Thermal Composite Supernova Remnant Research Articles

MULTI-WAVELENGTH STUDY OF THE SUPERNOVA REMNANT KES 79 (G33.6+0.1): ON ITS SUPERNOVA PROPERTIES AND EXPANSION INTO A MOLECULAR ENVIRONMENT

ABSTRACT Kes 79 (G33.6+0.1) is an aspherical thermal composite supernova remnant (SNR) observed across the electromagnetic spectrum and showing an unusual highly structured morphology, in addition to harboring a central compact object (CCO). Using the CO J = 1–0, J = 2–1, and J = 3–2 data, we provide the first direct evidence and new morphological evidence to support the physical interaction between the SNR and the molecular cloud in the local standard of rest velocity . We revisit the 380 ks XMM-Newton observations and perform a dedicated spatially resolved X-ray spectroscopic study with careful background subtraction. The overall X-ray-emitting gas is characterized by an under-ionized ( ) cool ( keV) plasma with solar abundances, plus an under-ionized ( ) hot ( keV) plasma with elevated Ne, Mg, Si, S, and Ar abundances. The X-ray filaments, spatially correlated with the 24 IR filaments, are suggested to be due to the SNR shock interaction with dense gas, while the halo forms from SNR breaking out into a tenuous medium. Kes 79 appears to have a double-hemisphere morphology viewed along the symmetric axis. Projection effect can explain the multiple-shell structures and the thermal composite morphology. The high-velocity, hot ( keV) ejecta patch with high metal abundances, together with the non-uniform metal distribution across the SNR, indicate an asymmetric SN explosion of Kes 79. We refine the Sedov age to 4.4–6.7 kyr and the mean shock velocity to 730 . Our multi-wavelength study suggests a progenitor mass of ∼15–20 solar masses for the core-collapse explosion that formed Kes 79 and its CCO, PSR J1852+0040.

GeVγ-ray EMISSION DETECTED BYFERMI-LAT PROBABLY ASSOCIATED WITH THE THERMAL COMPOSITE SUPERNOVA REMNANT KESTEVEN 41 IN A MOLECULAR ENVIRONMENT

Hadron emission from supernova remnant (SNR)-molecular cloud (MC) association systems has been widely regarded as a probe of the shock-accelerated cosmic-ray protons. Here, we report on the detection of a {\gamma}-ray emission source, with a significance of 24{\sigma} in 0.2-300 GeV, projected to lie to the northwest of the thermal composite SNR Kesteven 41, using 5.6 years of Fermi-Large Area Telescope (LAT) observation data. No significant long-term variability in the energy range 0.2--300 GeV is detected around this source. The 3{\sigma} error circle, 0.09 degree; in radius, covers the 1720MHz OH maser and is essentially consistent with the location of the V_{LSR} ~-50 km/s MC with which the SNR interacts. The source emission has an exponential cutoff power-law spectrum with a photon index of 1.9+/-0.1 and a cutoff energy of 4.0+/-0.9 GeV, and the corresponding 0.2-300 GeV luminosity is ~1.3*10^36 erg/s at a distance of 12 kpc. There is no radio pulsar in the 3{\sigma} circle responsible for the high {\gamma}-ray luminosity. While the inverse Compton scattering scenario would lead to a difficulty in the electron energy budget, the source emission can naturally be explained by the hadronic interaction between the relativistic protons accelerated by the shock of SNR Kesteven 41 and the adjacent northwestern MC. In this paper, we present a list of Galactic thermal composite SNRs detected at GeV {\gamma}-ray energies by Fermi-LAT is presented.

DYNAMICAL EVOLUTION OF SUPERNOVA REMNANTS BREAKING THROUGH MOLECULAR CLOUDS

We carry out three-dimensional hydrodynamic simulations of the supernova remnants (SNRs) produced inside molecular clouds (MCs) near their surface using the HLL code (Harten et al. 1983). We explore the dynamical evolution and the X-ray morphology of SNRs after breaking through the MC surface for ranges of the explosion depths below the surface and the density ratios of the clouds to the intercloud media (ICM). We find that if an SNR breaks out through an MC surface in its Sedov stage, the outermost dense shell of the remnant is divided into several layers. The divided layers are subject to the Rayleigh-Taylor instability and fragmented. On the other hand, if an SNR breaks through an MC after the remnant enters the snowplow phase, the radiative shell is not divided to layers. We also compare the predictions of previous analytic solutions for the expansion of SNRs in stratified media with our onedimensional simulations. Moreover, we produce synthetic X-ray surface brightness in order to research the center-bright X-ray morphology shown in thermal composite SNRs. In the late stages, a breakout SNR shows the center-bright X-ray morphology inside an MC in our results. We apply our model to the observational results of the X-ray morphology of the thermal composite SNR 3C 391.

THE METAL-ENRICHED THERMAL COMPOSITE SUPERNOVA REMNANT KESTEVEN 41 (G337.8-0.1) IN A MOLECULAR ENVIRONMENT

The physical nature of thermal composite supernova remnants (SNRs) remains controversial. We have revisited the archival XMM-Newton and Chandra data of the thermal composite SNR Kesteven 41 (Kes 41 or G337.8-0.1) and performed a millimeter observation toward this source in the $^{12}$CO, $^{13}$CO, and C$^{18}$O lines. The X-ray emission, mainly concentrated toward the southwestern part of the SNR, is characterized by distinct S and Ar He-like lines in the spectra. The X-ray spectra can be fitted with an absorbed nonequilibrium ionization collisional plasma model at a temperature of 1.3-2.6 keV and an ionization timescale of 0.1-1.2$\times$10$^{12}$ cm$^{-3}$ s. The metal species S and Ar are overabundant, with 1.2-2.7 and 1.3-3.8 solar abundances, respectively, which strongly indicate the presence of a substantial ejecta component in the X-ray-emitting plasma of this SNR. Kes 41 is found to be associated with a giant molecular cloud (MC) at a systemic local standard of rest velocity of -50 km s$^{-1}$ and confined in a cavity delineated by a northern molecular shell, a western concave MC that features a discernible shell, and an HI cloud seen toward the southeast of the SNR. The birth of the SNR in a preexisting molecular cavity implies a mass of $\gtrsim$18 M$_{\odot}$ for the progenitor if it was not in a binary system. Thermal conduction and cloudlet evaporation seem to be feasible mechanisms to interpret the X-ray thermal composite morphology, and the scenario of gas reheating by the shock reflected from the cavity wall is quantitatively consistent with the observations. An updated list of thermal composite SNRs is also presented in this paper.

G192.8-1.1: A CANDIDATE OF AN EVOLVED THERMAL COMPOSITE SUPERNOVA REMNANT REIGNITED BY NEARBY MASSIVE STARS

G192.8-1.1 has been known as one of the faintest supernova remnants (SNRs) in the Galax until the radio continuum of G192.8-1.1 is proved to be thermal by Gao et al. (2011). Yet, the nature of G192.8-1.1 has not been fully investigated. Here, we report the possible discovery of faint non-thermal radio continuum components with a spectral index <TEX>${\alpha}{\sim}0.56(S_{\nu}{\propto}{\nu}^{-{\alpha}})$</TEX> around G192.8-1.1, while of the radio continuum emission is thermal. Also, our Arecibo <TEX>$H_I$</TEX> data reveal an <TEX>$H_I$</TEX> shell, expanding with an expansion velocity of <TEX>$20-60km\;s^{-1}$</TEX>, that has an excellent morphological correlation with the radio continuum emission. The estimated physical parameters of the <TEX>$H_I$</TEX> shell and the possible association of non-thermal radio continuum emission with it suggest G192.8-1.1 to be an~0.3 Myr-old SNR. However, the presence of thermal radio continuum implies the presence of early-type stars in the same region. One possibility is that a massive star is ionizing the interior of an old SNR. If it is the case, the electron distribution assumed by the centrally-peaked surface brightness of thermal emission implies that G192.8-1.1 is a "thermal-composite" SNR, rather than a typical shell-type SNR, where the central hot gas that used to be bright in X-rays has cooled down. Therefore, we propose that G192.8-1.1 is an old evolved thermal-composite SNR showing recurring emission in the radio continuum due to a nearby massive star. The infrared image supports that the <TEX>$H_I$</TEX> shell of G192.8-1.1 is currently encountering a nearby star forming region that possibly contains an early type star(s).

ANXMM-NEWTONSTUDY OF THE MIXED-MORPHOLOGY SUPERNOVA REMNANT W28 (G6.4–0.1)

We have performed an XMM-Newton imaging and spectroscopic study of supernova remnant (SNR) W28, a prototype mixed-morphology or thermal composite SNR, believed to be interacting with a molecular cloud. The observed hot X-ray emitting plasma is characterized by low metal abundances, showing no evidence of ejecta. The X-rays arising from the deformed northeast shell consist of a thermal component with a temperature of $\sim0.3$ keV plus a hard component of either thermal (temperature $\sim 0.6$ keV) or non-thermal (photon index $=0.9$-2.4) origin. The X-ray emission in the SNR interior is blobby and the corresponding spectra are best described as the emission from a cold ($kT\sim0.4$ keV) plasma in non-equilibrium ionization with an ionization timescale of $\sim4.3\times 10^{11}$ cm$^{-3}$ s plus a hot ($kT \sim 0.8$ keV) gas in collisional ionization equilibrium. Applying the two-temperature model to the smaller central regions, we find non-uniform interstellar absorption, temperature and density distribution, which indicates that the remnant is evolving in a non-uniform environment with denser material in the east and north. The cloudlet evaporation mechanism can essentially explain the properties of the X-ray emission in the center and thermal conduction may also play a role for length scales comparable to the remnant radius. A recombining plasma model with an electron temperature of $\sim 0.6$ keV is also feasible for describing the hot central gas with the recombination age of the gas estimated at $\sim2.9\times 10^4$ yr.

XMM–Newton observations of the Galactic Centre Region – II. The soft-thermal emission

We have extended our earlier study (Heard & Warwick 2013, Paper I) of the X-ray emission emanating from the central 100 pc x 100 pc region of our Galaxy to an investigation of several features prominent in the soft X-ray (2-4.5 keV) band. We focus on three specific structures: a putative bipolar outflow from the vicinity of Sgr A*; a high surface brightness region located roughly 12 arcmin to the north-east of Sgr A*; and a lower surface-brightness extended loop feature seen to the south of Sgr A*. We show that all three structures are thermal in nature and have similar temperatures (kT ~ 1 keV). The inferred X-ray luminosities lie in the range (2 - 10) x 10^34 erg s^-1. In the case of the bipolar feature we suggest that the hot plasma is produced by the shock-heating of the winds from massive stars within the Central Cluster, possibly collimated by the Circumnuclear Disc. Alternatively the outflow may be driven by outbursts on Sgr A*, which follow tidal disruption events occurring at a rate of roughly 1 every 4000 yr. The north-east enhancement is centred on a candidate PWN which has a relatively hard non-thermal X-ray spectrum. We suggest that the coincident soft-thermal emission traces the core of a new thermal-composite supernova remnant, designated as SNR G0.13-0.12. There is no clear evidence for an associated radio shell but such a feature may be masked by the bright emission of the nearby Radio Arc and other filamentary structures. SNR G0.13-0.12 is very likely interacting with the nearby molecular cloud, G0.11-0.11, and linked to the Fermi source, 2FGL J1746.4-2851c. Finally we explore a previous suggestion that the elliptically-shaped X-ray loop to the south of Sgr A*, of maximum extent ~45 pc, represents the shell of a superbubble located in the GC region. Although plausible, the interpretation of this feature in terms a coherent physical structure awaits confirmation.

The Thermal Composite Supernova Remnant Kesteven 27 as Viewed byChandra: Shock Reflection from a Cavity Wall

We present a spatially resolved spectroscopic study of the thermal composite supernova remnant Kes 27 with Chandra. The X-ray spectrum of Kes 27 is characterized by K lines from Mg, Si, S, Ar, and Ca. The X-ray-emitting gas is found to be enriched in sulfur and calcium. The broadband and tricolor images show two incomplete shell-like features in the northeastern half and brightness fading with increasing radius to the southwest. There are over 30 unresolved sources within the remnant. None shows characteristics typical of a young neutron star. The maximum diffuse X-ray intensity coincides with a radio-bright region along the eastern border. In general, gas in the inner region is at higher temperature, and the emission is brighter, than that in the outer region. The gas in the remnant appears to be near ionization equilibrium. The overall morphology can be explained by the evolution of the remnant in an ambient medium with a density enhancement from west to east. We suggest that the remnant was born in a preexisting cavity and that the bright inner emission is due to the reflection of the initial shock from the dense cavity wall. This scenario may provide a new candidate mechanism to explain the X-ray morphology of other thermal composite supernova remnants.

A Narrow Band Chandra X-ray Analysis of SNR 3C 391

We present narrow-band and equivalent width (EW) images of the thermal composite supernova remnant (SNR) 3C 391 in the X-ray emission lines of Mg, Si and S using the Chandra ACIS Observational data. The EW images reveal the spatial distribution of the emission of the metal species Mg, Si and S in the remnant. They have a clumpy structure similar to that seen in the broadband diffuse emission, suggesting that they are largely of interstellar origin. We find an interesting finger-like feature protruding outside the southwestern radio border of the remnant, somewhat similar to the jet-like Si structure found in the famous SNR Cas A. This feature may possibly be the debris of the jet of ejecta from an asymmetrical supernova explosion of a massive progenitor star.

CHANDRA SPECTROSCOPY OF SUPERNOVA REMNANT 3C 391

We performed a spatially resolved spectroscopic study of the thermal composite supernova remnant 3C 391 by the Chandra observation. Broad- and narrow-band X-ray images show a southeast-northwest elongated morphology and unveil a highly clumpy structure of the remnant. The spectral analysis for. the small-scale features indicates normal metal abundance and uniform temperature for the interior gas. The properties of the hot gas are largely in agreement with the cloudlet evaporation model as a main mechanism for the `thermal composite` X-ray appearance, though radiative rim and thermal conduction may also be effective. An unresolved X-ray source, with a power-law spectrum, is observed on the northwest border. The equivalent width images reveal a faint finger-like protrusion in Si and S lines out of the southwest radio border.

Highly clumpy structure of the thermal composite supernova remnant 3C 391 unveiled by Chandra

The nature of the internal thermal X-ray emission seen in “thermal composite” supernova remnants is still uncertain. Chandra observation of the 3C391 shows a southeast–northwest elongated morphology and unveils a highly clumpy structure of the remnant. Detailed spatially resolved spectral analysis for the small-scale features reveals normal metal abundance and uniform temperature for the interior gas. The properties of the hot gas comparatively favor the cloudlet evaporation model as a main mechanism for the “thermal composite” X-ray appearance, though radiative rim and thermal conduction may also be effective. A faint protrusion is found in Si and S lines out of the southwest radio border.

G65.2+5.7: A Thermal Composite Supernova Remnant with a Cool Shell

This paper presents archival ROSAT PSPC observations of the G65.2+5.7 supernova remnant (also known as G65.3+5.7). Little material obscures this remnant and so it was well observed, even at the softest end of ROSAT's bandpass (~0.11 to 0.28 keV). These soft X-ray images reveal the remnant's centrally-filled morphology which, in combination with existing radio frequency observations, places G65.2+5.7 in the thermal composite (mixed morphology) class of supernova remnants. Not only might G65.2+5.7 be the oldest known thermal composite supernova remnant, but owing to its optically revealed cool, dense shell, this remnant supports the proposal that thermal composite supernova remnants lack X-ray bright shells because they have evolved beyond the adiabatic phase. These observations also reveal a slightly extended point source centered on RA = 19h 36m 46s, dec = 30deg 40' 07'' and extending 6.5 arcmin in radius in the band 67 map. The source of this emission has yet to be discovered, as there is no known pulsar at this location.

OH (1720 MHz) Masers and Mixed‐Morphology Supernova Remnants

Radio surveys of supernova remnants (SNRs) in the Galaxy have uncovered 19 SNRs accompanied by OH maser emission at 1720 MHz. This unusual class of maser sources is suggested to be produced behind a shock front from the expansion of a supernova remnant running into a molecular cloud. An important ingredient of this model is that X-ray emission from the remnant enhances the production of OH molecules. The role of X-ray emission from maser-emitting (ME) SNRs is investigated by comparing the X-ray-induced ionization rate with the theory. One aspect of this model is verified: there is a strong association between ME and mixed-morphology or thermal composite SNRs—center-filled thermal X-ray emission surrounded by shell-like radio morphology. We also present ROSAT and ASCA observations of two ME SNRs: G21.8-0.6 (Kes 69) and G357.7-0.1 (Tornado).