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Post Info TOPIC: Ancient LMC Supernovae


L

Posts: 131433
Date:
N44
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A Surprisingly Bright Superbubble

682935main_n1929_665.jpg

This composite image shows a superbubble in the Large Magellanic Cloud (LMC), a small satellite galaxy of the Milky Way located about 160,000 light years from Earth. Many new stars, some of them very massive, are forming in the star cluster NGC 1929, which is embedded in the nebula N44, so named because it is the 44th nebula in a catalogue of such objects in the Magellanic Clouds. The massive stars produce intense radiation, expel matter at high speeds, and race through their evolution to explode as supernovas. The winds and supernova shock waves carve out huge cavities called superbubbles in the surrounding gas. X-rays from NASA's Chandra X-ray Observatory (blue) show hot regions created by these winds and shocks, while infrared data from NASA's Spitzer Space Telescope (red) outline where the dust and cooler gas are found. The optical light from the 2.2-m Max-Planck-ESO telescope (yellow) in Chile shows where ultraviolet radiation from hot, young stars is causing gas in the nebula to glow.
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Posts: 131433
Date:
SNR 0453-68.5
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Title: SNR 0453-68.5: An Asymmetric Remnant and its Plerion in the Large Magellanic Cloud
Authors: Randall L. McEntaffer, Thomas Brantseg, Morgan Presley

We present a comprehensive study of the X-ray emission from SNR 0453-68.5 in the Large Magellanic Cloud (LMC) as seen from the Chandra X-ray Observatory. This object is in a class of composite remnants that exhibit a shell of emission surrounding a central plerion, more commonly known as a pulsar wind nebula (PWN). This is one of only five remnants in the LMC with an identified PWN. We find that the shell of emission is not ejecta dominated, but rather due to shocked ISM that has been swept up by the supernova blast wave or located in a precursor cavity wall. This is supported by the morphology of the local molecular cloud as seen with the Spitzer Space Telescope. The spectral properties are consistent with a middle-aged remnant >17000 years old. A point source detected within the central knot is determined to be the pulsar powering the synchrotron emission of the PWN. Spectral fits show the nebula is well characterized by a power law with photon index \Gamma=2.0. This index is constant over a spatial scale of 0.4-1.2 pc, which is inconsistent with younger PWN containing remnants such as the Crab Nebula and SNR 0540-69.3. These fits also contain significant contributions from an ejecta dominated thermal plasma which we interpret as evidence of mixing during an evolved interaction of the PWN with the reverse shock of the SNR. We observe no evidence that the central pulsar contains a significant velocity transverse to the line of sight and argue that despite the asymmetric surface brightness distribution the SN explosion giving birth to this remnant may have been quite symmetric.

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Posts: 131433
Date:
RE: Ancient LMC Supernovae
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Title: An X-Ray Study of Supernova Remnant N49 and Soft Gamma-Ray Repeater 0526-66 in the Large Magellanic Cloud
Authors: Sangwook Park (UT Arlington), John P. Hughes (Rutgers), Patrick O. Slane (Harvard-Smithsonian CfA), David N. Burrows (Penn State), Jae-Joon Lee (KASI), Koji Mori (Miyazaki)

We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet" beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the detected Si-rich ejecta may represent explosive O-burning or incomplete Si-burning products from deep interior of the supernova. On the other hand, the observed Si/S abundance ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age of N49, tau_Sed ~ 4800 yr, with the explosion energy E_0 ~ 1.8 x 10^51 erg. Our blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR 0526-66 indicates that the PL photon index (Gamma ~ 2.5) is identical to that of PSR 1E1048.1-5937, the well-known candidate transition object between anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model implies X-ray emission from a small (R ~ 1 km) hot spot(s) (kT ~ 1 keV) in addition to emission from the neutron star's cooler surface (R ~ 10 km, kT ~ 0.4 keV). There is a considerable discrepancy in the estimated column toward 0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral models would be crucial to test the long-debated physical association between N49 and 0526-66.

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Posts: 131433
Date:
LHA 120-N 44
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A Cosmic Superbubble

eso1125a.jpg

ESO's Very Large Telescope captured this striking view of the nebula around the star cluster NGC 1929 within the Large Magellanic Cloud, a satellite galaxy of our own Milky Way. A colossal example of what astronomers call a superbubble dominates this stellar nursery. It is being carved by the winds from bright young stars and the shockwaves from supernova explosions.
The Large Magellanic Cloud is a small neighbouring galaxy to the Milky Way. It contains many regions where clouds of gas and dust are forming new stars. One such region, surrounding the star cluster NGC 1929, is shown in close-up in this new image from ESO's Very Large Telescope. This nebula is officially known as LHA 120-N 44, or just N 44 for short. Hot young stars in NGC 1929 are emitting intense ultraviolet light and causing the gas to glow. This effect highlights the aptly-named superbubble, a vast shell of material around 325 by 250 light-years across. For comparison, the nearest star to our Sun is just over four light-years distant.

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Posts: 131433
Date:
SNR 0509-67.5
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A delicate sphere of gas, photographed by NASA's Hubble Space Telescope, floats serenely in the depths of space. The pristine shell, or bubble, is the result of gas that is being shocked by the expanding blast wave from a supernova. Called SNR 0509-67.5 (or SNR 0509 for short), the bubble is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud (LMC), a small galaxy about 160,000 light-years from Earth. Ripples in the shell's surface may be caused by either subtle variations in the density of the ambient interstellar gas, or possibly driven from the interior by pieces of the ejecta. The bubble-shaped shroud of gas is 23 light-years across and is expanding at more than 5,000 kilometres per second).
Hubble's Advanced Camera for Surveys observed the supernova remnant on Oct. 28, 2006, with a filter that isolates light from glowing hydrogen seen in the expanding shell. These observations were then combined with visible-light images of the surrounding star field that were imaged with Hubble's Wide Field Camera 3 on Nov. 4, 2010.

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Position (J2000): RA 05 09 31.70, Dec -67 31' 18".01

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Posts: 131433
Date:
Supernova Remnant N23
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Title: Suzaku Observations of the Supernova Remnant N23 in the Large Magellanic Cloud
Authors: Kentaro Someya, Aya Bamba, Manabu Ishida

X-ray emission from the supernova remnant N23 in the Large Magellanic Cloud (LMC) is studied using the X-ray Imaging Spectrometer (XIS) onboard Suzaku. Thanks to superior energy resolution of the XIS in the soft X-ray band, we resolved H-like and He-like Oxygen K\alpha emission lines from N23 with unprecedentedly high quality, and as a result, identified a new optically thin thermal emission component with a temperature ~0.2 keV, as well as that with a temperature of ~0.5-0.7 keV previously known. This alters the estimate of the ionisation timescale net from ~10^{10-11} cm^-3s to >~10^{12} cm^{-3}s. Under the assumption that N23 is still in the Sedov phase, its age evaluated from the newly discovered low temperature component is ~8000 yr, although it is possible that N23 has already moved into the radiative phase. The abundances of the heavy elements are found to be roughly consistent with those of the LMC average, which indicates that the origin of the X-ray emission of N23 is swept-up ambient material, as expected from its ionisation timescale.

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Posts: 131433
Date:
SNR B0536-69.3
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Stellar debris created the Honeycomb nebula

Since it was first discovered in 1992, the curious shape of the Honeycomb Nebula, which lurks in a nearby galaxy called the Large Magellanic Cloud, has been a puzzle.
As it floats in an area of the LMC racked by the explosions of numerous supernovae in recent cosmic history, one theory was that the pattern might be caused by a set of localised ripples created when clumps of debris from an ancient supernova were hit by a blast wave from a relatively recent one.

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Position (2000): RA 05 35 44, Dec -69 17.9

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Posts: 131433
Date:
RE: Ancient LMC Supernovae
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n49.jpg

N49: Stellar Shrapnel Seen in Aftermath of Explosion

This beautiful composite image shows N49, the aftermath of a supernova explosion in the Large Magellanic Cloud. A new long observation from NASA's Chandra X-ray Observatory, shown in blue, reveals evidence for a bullet-shaped object being blown out of a debris field left over from an exploded star.
In order to detect this bullet, a team of researchers led by Sangwook Park of Penn State University used Chandra to observe N49 for over 30 hours. This bullet can be seen in the bottom right hand corner of the image (roll your mouse over the image above) and is rich in silicon, sulphur and neon. The detection of this bullet shows that the explosion that destroyed the star was highly asymmetric.
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Posts: 131433
Date:
Supernova Remnants
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typingsnrs_420.jpg
Credit: NASA/CXC/UCSC/L. Lopez et al.

These two supernova remnants are part of a new study from NASA's Chandra X-ray Observatory that shows how the shape of the remnant is connected to the way the progenitor star exploded. In this study, a team of researchers examined the shapes of 17 supernova remnants in both the Milky Way galaxy and a neighbour galaxy, the Large Magellanic Cloud.
The results revealed that one category of supernova explosion, known as "Type Ia," generated a very symmetric, circular remnant. This type of supernova is thought to be caused by a thermonuclear explosion of a white dwarf, and is often used by astronomers as a "standard candle" for measuring cosmic distances. The image in the right panel, the so-called Kepler supernova remnant, represents this type of supernova.

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Posts: 131433
Date:
LMC HII Complex N44
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Title: Spitzer View of Young Massive Stars in the LMC HII Complex N44
Authors: C.-H. Rosie Chen (1,2), You-Hua Chu (2), Robert A. Gruendl (2), Karl D. Gordon (3), Fabian Heitsch (4) ((1) U of Virginia, (2) U of Illinois, (3) StScI, (4) U of Michigan)

The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images. We have modelled the SEDs of 36 YSOs that appear single or dominant within a group. We find good fits for Types I and I/II YSOs,but Types II and II/III YSOs show deviations between their observed SEDs and models that do not include PAH emission. We have also found that some Type III YSOs have central holes in their disk components. YSO counterparts are found in four ultracompact HII regions and their stellar masses determined from SED model fits agree well with those estimated from the ionisation requirements of the HII regions. The distribution of YSOs is compared with those of the underlying stellar population and interstellar gas conditions to illustrate a correlation between the current formation of O-type stars and previous formation of massive stars. Evidence of triggered star formation is also presented.

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