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Post Info TOPIC: Ancient LMC Supernovae


L

Posts: 131433
Date:
Imaging of N49
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Title: (Ne V) Imaging of N49 in the Large Magellanic Cloud
Authors: Cara E. Rakowski (1,2), John C. Raymond (1), Andrew H. Szentgyorgyi (1) ((1) Harvard-Smithsonian Center for Astrophysics (2) National Research Council Fellow at the Naval Research Laboratory)

We present sub-arcsecond imaging in (Ne V) of N49, the brightest optical SNR in the LMC. Between the "cool" optical and "hot" X-ray regimes, (Ne V) emission indicates intermediate temperatures for collisionally excited plasmas (2--6 x 10E5 K), for which imaging has been extremely limited. We compare the flux in these images to the O VI measured spectroscopically by FUSE in individual apertures and find dereddened line ratios that are reasonably consistent with our predictions for intermediate velocity shocks. The overall luminosity in (Ne V) for the entire remnant is 1.2E36 erg/s, which, given the measured line ratios, implies an overall O VI luminosity of 1.5E38 erg/s. These large radiative losses indicate that this material must have been shocked recently relative to the total lifetime of the remnant. We also explore the complex spatial structure. We find (Ne V) tracing the (O III) emission more closely than it does H-alpha, measure significant shifts (~0.1 pc) between the peaks of different emission lines, and find two orders of magnitude variations in the flux ratios for different filaments across the remnant. These properties as well as the general filamentary character of the optical emission suggest thermally unstable intermediate velocity shocks.

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L

Posts: 131433
Date:
DEML238 & DEML249
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Title: Dense, Fe-rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
Authors: K. J. Borkowski, S. P. Hendrick, S. P. Reynolds
(UPDATE)

We present observations of two LMC supernova remnants (SNRs), DEM L238 and DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central emission, surrounded by a faint shell, is present in both remnants. The central emission has an entirely thermal spectrum dominated by strong Fe L-shell lines, with the deduced Fe abundance in excess of solar and not consistent with the LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission originates in gas swept up and heated by the blast wave. A standard Sedov analysis implies about 50 solar masses in both swept-up shells, SNR ages between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich supernova ejecta are close to collisional ionisation equilibrium. Their presence is unexpected, because standard Type Ia SNR models predict faint ejecta emission with short ionisation ages. Both SNRs belong to a previously unrecognised class of Type Ia SNRs characterized by bright interior emission. Denser than expected ejecta and/or a dense circumstellar medium around the progenitors are required to explain the presence of Fe-rich ejecta in these SNRs. Substantial amounts of circumstellar gas are more likely to be present in explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar SNRs could be remnants of "prompt'' Type Ia explosions with young (~100 Myr old) progenitors.

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L

Posts: 131433
Date:
Shells in the Magellanic System
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Title: Shells in the Magellanic System
Authors: Snezana Stanimirovic (UW Madison)

The Magellanic System harbours >800 expanding shells of neutral hydrogen, providing a unique opportunity for statistical investigations. Most of these shells are surprisingly young, 2--10 Myr old, and correlate poorly with young stellar populations. I summarise what we have learned about shell properties and particularly focus on the puzzling correlation between the shell radius and expansion velocity. In the framework of the standard, adiabatic model for shell evolution this tight correlation suggests a coherent burst of star formation across the whole Magellanic System. However, more than one mechanism for shell formation may be taking place.

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L

Posts: 131433
Date:
Low-excitation blobs
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Title: Low-excitation blobs in the Magellanic Clouds
Authors: F. Meynadier, M. Heydari-Malayeri

Aims : We study an unknown, or very poorly known, interstellar HII component in the Magellanic Clouds. This is the first study ever devoted to this class of objects, which we call Low-excitation blobs (LEBs).
Methods : We used low-dispersion spectroscopy carried out at ESO to obtain emission line intensities of Ha, Hb, and (OIII) (4959+5007) for 15 objects in the Large Magellanic Cloud and 14 objects in the Small Magellanic Cloud. Results are displayed in excitation (oiii/Hb ratio) versus Hb luminosity diagrams.
Results : We show the presence of an LEB component in the Magellanic Clouds and study its relationship with the already known class of high-excitation blobs (HEBs). The newly found LEBs are lower excitation counterparts of HEBs and are powered by less massive exciting stars. Further study of LEBs is expected to provide new pieces of information for a better understanding the low mass end of the upper initial mass function in the Magellanic Clouds.

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L

Posts: 131433
Date:
N49
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Title: (Ne V) Imaging of N49 in the Large Magellanic Cloud
Authors: Cara E. Rakowski (1,2), John C. Raymond (1), Andrew H. Szentgyorgyi (1) ((1) Harvard-Smithsonian Center for Astrophysics (2) National Research Council Fellow at the Naval Research Laboratory)

We present sub-arcsecond imaging in (Ne V) of N49, the brightest optical SNR in the LMC. Between the "cool" optical and "hot" X-ray regimes, (Ne V) emission indicates intermediate temperatures for collisionally excited plasmas (2--6 x 10E5 K), for which imaging has been extremely limited. We compare the flux in these images to the O VI measured spectroscopically by FUSE in individual apertures and find dereddened line ratios that are reasonably consistent with our predictions for intermediate velocity shocks. The overall luminosity in (Ne V) for the entire remnant is 1.2E36 erg/s, which, given the measured line ratios, implies an overall O VI luminosity of 1.5E38 erg/s. These large radiative losses indicate that this material must have been shocked recently relative to the total lifetime of the remnant. We also explore the complex spatial structure. We find (Ne V) tracing the (O III) emission more closely than it does H-alpha, measure significant shifts (~0.1 pc) between the peaks of different emission lines, and find two orders of magnitude variations in the flux ratios for different filaments across the remnant. These properties as well as the general filamentary character of the optical emission suggest thermally unstable intermediate velocity shocks.

N49
Three-colour image of N49 in Hα (red), (O III) (green), and (Ne V) (blue). The (Ne V) image was first binned by 4 pixels then smoothed with a 1.38'' Gaussian kernel. H and [O III] were not binned but were smoothed to 0.345''. Regions from which the filament profiles were extracted are indicated.

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L

Posts: 131433
Date:
DEML238 & DEML249
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Title: Dense Fe-Rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
Authors: K. J. Borkowski, S. P. Hendrick, S. P. Reynolds

We present observations of two LMC supernova remnants (SNRs), DEM L238 and DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central emission, surrounded by a faint shell, is present in both remnants. The central emission has an entirely thermal spectrum dominated by strong Fe L-shell lines, with the deduced Fe abundance in excess of solar and not consistent with the LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission originates in gas swept up and heated by the blast wave. A standard Sedov analysis implies about 50 solar masses in both swept-up shells, SNR ages between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich supernova ejecta are close to collisional ionisation equilibrium. Their presence is unexpected, because standard Type Ia SNR models predict faint ejecta emission with short ionisation ages. Both SNRs belong to a previously unrecognized class of Type Ia SNRs characterised by bright interior emission. Denser than expected ejecta and/or a dense circumstellar medium around the progenitors are required to explain the presence of Fe-rich ejecta in these SNRs. Substantial amounts of circumstellar gas are more likely to be present in explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar SNRs could be remnants of ''prompt'' Type Ia explosions with young (~100 Myr old) progenitors.

Read more (561kb, PDF)

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L

Posts: 131433
Date:
SNR N23
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Title: Discovery of a Compact X-ray Source in the LMC Supernova Remnant N23 with Chandra
Authors: Asami Hayato (1,2), Aya Bamba (1), Toru Tamagawa (1,2), Kiyoshi Kawabata (2) ((1) RIKEN, (2) Tokyo Univ. of Sci.)

An X-ray compact source was discovered with Chandra in a supernova remnant (SNR) N23, located in the Large Magellanic Cloud. The compact source (CXOU J050552.3-680141) is seen in only the hard band (> 2 keV) image of N23, while the soft band image (< 2 keV) shows diffuse emission of the SNR, with an extent of ~60 arcsec times ~80 arcsec. The compact source is located at almost the center of N23, and there is no identifiable object for the source from previous observations at any other wavelength. The source spectrum is best explained by a power-law model with a photon index of 2.2 (1.9-2.7) and an absorption-corrected luminosity of 1.0 x 10^34 ergs s^-1 in the 0.5--10 keV band for a distance of 50 kpc. Neither pulsation nor time variability of the source was detected with this observation with a time resolution of 3.2 sec. These results correspond with those of Hughes et al. (2006) who carried out analysis independently around the same time as our work. Based on information from the best-fit power-law model, we suggest that the source emission is most likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is generally inferred that the progenitor of N23 is a core-collapsed massive star.
Based on information from the best-fit power-law model, we suggest that the source emission is most likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is generally inferred that the progenitor of N23 is a core-collapsed massive star.

SNR N23

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L

Posts: 131433
Date:
SNR 0453-68.5
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The remains of four supernovas in the nearby Large Magellanic Cloud galaxy provide a dazzling display of one of nature's most explosive events. These X-ray images show multimillion degree gas that has been heated by shock waves from the explosions. Moving in a clockwise direction from the upper left to the lower left, the approximate ages of the remnants are 600 years, 1500 years, 10,000 years and 13,000 years, respectively.


Expand (139kb, 612 x 612)
Credit NASA/CXC/SAO

Chandra X-ray spectra provide important clues as to how these stars exploded. The remnants on the upper left, upper right and lower right show a concentration of elements typical of a Type Ia supernova. Such an explosion is triggered when matter is pulled from a companion star onto a white dwarf star and pushes it past the limit of stability. The ensuing thermonuclear explosion completely disrupts the white dwarf star.

In contrast, the supernova that produced the remnant SNR 0453-68.5 left behind a neutron star. This indicates that a Type II supernova occurred when the nuclear power source of a massive star became exhausted and the stellar core collapsed to form a neutron star, while the outer layers of the star were blown away. The rapidly spinning neutron star is ejecting a magnetized wind of extremely high-energy particles, which appears in the image as the elongated, bright blue-white spot at the centre of the remnant.

Source

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L

Posts: 131433
Date:
RE: Ancient LMC Supernovae
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Title: The Chandra View of the Supernova Remnant 0506-68.0 in the Large Magellanic Cloud
Authors: John P. Hughes (1), Marc Rafelski (2), Jessica S. Warren (1), Cara Rakowski (3), Patrick Slane (3), David Burrows (4), John Nousek (4) ((1) Rutgers University, (2) UCLA, (3) Harvard-Smithsonian CfA, (4) Penn State)

A new Chandra observation of SNR 0506-68.0 (also called N23) reveals a complex, highly structured morphology in the low energy X-ray band and an isolated compact central object in the high energy band. Spectral analysis indicates that the X-ray emission overall is dominated by thermal gas whose composition is consistent with swept-up ambient material. There is a strong gradient in ambient density across the diameter of the remnant. Toward the southeast, near a prominent star cluster, the emitting density is 10 - 23 cm^-3 while toward the northwest it has dropped to a value of only 1 cm^-3. The total extent of the X-ray remnant is 100" by 120" (24 pc x 29 pc for a distance of 50 kpc), somewhat larger than previously known. The remnant's age is estimated to be ~4600 yr. One part of the remnant shows evidence for enhanced O, Ne, and perhaps Mg abundances, which is interpreted as evidence for ejecta from a massive star core collapse supernova. The compact central object has a luminosity of a few times 10^{33} ergs/s and no obvious radio or optical counterpart. It does not show an extended nebula or pulsed emission as expected from a young energetic pulsar, but resembles the compact central objects seen in other core collapse SNe, such as Cas A.

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L

Posts: 131433
Date:
LMC Planetary nebulae
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Title: Spitzer Spectra of Magellanic Cloud PNe
Authors: L. Stanghellini, P. Garcia Lario, A. Manchado, J. V. Perea Calderon, D. A. Garcia-Hernandez, R. A. Shaw, E. Villaver

Planetary nebulae (PNe) in the Magellanic Clouds (LMC, SMC) offer a unique opportunity to study both the population and evolution of low- and intermediate-mass stars in an environment which is free of the distance scale bias that hinder Galactic PN studies. The emission shown by PNe in the 5-40 Ám range is characterised by the presence of a combination of solid state features (from the dust grains) and nebular emission lines over-imposed on a strong dust continuum.
The researchers acquired low resolution IRS spectroscopy of a selected sample of LMC and SMC PNe whose morphology, size, central star brightness, and chemical composition are known. The data have been acquired and reduced, and the IRS spectra show outstanding quality as well as very interesting features.
The preliminary analysis presented here allows to determine strong correlations between gas and dust composition, and nebular morphology. More detailed analysis in the future will deepen our knowledge of mass-loss mechanism, its efficiency, and its relation to PN morphology.

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