XMM-Newton study of 30 Dor C and a newly identified MCSNR J0536-6913 in the Large Magellanic Cloud

Aims: We present a study of the superbubble (SB) 30 Dor C and the newly identified MCSNR J0536-6913 in the LMC. Methods: All available XMM-Newton data (exposure times of 420 ks EPIC-pn, 556 ks EPIC-MOS1, 614 ks EPIC-MOS2) were used to characterise the thermal X-ray emission in the region. An analysis of the non-thermal X-rays is also presented and discussed in the context of emission mechanisms previously suggested in the literature. These data are supplemented by X-ray data from Chandra, optical data from the MCELS, and radio data from ATCA and MOST. Results: The brightest thermal emission was found to be associated with a new supernova remnant, MCSNR J0536-6913. X-ray spectral analysis of MCSNR J0536-6913 suggested an ejecta-dominated remnant with lines of O, Ne, Mg, and Si, and a total 0.3-10 keV luminosity of ~8E+34 erg/s. Based on derived ejecta abundance ratios, we determined the mass of the stellar progenitor to be either ~18 M_sun or as high as >40 M_sun, though the spectral fits were subject to assumptions (e.g., uniform temperature and well-mixed ejecta). The thermal emission from the SB exhibited enrichment by alpha-process elements, evidence for a recent core-collapse SNR interaction with the SB shell. We detected non-thermal X-ray emission throughout 30 Dor C, with the brightest regions being highly correlated with the H-alpha and radio shells. We created a non-thermal spectral energy distribution for the north-eastern shell of 30 Dor C which was best-fit with an exponentially cut-off synchrotron model. Conclusions: Thermal X-ray emission from 30 Dor C is very complex, consisting of a large scale SB emission at the eastern shell wall with the brightest emission due to MCSNR J0536-6913. The fact that the non-thermal spectral energy distribution of the SB shell was observed to roll-off is further evidence that the non-thermal X-rays from 30 Dor C are synchrotron in origin.Comment: 22 pages, 21 figures, accepted for publication in Astronomy and Astrophysic

The Supergiant Shell LMC2: II. Physical Properties of the 10^6 K Gas

LMC2 has the highest X-ray surface brightness of all know supergiant shells in the Large Magellanic Cloud (LMC). The X-ray emission peaks within the ionized filaments that define the shell boundary, but also extends beyond the southern border of LMC2 as an X-ray bright spur. ROSAT HRI images reveal the X-ray emission from LMC2 and the spur to be truly diffuse, indicating a hot plasma origin. We have obtained ROSAT PSPC and ASCA SIS spectra to study the physical conditions of the hot gas interior to LMC2 and the spur. Raymond-Smith thermal plasma model fits to the X-ray spectra, constrained by HI 21-cm emission-line measurements of the column density, show the plasma temperature of the hot gas interior of LMC2 to be kT = 0.1 - 0.7 keV and of the spur to be kT = 0.1 - 0.5 keV. We have compared the physical conditions of the hot gas interior to LMC2 with those of other supergiant shells, superbubbles, and supernova remnants (SNRs) in the LMC. We find that our derived electron densities for the hot gas inside LMC2 is higher than the value determined for the supergiant shell LMC4, comparable to the value determined for the superbubble N11, and lower than the values determined for the superbubble N44 and a number of SNRs.Comment: 29 pages, 5 figures, to be published in Ap

The population of X-ray supernova remnants in the Large Magellanic Cloud

We present a comprehensive X-ray study of the population of supernova remnants (SNRs) in the LMC. Using primarily XMM-Newton, we conduct a systematic spectral analysis of LMC SNRs to gain new insights on their evolution and the interplay with their host galaxy. We combined all the archival XMM observations of the LMC with those of our Very Large Programme survey. We produced X-ray images and spectra of 51 SNRs, out of a list of 59. Using a careful modelling of the background, we consistently analysed all the X-ray spectra and measure temperatures, luminosities, and chemical compositions. We investigated the spatial distribution of SNRs in the LMC and the connection with their environment, characterised by various SFHs. We tentatively typed all LMC SNRs to constrain the ratio of core-collapse to type Ia SN rates in the LMC. We compared the X-ray-derived column densities to HI maps to probe the three-dimensional structure of the LMC. This work provides the first homogeneous catalogue of X-ray spectral properties of LMC SNRs. It offers a complete census of LMC SNRs exhibiting Fe K lines (13% of the sample), or revealing contribution from hot SN ejecta (39%). Abundances in the LMC ISM are found to be 0.2-0.5 solar, with a lower [$\alpha$/Fe] than in the Milky Way. The ratio of CC/type Ia SN in the LMC is $N_{\mathrm{CC}}/N_{\mathrm{Ia}} = 1.35(_{-0.24}^{+0.11})$, lower than in local SN surveys and galaxy clusters. Comparison of X-ray luminosity functions of SNRs in Local Group galaxies reveals an intriguing excess of bright objects in the LMC. We confirm that 30 Doradus and the LMC Bar are offset from the main disc of the LMC, to the far and near sides, respectively. (abridged)Comment: Accepted for publication in Astronomy and Astrophysics. 54 pages, 18 figures, 12 tables. The resolution of the figures has been reduced compared to the journal version; v2: New title, minor text edits; v3: Correct version

Supernova Remnants in the Magellanic Clouds. IV. X-Ray Emission from the Largest SNR in the LMC

We present the first X-ray detection of SNR 0450-70.9 the largest known supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical images and high-dispersion spectra, and radio continuum maps. Optical images of SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments along the eastern and western rims and within the shell interior. The interior filaments have higher [S II]/Halpha ratios and form an apparent inner shell morphology. The X-ray emission region is smaller than the full extent of the optical shell, with the brightest X-ray emission found within the small interior shell and on the western rim of the large shell. The expansion velocity of the small shell is ~220 km/s, while the large shell is ~120 km/s. The radio image shows central brightening and a fairly flat radio spectral index over the SNR. However, no point X-ray or radio source corresponding to a pulsar is detected and the X-ray emission is predominantly thermal. Therefore, these phenomena can be most reasonably explained in terms of the advanced age of the large SNR. Using hydrodynamic models combined with a nonequilibrium ionization model for thermal X-ray emission, we derived a lower limit on the SNR age of about 45,000 yr, well into the later stages of SNR evolution. Despite this, the temperature and density derived from spectral fits to the X-ray emission indicate that the remnant is still overpressured, and thus that the development is largely driven by hot gas in the SNR interior.Comment: Accepted for publication in The Astrophysical Journa

Multi-frequency 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

Chandra Observation of the Magellanic Cloud Supernova Remnant 0454-672 in N9

A Chandra observation has defined the extent of the SNR B 0454-692 in the LMC H II region N9. The remnant has dimension 2.3" x 3.6" and is elongated in the NS direction. The brightest emission comes from a NS central ridge which includes three bright patches. There is good agreement between X-ray and [O III] and [S II] morphology. The remnant is old enough so that optical data give more information about dynamics than do the X-ray data. The SN energy release was >= 4 x 10^50 ergs and the age is ~3 x 10^4 years. There are several unresolved sources nearby but none are clearly associated with the remnant. The X-ray spectrum is soft and indicates enhanced Fe abundance in the central region, consistent with a Type Ia SN origin, but a Type II origin cannot be ruled out.Comment: AASTeX, 20 pages including 5 figures. Accepted for publication in The Astrophysical Journal. Figures have been reduced in resolution for space requirements; full-resolution figures may be requested by email to [email protected]

HST/WFPC2 and VLT/ISAAC observations of PROPLYDS in the giant HII region NGC 3603

We report the discovery of three proplyd-like structures in the giant HII region NGC 3603. The emission nebulae are clearly resolved in narrow-band and broad-band HST/WFPC2 observations in the optical and broad-band VLT/ISAAC observations in the near-infrared. All three nebulae are tadpole shaped, with the bright ionization front at the head facing the central cluster and a fainter ionization front around the tail pointing away from the cluster. Typical sizes are 6,000 A.U. x 20,000 A.U. The nebulae share the overall morphology of the proplyds (``PROto PLanetarY DiskS'') in Orion, but are 20 to 30 times larger in size. Additional faint filaments located between the nebulae and the central ionizing cluster can be interpreted as bow shocks resulting from the interaction of the fast winds from the high-mass stars in the cluster with the evaporation flow from the proplyds. The striking similarity of the tadpole shaped emission nebulae in NGC 3603 to the proplyds in Orion suggests that the physical structure of both types of objects might be the same. We present 2D radiation hydrodynamical simulations of an externally illuminated star-disk-envelope system, which was still in its main accretion phase when first exposed to ionizing radiation from the central cluster. The simulations reproduce the overall morphology of the proplyds in NGC 3603 very well, but also indicate that mass-loss rates of up to 10^-5 Mo/yr are required in order to explain the size of the proplyds. (abbreviated)Comment: 10 pages, 4 Postscript figures, uses emulateapj.sty and psfig.tex. Astronomical Journal, in press (January 2000 issue

The Hourglass Nebulae of Sher 25 and SN 1987 A: Two of a Kind?

We have performed a detailed study of the morphology and kinematics of the hourglass-shaped nebula around the blue supergiant Sher 25 in the galactic giant HII region NGC 3603. Near-infrared high resolution adaptive optics images in the Br gamma line and HST/NICMOS images in the HeI 1.08mu line were compared with iso-velocity maps in the H alpha and [NII] lines. The adaptive optics observations clearly resolved the width of the ring (0.9", i.e., 0.027 pc), yielding delta R / R = 1:8. We show that the H alpha and [NII] lines trace the entire silhouette of the hourglass. The bipolar lobes of the hourglass expand at 70 km/s, whereas the ring around the waist of the hourglass expands at 30 km/s. Both the ring and the bipolar lobes have about the same dynamical age, indicating a common origin and a major outburst and mass-loss event 6630 yr ago. The ionized mass within the hourglass is between 0.3 Mo and 0.6 Mo - quite comparable to the total mass suggested for the expanding (pre-supernova) shell around SN 1987 A. The hourglass structure around Sher 25 is similar to that of SN 1987 A in spatial extent, mass, and velocities. The major differences between these two nebulae might arise from environmental effects. Both internal and external ionization sources are available for Sher 25's nebula. Furthermore, Sher 25 and its hourglass-shaped nebula appear to be moving to the south-west with respect to the ambient interstellar medium, and ram pressure has apparently deformed the hourglass. We conclude that the circumstellar nebulae around SN 1987 A and Sher 25 are very similar and define a new class of nebulae around blue supergiants in their final evolutionary stage.Comment: 9 pages, Latex, also available at ftp://ftp.astro.uiuc.edu/pub/brandner/sher25_apjl or at http://www.astro.uiuc.edu/~brandner/pub.html , accepted for publication in ApJ Letter