Large Magellanic Cloud Supernova Remnants Research Articles

New radio continuum study of the large magellanic cloud supernova remnant N49

Abstract We present new Australia Telescope Compact Array (ATCA) radio observations towards N 49, one of the brightest extragalactic supernova remnants (SNRs) located in the Large Magellanic Cloud (LMC). Our new and archival ATCA radio observations were analysed along with Chandra X-ray data. These observations show a prominent ‘bullet’ shaped feature beyond the southwestern boundary of the SNR. Both X-ray morphology and radio polarisation analysis support a physical connection of this feature to the SNR. The ‘bullet’ feature’s apparent velocity is estimated at $\sim$ 1 300 km s $^{-1}$ , based on its distance ( $\sim$ 10 pc) from the remnant’s geometric centre and estimated age ( $\sim$ 7 600 yr). we estimated the radio spectral index, $\alpha= -0.55 \pm 0.03$ which is typical of middle-age SNRs. Polarisation maps created for N 49 show low to moderate levels of mean fractional polarisation estimated at 7 $\pm$ 1% and 10 $\pm$ 1% for 5.5 and 9 GHz, respectively. These values are noticeably larger than found in previous studies. Moreover, the mean value for the Faraday rotation of SNR N 49 from combining CABB data is 212 $\pm$ 65 rad m $^{-2}$ and the maximum value of RM is 591 $\pm$ 103 rad m $^{-2}$ .

Radio continuum study of the Large Magellanic Cloud supernova remnant Honeycomb Nebula

We present the first and deepest Australia Telescope Compact Array radio continuum images of the Honeycomb Nebula at 2000 and 5500MHz solely from archival data. The resolutions of these images are 3:6 x 2:8 arcsec2 and 1:3 x 1:2 arcsec2 at 2000 and 5500 MHz. We find an average radio spectral index for the remnant of -0:76?0:07. Polarisation maps at 5500MHz reveal an average fractional polarisation of 25 ? 5% with a maximum value of 95 ? 16. We estimate the equipartition field for Honeycomb Nebula of 48 ? 5 ?G, with an estimated minimum energy of Emin = 3 x 1049 erg. The estimated surface brightness, ?1 GHz, is 30 x 10-20Wm-2 Hz-1 sr-1; applying the ?-D relation suggests this supernova remnant is expanding into a low-density environment. Finally, using Hi data, we can support the idea that the Honeycomb Nebula exploded inside a low-density wind cavity. We suggest that this remnant is likely to be between late free expansion stage and early Sedov phase of evolution and expanding into a low-density medium.

The Large Magellanic Cloud Supernova Remnant MCSNR J0550-6823

We describe radio, optical, and X-ray observations of this rather faint, old Large Magellanic Cloud (LMC) supernova remnant. The [O iii] emission forms a distinct shell, the remnant of the outer shock, which encloses the radio and X-ray emission and gives an estimate of age and explosion energy. Because of a collision with an LMC Hα filament, radio and X-ray emission are concentrated in the northern half of the remnant. The X-ray spectrum is well fit assuming the plasma is isothermal and in collisional equilibrium. The best-fit temperature is such that almost all energy is in lines from O, Ne, Mg, and Fe. The known distance, low extinction, and low interstellarmedium metallicity allow derivation of masses of several elements produced by the star and in the explosion. The masses of O, Ne, and Fe point to a Type II supernova from the explosion of a 20–25 M ⊙ star. The mass of Mg, however, is higher than that of almost all predictions, but some of this apparent excess might be due to a higher-temperature region in the X-ray-emitting material. Point-like background sources are examined to search for a neutron star, and one possible candidate is found just inside the shell of the remnant.

An X-Ray Proper-motion Study of the Large Magellanic Cloud Supernova Remnant 0509-67.5

We present a third epoch of Chandra observations of the Type Ia Large Magellanic Cloud Supernova remnant 0509-67.5. With these new observations from 2020, the baseline for proper-motion measurements of the expansion has grown to 20 yr (from the earliest Chandra observations in 2000). We report here the results of these new expansion measurements. The lack of nearby bright point sources renders absolute image alignment difficult. However, we are able to measure the average expansion of the diameter of the remnant along several projection directions. We find that the remnant is expanding with an average velocity of 6120 (4900–7360) km s−1. This high shock velocity is consistent with previous works, and also consistent with the inference that 0509-67.5 is expanding into a very low density surrounding medium. At the distance of the LMC, this velocity corresponds to an undecelerated age of 600 yr, with the real age somewhat smaller.

New ASKAP radio supernova remnants and candidates in the Large Magellanic Cloud

ABSTRACT We present a new Australian Square Kilometre Array Pathfinder (ASKAP) sample of 14 radio supernova remnants (SNR) candidates in the Large Magellanic Cloud (LMC). This new sample is a significant increase to the known number of older, larger, and low surface brightness LMC SNRs. We employ a multifrequency search for each object and found possible traces of optical and occasionally X-ray emission in several of these 14 SNR candidates. One of these 14 SNR candidates (MCSNR J0522 – 6543) has multifrequency properties that strongly indicate a bona fide SNR. We also investigate a sample of 20 previously suggested LMC SNR candidates and confirm the SNR nature of MCSNR J0506 – 6815. We detect lower surface brightness SNR candidates which were likely formed by a combination of shock waves and strong stellar winds from massive progenitors (and possibly surrounding OB stars). Some of our new SNR candidates are also found in lower density environments in which SNe type Ia explode inside a previously excavated interstellar medium.

An exploration of X-ray Supernova remnants in the Milky Way and nearby galaxies

ABSTRACT We probe the environmental properties of X-ray supernova remnants (SNRs) at various points along their evolutionary journey, especially the S-T phase, and their conformance with theoretically derived models of SNR evolution. The remnant size is used as a proxy for the age of the remnant. Our data set includes 34 Milky Way, 59 Large Magellanic Cloud (LMC), and 5 Small Magellanic Cloud (SMC) SNRs. We select remnants that have been definitively typed as either core-collapse (CC) or Type Ia supernovae, with well-defined size estimates, and a thermal X-ray flux measured over the entire remnant. A catalog of SNR size and X-ray luminosity is presented and plotted, with ambient density and age estimates from the literature. Model remnants with a given density, in the Sedov-Taylor (S-T) phase, are overplotted on the diameter-versus-luminosity plot, allowing the evolutionary state and physical properties of SNRs to be compared to each other, and to theoretical models. We find that small, young remnants are predominantly Type Ia remnants or high luminosity CCs, suggesting that many CC SNRs are not detected until after they have emerged from the progenitor’s wind-blown bubble. An examination of the distribution of SNR diameters in the Milky Way and LMC reveals that LMC SNRs must be evolving in an ambient medium which is 30 per cent as dense as that in the Milky Way. This is consistent with ambient density estimates for the Galaxy and LMC.

XMM Observation of the Supernova Remnant J0454-6713 and the Adjacent N9 Superbubble

Abstract The Large Magellanic Cloud supernova remnant J0454-6713 abutting the H ii region N9 has been observed with XMM-Newton. Two groups of lines from Fe xvii account for half the emission and lines from Fe xviii, O vii, and O viii are also clearly detected with the XMM RGS. Isothermal equilibrium fits of the EPIC spectra reproduce the basic spectral form and show little variation throughout the remnant but are insensitive to the lines from the high-temperature ions. These are overwhelmed in the EPIC cameras by the dominant Fe xvii radiation and the EPIC best-fit spectra do not agree with the RGS data. Uncertainties in the atomic data used to determine Fe-line strength present a further complication which inhibits a good EPIC spectral fit. We build a two-temperature model which does fit both RGS and EPIC results and propose that the high-T component is from SN debris and the low from heated material in the H ii region. The high ratio of Fe emission to that from O requires the remnant to be the product of a Type Ia supernova and points to a deflagration–detonation origin. Weak X-ray emission from the N9 superbubble is detected and briefly discussed. The abundance of Ne in N9 material seems higher than average for the LMC in both the superbubble spectrum and the low-temperature component of the remnant RGS spectrum.

New optically identified supernova remnants in the Large Magellanic Cloud

ABSTRACT We present a new optical sample of three Supernova Remnants (SNRs) and 16 Supernova Remnant (SNR) candidates in the Large Magellanic Cloud (LMC). These objects were originally selected using deep H α, [S ii], and [O iii] narrow-band imaging. Most of the newly found objects are located in less dense regions, near or around the edges of the LMC’s main body. Together with previously suggested MCSNR J0541–6659, we confirm the SNR nature for two additional new objects: MCSNR J0522–6740 and MCSNR J0542–7104. Spectroscopic follow-up observations for 12 of the LMC objects confirm high [S ii]/H α emission-line ratios ranging from 0.5 to 1.1. We consider the candidate J0509–6402 to be a special example of the remnant of a possible type Ia Supernova (SN) which is situated some 2° (∼1.75 kpc) north from the main body of the LMC. We also find that the SNR candidates in our sample are significantly larger in size than the currently known LMC SNRs by a factor of ∼2. This could potentially imply that we are discovering a previously unknown but predicted, older class of large LMC SNRs that are only visible optically. Finally, we suggest that most of these LMC SNRs are residing in a very rarefied environment towards the end of their evolutionary span where they become less visible to radio and X-ray telescopes.

Spatially Resolved Chandra Spectroscopy of the Large Magellanic Cloud Supernova Remnant N132D

Abstract We perform detailed spectroscopy of the X-ray-brightest supernova remnant in the Large Magellanic Cloud (LMC), N132D, using Chandra archival observations. By analyzing the spectra of the entire well-defined rim, we determine the mean abundances for O, Ne, Mg, Si, S, and Fe for the local LMC environment. We find evidence of enhanced O on the northwestern and S on the northeastern blast wave. By analyzing spectra interior to the remnant, we confirm the presence of a Si-rich, relatively hot plasma (≳1.5 keV) that is also responsible for the Fe K emission. Chandra images show that the Fe K emission is distributed throughout the interior of the southern half of the remnant but does not extend out to the blast wave. We estimate the progenitor mass to be 15 ± 5 M ⊙ using abundance ratios in different regions that collectively cover a large fraction of the remnant, as well as from the radius of the forward shock compared with models of an explosion in a cavity created by stellar winds. We fit ionizing and recombining plasma models to the Fe K emission and find that the current data cannot distinguish between the two, so the origin of the high-temperature plasma remains uncertain. Our analysis is consistent with N132D being the result of a core-collapse supernova in a cavity created by its intermediate-mass progenitor.

Dust Destruction in Nonradiative Shocks

Supernova remnant (SNR) shock waves are the main place where interstellar dust grains are destroyed. However, the dust destruction efficiency in non-radiative shocks is still not well known. One way to estimate the fraction of dust destroyed is to compare the difference between postshock gas abundances and preshock medium total abundances when the preshock elemental depletion factors are known. We compare the postshock gas abundances of 16 SNRs in Large Magellanic Cloud (LMC) with the LMC interstellar medium abundances that we derived based on 69 slow-rotating early B-type stars. We find that, on average, $\sim$61\% of Si rich dust grains are destroyed in the shock while the fraction of dust destroyed is only $\sim$40\% for Fe rich dust grains. This result supports the idea that the high depletion of Fe in the diffuse neutral medium is not caused by the resilience of Fe rich grains but because of faster growth rate. This work also presents a potential way to constrain the chemical composition of interstellar dust.

Evolutionary Models for 15 Galactic Supernova Remnants with New Distances

Abstract Recent studies using 21 cm H i line and 13CO line observations in the inner part of the Galaxy have resulted in new distances for 30 Galactic supernova remnants (SNRs). Of those remnants, 15 have observed X-ray spectra, for which shocked-gas temperatures and emission measures are measured. Here we apply spherically symmetric SNR evolution models to these 15 remnants to obtain estimates for ages, explosion energies, circumstellar medium densities and profiles (uniform or wind-type). From the distribution of ages we obtain a supernova birth rate and estimate incompleteness. The energies and densities can be well fit with log-normal distributions. The distribution of explosion energies is very similar to that of SNRs in the Large Magellanic Cloud (LMC), suggesting that SN explosions in the LMC and in the Galaxy are very similar. The density distribution has higher mean density for Galactic SNRs than for LMC SNRs by a factor ∼2.5.

The Expansion of the Young Supernova Remnant 0509-68.7 (N103B)

Abstract We present a second epoch of Chandra observations of the Type Ia Large Magellanic Cloud supernova remnant (SNR) 0509-68.7 (N103B) obtained in 2017. When combined with the earlier observations from 1999, we have a 17.4 year baseline with which we can search for evidence of the remnant’s expansion. Although the lack of strong point source detections makes absolute image alignment at the necessary accuracy impossible, we can measure the change in the diameter and the area of the remnant, and find that it has expanded by an average velocity of 4170 (2860, 5450) km s−1. This supports the picture of this being a young remnant; this expansion velocity corresponds to an undecelerated age of 850 years, making the real age somewhat younger, consistent with results from light echo studies. Previous infrared observations have revealed high densities in the western half of the remnant, likely from circumstellar material, so it is probable that the real expansion velocity is lower on that side of the remnant and higher on the eastern side. A similar scenario is seen in Kepler’s SNR. N103B joins the rare class of Magellanic Cloud SNRs with measured proper motions.

X-Ray Luminosity and Size Relationship of Supernova Remnants in the LMC

Abstract The Large Magellanic Cloud (LMC) has ∼60 confirmed supernova remnants (SNRs). Because of the known distance, 50 kpc, the SNRs’ angular sizes can be converted to linear sizes, and their X-ray observations can be used to assess X-ray luminosities (L X). We have critically examined the LMC SNRs’ sizes reported in the literature to determine the most plausible sizes. These sizes and the L X determined from XMM-Newton observations are used to investigate their relationship to explore the environmental and evolutionary effects on the X-ray properties of SNRs. Our research provides the following three results. (1) Small LMC SNRs, a few to 10 pc in size, are all Type Ia with L X > 1036 erg s−1. The scarcity of small core-collapse (CC) SNRs is a result of CC SNe exploding in the low-density interiors of interstellar bubbles blown by their massive progenitors during their main-sequence phase. (2) Medium-sized (10–30 pc) CC SNRs show bifurcation in L X, with the X-ray-bright SNRs either in an environment associated with molecular clouds or containing pulsars and pulsar-wind nebulae and the X-ray-faint SNRs being located in low-density interstellar environments. (3) Large (size > 30 pc) SNRs show a trend of L X fading with size, although the scatter is large. The observed relationship between L X and sizes can help constrain models of SNR evolution.

J0453-6655, the Supernova Remnant in N4D

Abstract The Large Magellanic Cloud supernova remnant J0453-6655 in the H ii region N4 has been observed with XMM-Newton and with Chandra. Almost all of the diffuse X-ray emission is from within a 3.′5 × 2.′3 region of bright optical filaments, and X-ray results from XMM-Newton and Chandra are very similar. Spectra indicate that the plasma is close to equilibrium and that the remnant is likely the result of a Type II supernova powered by the collapse of a <12 M ⊙ star. Composition, density, and mass of the X-ray-emitting plasma are derived, and the age of the remnant is estimated to be 60–80 kyr. There is an apparent blowout of energy into an adjoining cavity. Because cooling neutron stars are objects of interest, the surrounding sky is searched for possible compact remnants of the core. There are six point-like sources within the remnant, all rather faint. Two are probably background active galactic nuclei. The others have soft spectral components and no IR counterparts, but, with the present data, none can be proved to be a neutron star. They do represent upper limits to any neutron star luminosity.

Shocked Interstellar Clouds and Dust Grain Destruction in the LMC Supernova Remnant N132D

Abstract From integral field data we extract the optical spectra of 20 shocked clouds in the supernova remnant N132D in the Large Magellanic Cloud (LMC). Using self-consistent shock modeling, we derive the shock velocity, pre-shock cloud density, and shock ram pressure in these clouds. We show that the [Fe x] and [Fe xiv] emission arises in faster, partially radiative shocks moving through the lower-density gas near the periphery of the clouds. In these shocks dust has been effectively destroyed, while in the slower cloud shocks the dust destruction is incomplete until the recombination zone of the shock has been reached. These dense interstellar clouds provide a sampling of the general interstellar medium (ISM) of the LMC. Our shock analysis allows us to make a new determination of the ISM chemical composition in N, O, Ne, S, Cl, and Ar, and to obtain accurate estimates of the fraction of refractory grains destroyed. From the derived cloud shock parameters, we estimate cloud masses and show that the clouds previously existed as typical self-gravitating Bonnor–Ebert spheres into which converging cloud shocks are now being driven.

Statistical Analysis of Supernova Remnants in the Large Magellanic Cloud

Abstract We construct the most complete sample of supernova remnants (SNRs) in any galaxy—the Large Magellanic Cloud (LMC) SNR sample. We study their various properties such as spectral index (α), size, and surface brightness. We suggest an association between the spatial distribution and environment density of LMC SNRs, and their tendency to be located around supergiant shells. We find evidence that the 16 known type Ia LMC SNRs are expanding in a lower density environment compared to the Core-Collapse (CC) type. The mean diameter of our entire population (74) is 41 pc, which is comparable to nearby galaxies. We did not find any correlation between the type of SN explosion, ovality, or age. The relationship with slope a = 0.96 implies that the randomized diameters are readily mimicking such an exponent. The rate of SNe occurring in the LMC is estimated to be ∼1 per 200 yr. The mean α of the entire LMC SNR population is −0.52, which is typical of most SNRs. However, our estimates show a clear flattening of the synchrotron α as the remnants age. As predicted, the CC SNRs in our sample are significantly brighter radio emitters than type Ia remnants. We also estimate the relation for the LMC to have a slope ∼3.8, which is comparable with other nearby galaxies. We also find the residency time of electrons in the galaxy (4.0–14.3 Myr), implying that SNRs should be the dominant mechanism for the production and acceleration of CRs.

Radio-continuum study of MCSNR J0536–7038 (DEM L249)

We present a detailed radio-continuum study on Australia Telescope Compact Array (ATCA) observations of Large Magellanic Cloud (LMC) supernova remnant (SNR), MCSNR J0536-7038. This Type Ia SNR follows a horseshoe morphology, with a size 32 pc $\times$ 32 pc (1-pc uncertainty in each direction). It exhibits a radio spectrum $\alpha=-0.52\pm0.07$ between $\lambda = 73$ and 6 cm. We report detections of regions showing moderately high fractional polarisation at 6 cm, with a peak value of 71$\pm$25% and a mean fractional polarisation of 35$\pm$8%. We also estimate an average rotation measure across the remnant of -237 rad m$^{-2}$. The intrinsic magnetic field appears to be uniformly distributed, extending in the direction of the two brightened limbs of the remnant.

Multifrequency study of a new Fe-rich supernova remnant in the Large Magellanic Cloud, MCSNR J0508−6902

We present a detailed radio, X-ray and optical study of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR) which we denote MCSNR J0508-6902. Observations from the Australian Telescope Compact Array (ATCA) and the $\textit{XMM-Newton}$ X-ray observatory are complemented by deep H$\alpha$ images and Anglo Australian Telescope AAOmega spectroscopic data to study the SNR shell and its shock-ionisation. Archival data at other wavelengths are also examined. The remnant follows a filled-in shell type morphology in the radio-continuum and has a size of $\sim$74 pc $\times$ 57 pc at the LMC distance. The X-ray emission exhibits a faint soft shell morphology with Fe-rich gas in its interior $-$ indicative of a Type Ia origin. The remnant appears to be mostly dissipated at higher radio-continuum frequencies leaving only the south-eastern limb fully detectable while in the optical it is the western side of the SNR shell that is clearly detected. The best-fit temperature to the shell X-ray emission ($kT = 0.41^{+0.05}_{-0.06}$ keV) is consistent with other large LMC SNRs. We determined an O/Fe ratio of $<21$ and an Fe mass of 0.5-1.8$~M_{\odot}$ in the interior of the remnant, both of which are consistent with the Type Ia scenario. We find an equipartition magnetic field for the remnant of $\sim$28 $\mu$G, a value typical of older SNRs and consistent with other analyses which also infer an older remnant.

A SURVEY OF INFRARED SUPERNOVA REMNANTS IN THE LARGE MAGELLANIC CLOUD

We present a comprehensive infrared study of supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) using near- to mid-infrared images taken by Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8 {\mu}m) and Multiband Imaging Photometer (MIPS; 24 and 70 {\mu}m) onboard the Spitzer Space Telescope. Among the 47 bona fide LMC SNRs, 29 were detected in infrared, giving a high detection rate of 62%. All 29 SNRs show emission at 24 {\mu}m, and 20 out of 29 show emission in one or several IRAC bands. We present their 4.5, 8, 24, and 70 {\mu}m images and a table summarizing their Spitzer fluxes. We find that the LMC SNRs are considerably fainter than the Galactic SNRs, and that, among the LMC SNRs, Type Ia SNRs are significantly fainter than core-collapse SNRs. We conclude that the MIPS emission of essentially all SNRs origi- nates from dust emission, whereas their IRAC emissions originate from ionic/molecular lines, polycyclic aromatic hydrocarbons emission, or synchrotron emission. The infrared fluxes show correlation with radio and X-ray fluxes. For SNRs that have similar mor- phology in infrared and X-rays, the ratios of 24 to 70 {\mu}m fluxes have good correlation with the electron density of hot plasma. The overall correlation is explained well by the emission from collisionally-heated silicate grains of 0.1 {\mu}m size, but for mature SNRs with relatively low gas temperatures, the smaller-sized grain population is favored more. For those that appear different between infrared and X-rays, the emission in the MIPS bands is probably from dust heated by shock radiation.

Multifrequency study of SNR J0533−7202, a new supernova remnant in the LMC

We present a detailed study of Australia Telescope Compact Array (ATCA) observations of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR), SNR J0533-7202. This object follows a horseshoe morphology, with a size 37 pc x 28 pc (1-pc uncertainty in each direction). It exhibits a radio spectrum with the intrinsic synchrotron spectral index of alpha= -0.47+-0.06 between 73 and 6 cm. We report detections of regions showing moderately high fractional polarisation at 6 cm, with a peak value of 36+-6% and a mean fractional polarisation of 12+-7%. We also estimate an average rotation measure across the remnant of -591 rad m^-2. The current lack of deep X-ray observation precludes any conclusion about high-energy emission from the remnant. The association with an old stellar population favours a thermonuclear supernova origin of the remnant.