当前超新星遗迹研究中的若干热点问题

Light Echoes and Remnants of Historically Galactic Supernovae

对银河系内历史性超新星"回光"(light echoes)的观测是研究年轻超新星遗迹的重要手段。通过对"回光"进行观测,可以确认其前身星的物理特性,揭示恒星晚期演化过程和其星周介质的三维空间分布。历史性超新星直接"回光"极其暗弱,对其探测最近几年才因新技术的应用而得以实现。综述了河内超新星遗迹包括仅有的已探测到回光现象的两颗年轻超新星遗迹——第谷(SN1572)和仙后座A(CasA)的最新研究进展。研究结果有利于更好地理解Ⅰ型和Ⅱ型超新星的性质,区别两类超新星的爆发机制,加深对超新星的核合成、重元素合成、星系形成和演化、暗能量等的了解。讨论了利用回光观测可以进一步深入开展的研究课题。

Observations to Supernova remnants（SNRs） play an important role in studying the late stellar evolution,circumstellar and interstellar medium,the Galactice Cosmic-Ray（CR）, element nucleosynthesis,galaxy evolution and so on.Based on technical update of telescopes, our knowledge on SNRs and issues related have been improved a lot in the past decade. In the paper we review major progress in the field of the young Galactic SNRs. （1） High spatial resolution X-ray observations of young SNRs by Chandra,XMM-Newton, SWIFT,SUZAKU Satellites etc give the detailed physical images of supernova explosion,nucleosynthsis, shock and CR acceleration.By using high spatial resolution images from Chandra, many pulsars associated with SNRs are found in X-rays,such as in G292.0＋1.8,G54.1＋0.3,Cassiopiea A（Cas A） and so on,which can be taken as direct evidence that these SNRs are from core-collapse supernovae（SNe）.On the other hand,the failure in finding the pulsar in Kepler＇s SNR strongly suggests that its explosion should be typeⅠa.New X-ray observations also reveal asymmetric explosion of SNe,which challenges the current theoretical calculations.It is believed that the nucleosynthesis in stellar evolution and SN explosion is in onion type with dominated elements ordered in shells following their atomic number.From the X-ray emission of ejecta dominated young SNRs,the model can be checked and the nucleosynthesis process can be well studied.The synchrotron radiations in X-rays in SNRs（e.g.a young SNR 1006,an old SNR G353.6-0.7） have been discovered,which provide the strongest evidences that the SNR shock should be one of the main CR accelerators.This is further confirmed from new very-high-energyγ-ray observations thatγ-ray emissions share same space as X-ray synchrotron emissions from the same SNR. （2） Detection of light echoes of historical SNRs unambiguously shed light on the nature of progenitors of the SNRs.I.e.The optical spectra of the light echo of young SNR Tycho 1572 confirms that it originates from the explosion of a normal typeⅠa supernova which is widely believed to come from carbon-oxygen white dwarfs that accrete mass from binary companions until they reach the Chandrasekhar limit.The discovery of both infrared and optical echoes around Cas A directly reveals that it comes from a core collapse explosion of aⅡb supernova（about 20 M_⊙） whose progenitor usually has a mass of 8-25 M_⊙. （3） We also shortly comment some key issues that have not been solved yet.Those issues could be understood with the help of new generation of radio,optical,X-ray andγ-ray missions. such as Fermi-large-AreaTelescope,Constellation-X,Symbol-X,FAST,ASKAP,etc.