEM L71. We chose this remnant for two main reasons. First, the shock velocities in DEM L71 span the range of speeds where the electron to proton temperature ratio varies most rapidly with shock speed. Second, previous Fabry-Perot scans of the H{alpha} line complex indicated broad-to-narrow flux ratios lower than existing models predicted, but the spectral coverage of those observations was not broad enoughmore » to reliably measure the background emission around the broad component H{alpha} line. Our new high-resolution (R {approx}> 1600) spectra of DEM L71 provide extensive coverage of the background near the H{alpha} line and confirm our earlier Fabry-Perot results of consistently low ({approx}<1) broad-to-narrow flux ratios. Here, we present results of these observations and also outline the first results from spectra of radiative portions of DEM L71. We compare our results to the latest models of H{alpha} profiles from collisionless shocks. We conclude that the most likely explanation for the low broad-to-narrow flux ratio is the ionization and excitation of neutrals by electrons heated in the extended CR precursor.« less

Dust Destruction in Type Ia Supernova Remnants in the Large Magellanic Cloud

We present first results from an extensive survey of Magellanic Cloud supernova remnants (SNRs) with the Spitzer Space Telescope. We describe IRAC and MIPS imaging observations at 3.6, 4.5, 5.8, 8, 24, and 70 μm of four Balmer-dominated Type Ia SNRs in the Large Magellanic Cloud (LMC): DEM L71 (0505-67.9), 0509-67.5, 0519-69.0, and 0548-70.4. None was detected in the four short-wavelength IRAC bands, but all four were clearly imaged at 24 μm, and two at 70 μm. A comparison of these images with Chandra broadband X-ray images shows a clear association with the blast wave, and not with internal X-ray emission associated with ejecta. Our observations are well described by one-dimensional shock models of collisionally heated dust emission, including grain size distributions appropriate for the LMC, grain heating by collisions with both ions and electrons, and sputtering of small grains. Model parameters are constrained by X-ray, optical, and far-ultraviolet observations. Our models can reproduce observed 70/24 μm flux ratios only by including sputtering, destroying most grains smaller than 0.03-0.04 μm in radius. We infer total dust masses swept up by the SNR blast waves, before sputtering, on the order of 10-2 M☉, several times less than those implied by a dust-to-gas mass ratio of 0.3% as often assumed for the LMC. Substantial dust destruction has implications for gas-phase abundances.

The Physics of Supernova Blast Waves. I. Kinematics of DEM L71 in the Large Magellanic Cloud

We present the results from Fabry-Perot imaging spectroscopy of the Balmer-dominated supernova remnant DEM L71 (0505-67.9) in the LMC. Spectra extracted from the entire circumference of the blast wave reveal the broad- and narrow-component Hα line emission characteristic of nonradiative shocks in partially neutral gas. The new spectra of DEM L71 include portions of the rim that have not been previously observed. We find that the broad-component width varies azimuthally along the edge of DEM L71, ranging from 450 ± 60 km s-1 along the eastern edge to values as high as 985 km s-1 along the faint western edge. The latter width is nearly 60% larger than the value determined by earlier spectroscopy of the brightest Balmer-dominated filaments. In part of the faint northern rim the broad component is not detected, possibly indicating a lower density in these regions and/or a broad-component width in excess of 1000 km s-1. Between the limits of zero and full electron-ion temperature equilibration at the shock front, the allowed range of shock velocities is 430-560 km s-1 along the east rim and 700-1250 km s-1 along other parts of the blast wave. The Hα broad-to-narrow flux ratios vary considerably around the remnant, ranging from 0.4 to 0.8. These ratios lie below the values predicted by our shock models. We find that narrow-component Hα emission from a cosmic-ray precursor may be the cause of the discrepancy. The least decelerated portions of the blast wave (i.e., regions excluding the brightest filaments) are well characterized by Sedov models with a kinetic energy E51 = (0.37 ± 0.06)D, where D50 is the LMC distance in units of 50 kpc. The corresponding age for DEM L71 is (4360 ± 290)D50 yr. This is the first time that velocity information from the entire blast wave has been utilized to study the global kinematics of a nonradiative supernova remnants at a known distance.

The Physics of Supernova Remnant Blast Waves. II. Electron‐Ion Equilibration in DEM L71 in the Large Magellanic Cloud

We present analysis and modeling of X-ray spectra from the blast wave shock of DEM L71 in the Large Magellanic Cloud. This remnant exhibits widespread Balmer-dominated emission characteristic of nonradiative shocks in partially neutral gas. We have used Chandra ACIS-S data and optical Fabry-Perot spectra of the blast wave to measure the electron and proton temperatures, respectively. In principle, when combined, these measurements can determine the degree of electron-ion temperature equilibration (g0 ≡ Te/Tp) immediately behind the shock front. In our X-ray analysis we fit Chandra spectra of three nested regions behind the blast wave under three different scenarios: (1) a planar, initially unequilibrated shock (g0 = me/mp), where the downstream electron and proton temperatures equilibrate through Coulomb collisions, (2) a planar, immediately equilibrated shock (g0 = 1), and (3) a spherical, equilibrated shock under Sedov evolution. Using independent measurements of Te and Tp, we find that the X-ray spectra from the fastest blast wave locations (Vs ~ 700-1000 km s-1) are consistent with little or no equilibration at the shock front and are inconsistent with full equilibration. In contrast, spectra from regions showing slower blast wave speeds (Vs ~ 400-600 km s-1) allow full equilibration but exclude zero equilibration. In order to directly constrain the initial equilibration, we incorporated our knowledge of the proton temperatures into our X-ray models to build planar shock models that allow for a variable g0. This model confirmed and strengthened the above results. Specifically, we found that X-ray spectra from an intermediate-velocity shock (Vs ~ 800 km s-1) were consistent with intermediate equilibration, excluding both g0 = me/mp and g0 = 1 at greater than 1 σ. Overall, our results support the picture of decreasing electron-ion equilibration with increasing shock speed found from previous studies of optical spectra in other Balmer-dominated supernova remnants.

Iron-rich Ejecta in the Supernova Remnant DEM L71

Chandra X-ray observations of DEM L71, a supernova remnant (SNR) in the Large Magellanic Cloud (LMC), reveal a clear double shock morphology consisting of an outer blast wave shock surrounding a central bright region of reverse-shock heated ejecta. The abundances of the outer shock are consistent with LMC values, while the ejecta region shows enhanced abundances of Si, Fe, and other species. However, oxygen is not enhanced in the ejecta; the Fe/O abundance ratio there is more than 5 times the solar ratio. Based on the relative positions of the blast wave shock and the contact discontinuity in the context of SNR evolutionary models, we determine a total ejecta mass of approximately 1.5 solar masses. Ejecta mass estimates based on emission measures derived from spectral fits are subject to considerable uncertainty due to lack of knowledge of the true contribution of hydrogen continuum emission. Maximal mass estimates, i.e., assuming no hydrogen, result in 1.5 solar masses of Fe and 0.24 solar masses of Si. Under the assumption that an equal quantity of hydrogen has been mixed into the ejecta, we estimate 0.8 solar masses of Fe and 0.12 solar masses of Si. These characteristics support the view that in DEM L71 we see Fe-rich ejecta from a Type Ia SN several thousand years after explosion.