Supernova Remnant N157B Research Articles

T-ReX: The Tarantula—Revealed by X-Rays

The Tarantula Nebula (30 Doradus, 30 Dor) is the most important star-forming complex in the Local Group, offering a microscope on starburst astrophysics. At its heart lies the exceptionally rich young stellar cluster R136, containing the most massive stars known. Stellar winds and supernovae have carved 30 Dor into an amazing display of arcs, pillars, and bubbles. We present first results and advanced data-processing products from the 2 Ms Chandra X-ray Visionary Project, “The Tarantula—Revealed by X-rays” (T-ReX). The 3615 point sources in the T-ReX catalog include massive stars, compact objects, binaries, bright pre-main-sequence stars, and compact young stellar (sub)clusters in 30 Dor. After removing point sources and excluding the exceptionally bright supernova remnant N157B (30 Dor B), the global diffuse X-ray maps reveal hot plasma structures resolved at 1–10 pc scales, with an absorption-corrected total-band (0.5–7 keV) X-ray luminosity of 2.110 × 1037 erg s−1. Spatially resolved spectral modeling provides evidence for emission lines enhanced by charge-exchange processes at the interfaces. We identify a candidate for the oldest X-ray pulsar detected to date in 30 Dor, PSR J0538-6902, inside a newly resolved arcuate X-ray wind nebula, the Manta Ray. The long temporal baseline of T-ReX allowed monitoring of dozens of massive stars, several showing periodic variability tied to binary orbital periods, and captured strong flares from at least three low-mass Galactic foreground stars.

Locating the CSM Emission within the Type Ia Supernova Remnant N103B

Abstract We present results from deep Chandra observations of the young Type Ia supernova remnant (SNR) 0509–68.7, also known as N103B, located in the Large Magellanic Cloud (LMC). The remnant displays an asymmetry in brightness, with the western hemisphere appearing significantly brighter than the eastern one. Previous multiwavelength observations have attributed the difference to a density gradient and suggested origins in circumstellar material, drawing similarities to Kepler’s SNR. We apply a clustering technique combined with traditional imaging analysis to spatially locate various emission components within the remnant. We find that O and Mg emission is strongest along the blast wave, and coincides with Spitzer observations of dust emission and optical emission from the nonradiative shocks. The abundances of O and Mg in these regions are enhanced relative to the average LMC abundances and appear as a distinct spatial distribution compared to the ejecta products, supporting the interpretation based on a circumstellar medium. We also find that the spatial distribution of Cr is identical to that of Fe in the interior of the remnant, and does not coincide at all with the O and Mg emission.

Discovery of Double-ring Structure in the Supernova Remnant N103B: Evidence for Bipolar Winds from a Type Ia Supernova Progenitor

Abstract The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509–68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distributions. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.

Imagery and UV Spectroscopy of the LMC Supernova Remnant N103B Using HST

Abstract We present Hubble Space Telescope (HST)/Wide Field Camera 3 multiband imagery of N103B, which is the remnant of a SN Ia in the Large Magellanic Cloud, as well as HST/Cosmic Origins Spectrograph (COS) ultraviolet spectroscopy of the brightest radiatively shocked region. The images show a wide range of morphology and relative emission-line intensities, from smooth Balmer-line dominated collisionless shocks that are due to the primary blast wave to clumpy radiative shock filaments that are due to secondary shocks in density enhancements. The COS data show strong FUV line emissions, despite a moderately high extinction along this line of sight. We use the COS data with previous optical spectra to constrain the shock conditions, we refine the abundance analysis, and we find abundances that are typical of the local interstellar medium within the uncertainties. Under an assumption that the material being shocked was shed from the pre-supernova system, this finding places constraints on any significant enrichment in that material, and thus on the non-degenerate star in what was presumably a single-degenerate SN Ia.

Molecular Clouds Associated with the Type Ia SNR N103B in the Large Magellanic Cloud

Abstract N103B is a Type Ia supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out new 12CO(J = 3–2) and 12CO(J = 1–0) observations using ASTE and ALMA. We have confirmed the existence of a giant molecular cloud at V LSR ∼ 245 km s−1 toward the southeast of the SNR using ASTE 12CO(J = 3–2) data at an angular resolution of ∼25″ (∼6 pc in the LMC). Using the ALMA 12CO(J = 1–0) data, we have spatially resolved CO clouds along the southeastern edge of the SNR with an angular resolution of ∼1.″8 (∼0.4 pc in the LMC). The molecular clouds show an expanding gas motion in the position–velocity diagram with an expansion velocity of ∼5 km s−1. The spatial extent of the expanding shell is roughly similar to that of the SNR. We also find tiny molecular clumps in the directions of optical nebula knots. We present a possible scenario that N103B exploded in the wind-bubble formed by the accretion winds from the progenitor system, and is now interacting with the dense gas wall. This is consistent with a single-degenerate scenario.

Integral Field Spectroscopy of Balmer-dominated Shocks in the Magellanic Cloud Supernova Remnant N103B

Abstract We present results of integral field spectroscopy of Balmer-dominated shocks in the LMC supernova remnant (SNR) N103B, carried out using the Wide Field Integral Spectrograph (WiFeS ) on the 2.3 m telescope at the Siding Spring Observatory in Australia. Existing X-ray studies of N103B have indicated an SN Ia origin. Radiative shock emission from clumpy material surrounding the SNR may result from interaction of the forward shock with relic stellar wind material, possibly implicating a thermonuclear explosion in a single-degenerate binary system. The recently discovered Balmer-dominated shocks mark the impact of the forward shock with low density, partially neutral CSM gas, and form a partial shell encircling clumps of material exhibiting radiative shocks. The WiFeS spectra of N103B reveal broad Hα emission having a width as high as 2350 km s−1 along the northern rim, and both Hα and Hβ broad profiles having widths around 1300 km s−1 along the southern rim. Fits to the Hα line profiles indicate that in addition to the usual broad and narrow emission components, a third component of intermediate width exists in these Balmer-dominated shocks, ranging from around 125 km s−1 up to 225 km s−1 in width. This is consistent with predictions of recent Balmer-dominated shock models, which predict that an intermediate-width component will be generated in a fast neutral precursor. We derive a Sedov age of approximately 685 ± 20 years for N103B from the Balmer-dominated spectra, consistent with the young age of 380–860 years estimated from light echo studies.

Progenitor type identification for supernova remnant N103B in the Large Magellanic Cloud by Suzaku and Chandra observations

Abstract This paper presents a detailed analysis of supernova remnant (SNR) N103B located in the Large Magellanic Cloud (LMC), based on Suzaku and Chandra observations. The spectrum of the entire remnant was closely reproduced by using three interstellar medium (ISM) components with temperatures of ∼ 0.32, ∼ 0.56, and ∼ 0.92 keV and one ejecta component with ∼ 3.96 keV, based on a spectral analysis of the Suzaku/X-ray Imaging Spectrometer (XIS) data. The ejecta was overabundant in heavy elements, such as Mg, Si, S, Ca, Fe, and Ni. The unprecedentedly high quality of data obtained with Suzaku/XIS allowed us to correctly distinguish between two emissions from the ISM and the ejecta for the first time in a spectral analysis. Combining the spectral analysis of XIS data with the image analysis based on Chandra/Advanced CCD Imaging Spectrometer (ACIS) data, we verified that the ejecta distributions for elements from Si to Fe-K were similar to one another, although the Fe-K emission was located slightly inward compared with that of the lighter elements such as Si, S, Ar, and Ca. We compared hydrogen-rich ejecta plasma (called “H-dominated plasma”), which is indicative of Type II SNRs, with plasma rich in heavy elements and poor in hydrogen (called “pure metal plasma”) mainly observed in Type Ia SNRs. High-energy continuum images in the 5.2–6.0 keV band obtained with ACIS were extremely similar to those of the ejecta, implying that the origin of the high-energy continuum might indeed be the ejecta. By combining spectral analyses and high-energy continuum images, we found some indications for H-dominated plasma, and showed, that the progenitor of N103B might have been a Type II supernova. The progenitor mass was estimated to be 13 M⊙ based on the abundance patterns of Mg, Fe, and Ni relative to Si.

CANGAROO‐III Search for Gamma Rays from SN 1987A and the Surrounding Field

Optical images of SN 1987A show a triple ring structure. The inner (dust) ring has recently increased in brightness and in the number of hot spots suggesting that the supernova shock wave has collided with the dense pre-existing circumstellar medium, a scenario supported by radio and X-ray observations. Such a shocked environment is widely expected to result in the acceleration of charged particles, and the accompanying emission of very high energy gamma-rays. Here, we report the results of observations made in 2004 and 2006 which yield upper limits on the TeV gamma-ray flux, which are compared with a theoretical prediction. In addition, we set upper limits on the TeV flux for four high energy objects which are located within the same field of view of the observation: the super-bubble 30 Dor C, the Crab-like pulsar PSR B0540$-$69, the X-ray binary LMC X-1, and the supernova remnant N157B.

ChandraACIS Spectroscopy of N157B: A Young Composite Supernova Remnant in a Superbubble

We present a Chandra ACIS observations of N157B, a young supernova remnant (SNR) located in the 30 Doradus star formation region of the Large Magellanic Cloud. This remnant contains the most energetic pulsar known (PSR J053747.39-691020.2; Ė = 4.8 × 1038 ergs s-1), which is surrounded by a X-ray-bright nonthermal nebula that likely represents a toroidal pulsar wind terminal shock observed edge-on. Two of the eight pointlike X-ray sources detected in the observation are shown to have near-IR and optical counterparts (within 05 offsets), which are identified as massive stellar systems in the Cloud. We confirm the nonthermal nature of the comet-shaped X-ray emission feature and show that the spectral steepening of this feature away from the pulsar is quantitatively consistent with synchrotron cooling of shocked pulsar wind particles flowing downstream at a bulk velocity close to the speed of light. Around the cometary nebula we unambiguously detect a spatially resolved thermal component, which accounts for about 1/3 of the total 0.5-10 keV flux from the remnant. This thermal component is distributed among various clumps of metal-enriched plasma embedded in the low surface brightness X-ray-emitting diffuse gas. The relative metal enrichment pattern suggests that the mass of the supernova progenitor is 20 M☉. A comparison of the X-ray data with Hubble Space Telescope optical images now suggests that the explosion site is close to a dense cloud, against which a reflection shock is launched. The interaction between the reflected material and the nebula has likely produced both its cometary shape and the surrounding thermal emission enhancement. SNR N157B is apparently expanding into the hot low-density interior of the surrounding superbubble formed by the young OB association LH 99, as revealed by Spitzer mid-infrared images. This scenario naturally explains the exceptionally large sizes of both the thermal and nonthermal components, as well as the lack of an outer shell of the SNR. However, the real situation in the region is likely to be more complicated. We find that a partially round soft X-ray-emitting clump with distinct spectral properties may result from a separate oxygen-rich remnant. These results provide a rare glimpse into the SNR structure and evolution in a region of recent star formation.

AChandraACIS Study of 30 Doradus. I. Superbubbles and Supernova Remnants

We present an X-ray tour of diffuse emission in the 30 Doradus star-forming complex in the Large Magellanic Cloud using high spatial resolution X-ray images and spatially resolved spectra obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. The dominant X-ray feature of the 30 Doradus nebula is the intricate network of diffuse emission generated by interacting stellar winds and supernovae working together to create vast superbubbles filled with hot plasma. We construct maps of the region showing variations in plasma temperature (T = 3-9 million degrees), absorption [NH = (1-6) × 1021 cm-2], and absorption-corrected X-ray surface brightness [SX = (3-126) × 1031 ergs s-1 pc-2]. Enhanced images reveal the pulsar wind nebula in the composite supernova remnant N157B, and the Chandra data show spectral evolution from nonthermal synchrotron emission in the N157B core to a thermal plasma in its outer regions. In a companion paper we show that R136, the central massive star cluster, is resolved at the arcsecond level into almost 100 X-ray sources. Through X-ray studies of 30 Doradus the complete life cycle of such a massive stellar cluster can be revealed.

The Radial Structure of Supernova Remnant N103B

We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals subarcsecond structure, in both the brightness and spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy, using a plane-parallel, nonequilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (net > 1012 s cm-3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (net ~ 1011 s cm-3) O, Ne, and Mg component. To reproduce the strong Fe Kα line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization timescale (net ~ 1010.8 s cm-3) component. This hot Fe might be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate-mass species are consistent with model prediction for Type Ia events.

Detection of an X‐Ray Pulsar Wind Nebula and Tail in SNR N157B

We report Chandra X-ray observations of the supernova remnant N157B in the Large Magellanic Cloud, which are presented together with an archival Hubble Space Telescope optical image and a radio continuum map for comparison. This remnant contains the recently discovered 16 ms X-ray pulsar PSR J0537-6910, the most rapidly rotating young pulsar known. Using phase-resolved Chandra imaging, we pinpoint the location of the pulsar at 5h37m4736, -69°10'204 (J2000), with an uncertainty of 1''. PSR J0537-6910 is not detected in any other wavelength band. The X-ray observations resolve three distinct features: the pulsar itself, a surrounding compact wind nebula that is strongly elongated (dimensions of ~0.6 × 1.7 pc), and a feature of large-scale (5 pc long) diffuse emission trailing from the pulsar. This latter comet-tail-shaped feature coexists with enhanced radio emission and is oriented nearly perpendicular to the major axis of the pulsar wind nebula. We propose the scenario below to explain these features. The bright, compact nebula is likely to be powered by a toroidal pulsar wind of relativistic particles that is partially confined by the ram pressure from the supersonic motion of the pulsar. The particles, after being forced out from the compact nebula (the head of the comet), are eventually dumped into a bubble (the tail), which is primarily responsible for the extended diffuse X-ray and radio emission. The ram-pressure confinement also allows a natural explanation for the observed X-ray luminosity of the compact nebula and for the unusually small X-ray to spin-down luminosity ratio of ~0.2%, compared to similarly energetic pulsars. We estimate the pulsar wind Lorentz factor of N157B to be ~4 × 106 (with an uncertainty of a factor of ~2), consistent with that inferred from the modeling of the Crab Nebula.

Radio Properties of the Supernova Remnant N157B

A new investigation of the supernova remnant (SNR) N157B was carried out with the Australia Telescope Compact Array. Radio continuum images of the entire 30 Doradus region have been made at 3.5 and 6 cm wavelengths with a resolution of ~2''. These data allow a high-resolution study of the spectral index distribution and polarization properties of both N157B and the nearby 30 Doradus nebula (the latter will be reported in a subsequent paper). N157B is an extended Crab-type SNR which may be beginning the transition to a composite remnant. There is little apparent fine structure, and the brightest radio region is several parsecs from the probable position of the X-ray pulsar. The SNR has a radio spectral index of -0.19 and is significantly polarized at 3.5 cm but not at longer wavelengths.

Search for an Optical Counterpart of PSR J0537–6910

AbstractWe have conducted an optical study of the recently discovered very fast (P∼16msec) X-ray pulsar PSR J0537-6910 in the supernova remnant N157B. Broad band imaging has been obtained to study the field around the X-ray position and a high speed photometry programme was carried out in an attempt to detect optical pulses.

Intensive X-ray Monitoring of the 16ms Crab-like Pulsar PSR J0537 – 6910

AbstractThe recently discovered pulsar PSR J0537-6910 is the most rapidly rotating young pulsar known. This latest example of a Crab-like pulsar, located in the supernova remnant N157B in the Large Magellanic Cloud, is rotating twice as fast as the Crab pulsar. With a characteristic age of 5000 years, it is also the oldest known example of a Crab-like pulsar and was likely rotating close to the maximum rate for a neutron star when it was born. Here we report preliminary results from an intensive monitoring campaign of X-ray observations acquired with the Rossi X-ray Timing Explorer that began in January 1999. These observation have revealed a large glitch event in the pulse timing during the first six month of our campaign, consistent with those suggested by sparse observations dating back to 1993. The current evolution of the rotation rate of PSR J0537-6910 provides a unique probe of the internal structure of neutron stars and constraints on possible pulsar emission mechanisms.

X-ray Spectroscopy of the Supernova Remnant N103B

We report and interpret a new, 100 ks X-ray observation of the supernova remnant N103B obtained by the ASCA Observatory.

ITAL]ROSAT[/ITAL] HRI Detection of the 16 [CLC]ms[/CLC] Pulsar PSR J0537−6910 Inside Supernova Remnant N157B

Based on a deep ROSAT HRI observation, we have detected a pulsed signal in the 0.1-2 keV band from PSR J0537-6910, the recently discovered pulsar associated with the supernova remnant N157B in the Large Magellanic Cloud. The measured pulse period 0.01611548182 s ± 0.02 ns, epoch MJD 50,540.5, gives a revised linear spin-down rate of 5.1271 × 10−14 s s-1, which is slightly greater than the previously derived value. The narrow pulse shape (FWHM ~ 10% duty cycle) in the ROSAT band resembles those seen in both RXTE and ASCA data ( 2 keV), but there is also marginal evidence for an interpulse. This ROSAT detection enables us to locate the pulsar at R.A.=5h37m472, decl.=-69°10'23'' (J2000). With its uncertainty ~3'', this position coincides with the centroid of a compact X-ray source. But the pulsed emission accounts for only ~10% of the source luminosity of ~2 × 1036 ergs-1 in the 0.1-2 keV band. These results support our previous suggestions: (1) the pulsar is moving at a high velocity ( ~103 km s-1); (2) a bow shock, formed around the pulsar, is responsible for most of the X-ray emission from the source; and (3) a collimated outflow from the bow shock region powers a pulsar wind nebula that accounts for an elongated nonthermal radio and X-ray feature to the northwest of the pulsar.

Quasi‐normal Modes of Rotating Relativistic Stars: Neutral Modes for Realistic Equations of State

We compute zero-frequency (neutral) quasi-normal f-modes of fully relativistic and rapidly rotating neutron stars, using several realistic equations of state (EOSs) for neutron star matter. The zero-frequency modes signal the onset of the gravitational radiation-driven instability. We find that the l=m=2 (bar) f-mode is unstable for stars with gravitational mass as low as 1.0 - 1.2 M_\odot, depending on the EOS. For 1.4 M_\odot neutron stars, the bar mode becomes unstable at 83 % - 93 % of the maximum allowed rotation rate. For a wide range of EOSs, the bar mode becomes unstable at a ratio of rotational to gravitational energies T/W \sim 0.07-0.09 for 1.4 M_\odot stars and T/W \sim 0.06 for maximum mass stars. This is to be contrasted with the Newtonian value of T/W \sim 0.14. We construct the following empirical formula for the critical value of T/W for the bar mode, (T/W)_2 = 0.115 - 0.048 M / M_{max}^{sph}, which is insensitive to the EOS to within 4 - 6 %. This formula yields an estimate for the neutral mode sequence of the bar mode as a function only of the star's mass, M, given the maximum allowed mass, M_{max}^{sph}, of a nonrotating neutron star. The recent discovery of the fast millisecond pulsar in the supernova remnant N157B, supports the suggestion that a fraction of proto-neutron stars are born in a supernova collapse with very large initial angular momentum. Thus, in a fraction of newly born neutron stars the instability is a promising source of continuous gravitational waves. It could also play a major role in the rotational evolution (through the emission of angular momentum) of merged binary neutron stars, if their post-merger angular momentum exceeds the maximum allowed to form a Kerr black hole.

Discovery of an Ultrafast X-Ray Pulsar in the Supernova Remnant N157B

We present the serendipitous discovery of 16 ms pulsed X-ray emission from the Crab-like supernova remnant N157B in the Large Magellanic Cloud. This is the fastest spinning pulsar associated with a supernova remnant (SNR). Observations with the Rossi X-Ray Timing Explorer (RXTE), centered on the field containing SN 1987A, reveal an X-ray pulsar with a narrow pulse profile. The archival Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray data confirm this detection and locate the pulsar within 1' of the supernova remnant N157B, 14' from SN 1987A. The pulsar shows evidence of glitch(es) between the 3.5 yr separating the RXTE and ASCA observations; the mean linear spin-down rate is =5.126×10−14 s s−1. The background-subtracted, pulsed emission is similar to other Crab-like pulsars with a power law of photon index ~1.6. The characteristic spin-down age (~5000 yr) is consistent with the previous age estimate of the SNR. The inferred B-field for a rotationally powered pulsar is ~1×1012 G. Our result confirms the Crab-like nature of N157B ; the pulsar is likely associated with a compact X-ray source revealed by ROSAT HRI observations.

ROSATandASCAObservations of the Crab‐like Supernova Remnant N157B in the Large Magellanic Cloud

We report the results of ROSAT and ASCA X-ray observations of the supernova remnant N157B (or 30 Dor B, SNR 0539-69.1) in the Large Magellanic Cloud. For comparison, we also briefly describe the results on SNR 0540-69.3, the only confirmed Crab-like remnant in the Cloud. The X-ray emission from N157B can be decomposed into a bright comet-shaped feature, superimposed on a diffuse emission region of a dimension $\sim 20$ pc. The flat and nearly featureless spectrum of the remnant is distinctly different from those of young shell-like remnants, suggesting a predominantly Crab-like nature of N157B. Characterized by a power law with an energy slope $\sim 1.5$, the spectrum of N157B above $\sim 2$ keV is, however, considerably steeper than that of SNR 0540-69.3, which has a slope of $\sim 1.0$. At lower energies, the spectrum of N157B presents marginal evidence for emission lines, which if real most likely arise in hot gas of the diffuse emission region. The hot gas has a characteristic thermal temperature of 0.4-0.7 keV. No significant periodic signal is detected from N157B in the period range of $3 \times 10^{-3}-2000$ s. The pulsed fraction is $\lesssim 9%$ (99% confidence) in the $2-7$ keV range. We discuss the nature of the individual X-ray components. In particular, we suggest that the synchrotron radiation of relativistic particles from a fast-moving ($\sim 10^3 km s^{-1}$) pulsar explains the size, morphology, spectrum, and energetics of the comet-shaped X-ray feature. We infer the age of the remnant as $\sim 5 \times 10^3$ yrs. The lack of radio polarization of the remnant may be due to Faraday dispersion by foreground \ion{H}{2} gas.