[论文解读] Investigations of supernovae and supernova remnants in the era of SKA

Lingzhi Wang, Xiaohong Cui+3 more|arXiv (Cornell University)|Jan 19, 2015

Radio Astronomy Observations and Technology参考文献 1被引用 4

一句话总结

本文研究了平方公里阵列（SKA）如何通过实现灵敏、高分辨率的射电巡天，彻底改变对超新星（SNe）和超新星遗迹（SNRs）的研究。研究提出，SKA无与伦比的灵敏度和大视场将探测到此前无法观测到的Ia型超新星和光学暗弱的核心坍缩超新星的射电辐射，解析SNRs中的纤维状结构以研究磁场放大和宇宙射线加速机制，并通过与CTA的多波段协同观测，解决银河系宇宙射线的起源问题。

ABSTRACT

Two main physical mechanisms are used to explain supernova explosions: thermonuclear explosion of a white dwarf(Type Ia) and core collapse of a massive star (Type II and Type Ib/Ic). Type Ia supernovae serve as distance indicators that led to the discovery of the accelerating expansion of the Universe. The exact nature of their progenitor systems however remain unclear. Radio emission from the interaction between the explosion shock front and its surrounding CSM or ISM provides an important probe into the progenitor star's last evolutionary stage. No radio emission has yet been detected from Type Ia supernovae by current telescopes. The SKA will hopefully detect radio emission from Type Ia supernovae due to its much better sensitivity and resolution. There is a 'supernovae rate problem' for the core collapse supernovae because the optically dim ones are missed due to being intrinsically faint and/or due to dust obscuration. A number of dust-enshrouded optically hidden supernovae should be discovered via SKA1-MID/survey, especially for those located in the innermost regions of their host galaxies. Meanwhile, the detection of intrinsically dim SNe will also benefit from SKA1. The detection rate will provide unique information about the current star formation rate and the initial mass function. A supernova explosion triggers a shock wave which expels and heats the surrounding CSM and ISM, and forms a supernova remnant (SNR). It is expected that more SNRs will be discovered by the SKA. This may decrease the discrepancy between the expected and observed numbers of SNRs. Several SNRs have been confirmed to accelerate protons, the main component of cosmic rays, to very high energy by their shocks. This brings us hope of solving the Galactic cosmic ray origin's puzzle by combining the low frequency (SKA) and very high frequency (Cherenkov Telescope Array: CTA) bands' observations of SNRs.

研究动机与目标

• 通过SKA卓越的灵敏度探测Ia型超新星的射电辐射，以解决其未解的前身体系统问题。
• 通过深度射电巡天探测原本暗弱且被尘埃遮蔽的核心坍缩超新星，以解决‘超新星率问题’。
• 利用高分辨率射电观测研究SNRs中磁场放大的机制和粒子加速过程。
• 利用SKA的低频能力，通过低频谱特征区分古老SNRs中质子与电子引发的射电辐射。
• 通过SKA与CTA的多波段协同观测，联合分析射电与伽马射线数据，识别银河系宇宙射线的起源。

提出的方法

• 利用SKA1-MID与SKA1-LOW的高灵敏度和大视场，开展深度、大范围的天空射电巡天。
• 应用Weiler等人（1986, 1990, 2002）的射电光变曲线模型，从超新星射电光变曲线反演质量损失率和周围介质（CSM）特性。
• 采用高分辨率（≤1角秒）成像技术，绘制SNRs中纤维状非热射电结构，以探测小于0.1 pc尺度的磁场放大现象。
• 建立质子-质子碰撞产生的次级电子的同步辐射射电谱模型，以与初级电子谱在100 MHz以下区分开来。
• 结合SKA1-LOW的低频射电数据（50–350 MHz）与CTA的高能伽马射线数据（>100 GeV），追踪SNRs中GeV–TeV能段的粒子群体。
• 利用SKA的深度成像与高灵敏度，搜索未识别伽马射线源的射电对应体。

实验结果

研究问题

• RQ1 SKA能否凭借其优于当前仪器约100倍的灵敏度，探测到当前望远镜无法观测到的Ia型超新星的射电辐射？
• RQ2 SKA1-MID/巡天将如何提升对光学暗弱且被尘埃遮蔽的核心坍缩超新星的探测能力？
• RQ3 SKA的高分辨率成像在多大程度上能解析SNRs中的纤维状结构，以研究磁场放大与粒子加速机制？
• RQ4 SKA1-LOW能否通过低频谱特征，区分古老SNRs中由初级电子与次级电子引发的射电辐射？
• RQ5 SKA与CTA观测的协同作用将如何通过识别SNRs中的粒子加速机制，帮助解决银河系宇宙射线的起源问题？

主要发现

• SKA1预计将因灵敏度提升约100倍，探测到Ia型超新星的射电辐射。
• SKA1-MID将探测到大量原本暗弱的核心坍缩超新星，显著减少预期与观测到的超新星数量之间的差异。
• 高分辨率SKA观测（≤1角秒）将在5 kpc距离处解析约0.02 pc尺度的SNRs纤维状结构，从而实现对磁场放大的详细研究。
• 古老SNRs的低频射电谱（低于100 MHz）将因次级电子贡献而出现谱特征偏离，从而可与初级电子辐射区分开来。
• SKA1-LOW与CTA的联合观测将能同步探测SNRs的低频射电与高能伽马射电辐射，为粒子加速机制提供强有力的诊断工具。
• SKA的高灵敏度将使探测未识别伽马射线源的射电对应体成为可能，有助于识别高能宇宙射线的起源。