Supernova Remnants In The Molecular Environments

Born in giant molecular clouds (MCs), massive stars evolve from collapsing molec-ular cores to core-collapse supernovae. During their short lifetimes, they evacuate a cavity with their energetic winds and ionizing radiation. If there are MCs in the envi-ronment, we may be able to observe supernova remnants (SNRs) contacting the molec-ular gas on the cavity wall. The interaction between SNRs and MCs plays an important role in investigating the dynamical evolution of the shocked gas, studying SNRs and their progenitors, and exploring cosmic rays’hadronic interaction.My PhD thesis mainly focuses on investigating the SNRs Kes78, Kes79, and W28in the molecular environment by using multi-wavelength observations, and studying the relation between the molecular cavity and the progenitor mass.Starting from SNR Kes78, we investigated the molecular environment of Kes78and performed an XMM-Newton X-ray spectroscopic study for the northeastern shell of the remnant. Using the observations of CO’s three transitions, we established the evidences for the interaction between the remnant and the～81km s-1molecular cavity, which include the broadened12CO-line profiles and the elevated12CO J=2-1/J=1-0ratios. We also showed the distribution of the MCs, which will lead further studies on the hadronic γ-ray emission. The X-rays arising from the northeastern radio shell are emitted by under-ionized hot (～1.5keV), low-density (-0.1cm-3) plasma, and the plasma may be of inter-cloud origin. The age of the remnant is inferred to be about6kyr. The size of the molecular cavity in Kes78implies an initial mass around22M⊙for the progenitor. The cavity and arc shape of the MCs surrounding SNRs inspired us that the stellar wind of the progenitor stars may shape to the MCs and which may help us to under-stand the progenitor mass. We have found a linear relationship between the size of a massive star’s main-sequence bubble in a molecular environment and the star’s initial mass:Rb≈1.22M/M⊙-9.16pc. Since stars in the mass range of8to25-3OM⊙will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molec-ular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the progenitor masses of supernova remnants (SNRs) that are discovered to evolve in molecular cavities. We have used this method to estimate the initial masses of the progenitors of eight SNRs:Kes69, Kes75, Kes78,3C396,3C397, HC40, Vela, and RX J1713-3946.Thermal composite SNRs are often found to be associated with MCs. There are a lot of interesting but unkown observational properties of these SNR, which attracts many observations and studies in recent years. As the prototype of thermal compos-ite SNRs, the nature of W28’s mixed-morphology is still unclear. We have performed an XMM-Newton imaging and spectroscopic study of SNR W28. The X-ray emis-sion in the SNR interior is blobby and the corresponding spectra are best described as the emission from a cold plasma in non-equilibrium ionization plus a hot gas in collisional ionization equilibrium. The evaporated cloud material may be responsible to the cold component of the two-temperature model. Couldlet evaporation is an in-dispensable process to produce the centrally-filled X-ray morphology. Applying the two-temperature model to the smaller central regions, we find non-uniform interstel-lar 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. A recombining plasma model with an electron temperature of0.6keV is also feasi-ble for describing the hot central gas with the recombining age of the gas estimated at～2.9×104yr. The X-rays arising from the deformed northeast shell consist of a thermal component with a temperature of-0.3keV plus a hard component of either thermal (temperature-0.61keV) or non-thermal (photon index-2) origin. Non-thermal bremsstrahlung radiation produced by electrons suffering Coulomb losses is the most plausible explanation for the non-thermal X-ray.We provide kinetic evidences of the thermal composite SNR Kes79interacting with the MCs at～105km s-1by performing CO observations. Kes79in X-ray band consists many bright filaments and a faint, diffuse halo. The global X-ray emission is described by a two-temperature (0.23+1.05keV) model, with over-abundant S and Ar shown in the hot component, suggesting the existence of ejecta. We have found an X-ray cloud with distinguished high temperature (2.0-0.4+0.5keV) and large abundances of Mg, Si, S and Ar. Unlike the filamentary structures; the abundances of the faint halo has solar, or even sub-solar metal abundances. At the edge area of the halo, the X-ray spectra can be reproduced with a single hot component (0.9-1.4keV). We study the evolution of the SNR and obtain a shock velocity of833-12+3km s-1, an age of～5.8kyr. The double shell structure and the thermal composite morphology of Kes79can be explained by projection effect based on multi-wavelength study. According to the size of the molecular cavity and the abundances of metal species in the ejecta, the progenitor star of the remnant is estimated to be a B1star with a mass of～12M⊙We discovered a transient3XMM J185246.6+003317serendipitously south to the SNR Kes79when we study the remnant. The spin-down rate of the pulsar is <1.1×10-13s s-1, which, together with the long period11.5587126(4) s, indicates a dipolar surface magnetic field of<3.6×1013G, a characteristic age of>1.7Myr, and a spin-down luminosity of<2.8×1030erg s-1. Its X-ray spectrum is best-fitted with a resonant cyclotron scattering model and also can be adequately described by a blackbody model. The observations covering a seven-month span from2008to2009show variations in the spectral properties of the source, with the luminosity decreasing from2.7×1034erg s-1to4.6×1033erg s-1,along with a decrease of the black-body temperature from≈0.8keV to≈0.6keV. The X-ray luminosity of the source is higher than its spin-down luminosity, ruling out rotation as a power source. The combined timing and spectral properties, the non-detection of any optical or infrared counterpart, together with the lack of detection of the source in archival X-ray data prior to the2008XMM-Newton observation, point to3XMM J185246.6+003317be-ing a newly discovered transient low-B magnetar undergoing an outburst decay during the XMM-Newton observations. The non-detection by Chandra in2001sets an upper limit of4×1032erg s-1to the quiescent luminosity of3XMM J185246.6+003317. Its period is the longest among currently known transient magnetars. The foreground absorption toward3XMM J185246.6+003317is similar to that of Kes79, suggesting a similar distance of～7.1kpc. It is of interest to know that whether there is a connection between the magnetar, SNR Kes79and the anti-magnetar embedded in the SNR. The conclusive answer, however, will need future observations.