基于空时显著性的日冕物质抛射检测

日冕物质抛射(Coronal Mass Ejection, CME)是一种剧烈的太阳爆发现象, 它会对行星际空间造成严重扰动, 进而影响人类生产、生活. 基于CME的时空显著性, 将显著性检测方法引入到CME检测中, 利用结构化矩阵分解SOHO (Solar and Heliospheric Observatory)的大角度光谱日冕仪(Large Angle and Spectrometric Coronagraph Experiment, LASCO) C2的日冕图像对应的特征矩阵, 从中恢复出稀疏部分获得显著前景. 然后考虑CME运动时产生的时间显著性, 从而去除非CME结构(如冕流), 得到最终检测结果. 实验表明, 以人工目录协调数据分析中心(Coordinated Data Analysis Workshop, CDAW)检测结果为基准时, 所提方法不仅在检测CME数量上比计算机辅助跟踪软件包(Computer Aided CME Tracking Software package, CACTus)和太阳爆发事件检测系统(Solar Eruptive Event Detection System, SEEDS)有优势, 还在CME中心角度和张角宽度等特征物理参数测量上比CACTus和SEEDS更接近CDAW目录参考值.     

The magnetic field strength and energy flux of energetic electrons in a microwave burst source region

The observations of a microwave burst with multiple impulses on 1993 Oct 2, 073940–074100 UT are analysed. This event consists of multiple impulses superimposed on a slowly varying burst background. Our formula for coronal magnetic field diagnostics was used here for the first time to derive the field strength and information on the energetic electrons. The results are: 1) The mean spectral index of the impulsive component in the optically thin part is less than that of the slow background by 1 (a harder spectrum). The mean brightness temperature at 19.6 GHz of the former is 6 times that of the latter. 2) The mean magnetic strengths of the impulse and slow burst regions are 158 G and 531 G, respectively. The time variation in the slow burst region is saddle-shaped, being 50% lower in the middle than at the beginning and end. 3) The column density NL and number density N of energetic electrons in the impulsive component are 4% and 8% of those of the slow component, but the energy flux and emission coefficient are 100% and 800% greater. The two components appear to be produced by two different electron groups with different energy distributions in two different regions.     

部分遮蔽类星体SDSS J151653.22+190048.2的紫外波段中等宽度发射线起源

类星体SDSS J151653.22+190048.2 (简称J1516+1900)在紫外-光学-近红外波段展现出奇特的光谱性质:其光学Hα、Hβ和近红外的Paα、Paβ等发射线的半高全宽(full width at half maximum intensity, FWHM)均超过5000 km/s,等值宽度接近类星体平均值;而紫外波段光谱的常见发射线Lyβ、OVI、Lyα、NV、Si IV和CIV等,由FWHM1700 km/s的中等宽度成分主导.这种现象很可能是由于紫外发射线的宽线成分经尘埃消光,强度严重削弱,从而使得中等宽度成分凸显出来;在光学和近红外波段,尘埃消光减弱,发射线由宽线成分主导,潜在的中等宽度成分不容易被看到.根据中等宽度成分的线宽和J1516+1900中央超大质量黑洞的质量MBH5.75×108M⊙,在维里化假设下,估计中等宽度发射区到中央黑洞的距离约为1.6 pc.另一方面,利用J1516+1900丰富的观测谱线,结合光致电离模型计算,可以限定J1516+1900的中等宽度发射线区气体密度1012cm-3、电离参数10-0.65.据此估计该发射线区到中心黑洞距离0.016 pc,只有维里化距离的1%.这一矛盾结果预示着中等宽度发射区可能具有较为复杂的物理结构,未来需要观测更多类似J1516+1900的部分遮蔽类星体并进行系统的分类和研究.     

ASO-S中文专辑: 序言

先进天基太阳天文台(ASO-S)是我国第一个获得批准立项的太阳空间探测卫星任务.本专辑共包含了14篇文章,着重介绍了卫星平台和有效载荷在研制过程中的一些重要的方面和具体的细节.本中文专辑的14篇文章和ASO-S卫星英文专辑的13篇文章,构成了ASO-S卫星从科学到仪器乃至分析方法较为完整的系统性介绍.     

冕流电流片的白光和紫外观测研究

日冕电流片是日冕磁重联发生的主要区域, 这一过程将磁能转化为等离子体的热能和动能. 通过选取大角度光谱日冕仪(Large Angle and Spectrometric Coronagraph, LASCO)的白光与远紫外日冕成像光谱仪(Ultraviolet Coronagraph Spectrometer, UVCS)的紫外观测, 研究了2003年1月3日观测到的冕流电流片. LASCO C2白光数据显示电流片中的等离子体团在视场中可从60km·s^-1加速至340km·s^-1, 加速度为 60m·s^-2; 假设视向深度为0.3--1.5R_⊙, 得到所研究电流片在UVCS狭缝高度处的平均电子数密度约为(1.52--7.60)×10⁷cm^-3. 对沿UVCS视场狭缝分布的[Fe xviii ] 974 ? A和Lyα谱线强度进行研究, 发现电流片处的[Fe xviii ]谱线强度比周围明显增大, 计算得到所研究时段内电流片的电子温度范围为(2.94–4.04)×10⁶K; 而在电流片处的Lyα谱线强度相对周围变化不大, 在电流片内部两侧强度比中心略高, 可能的主要原因是电流片内部中心处等离子体的运动速度要比两侧快, 这使得中心比两侧有更强的多普勒暗化作用. 以UVCS观测的Lyα和[Fe xviii ]谱线的辐射强度比和计算的电子温度为约束条件, 发现当狭缝电流片处等离子体运动速度约为237–254 km·s ^?1 时, 通过理论计算的Lyα和[Fe xviii ]谱线的辐射发射率比值和观测谱线强度比值相当. 在该速度范围内, 电流片内部Lyα辐射的碰撞项约为辐射项的42%–57%. 此事件中的冕流电流片比通常情形下的冕流电流片中等离子体温度更高、运动速度更大, 可能的原因在于其南侧爆发的两个日冕物质抛射促进了电流片中的磁重联过程, 更多的磁能释放用于等离子体的加热和加速. 所得研究结果可以为我国将要发射的先进天基太阳天文台(Advanced Space-based Solar Observatory, ASO-S)未来的资料处理提供重要参考.     

ASO-S卫星工程LST爆发模式触发和终止方案

先进天基太阳天文台(ASO-S)是计划于2021年底或2022年上半年发射的中国首颗综合性太阳探测卫星,莱曼阿尔法太阳望远镜(LST)作为ASO-S的有效载荷之一,具体包括莱曼阿尔法全日面成像仪(SDI)、日冕仪(SCI)以及白光望远镜(WST) 3台科学仪器和2台导行镜(GT),其主要目标是在多个波段对太阳上的两类剧烈爆发现象(太阳耀斑和日冕物质抛射)进行连续不间断的高分辨率观测.为了实现这一观测目标, LST所有仪器的观测模式中均包含了一种针对爆发事件而设置的爆发模式.该模式下, SCI将以更高的频率进行图像采集, SDI和WST则以更高的频率对爆发所在区域进行图像采集.测试结果表明,观测图像经过中值滤波、像元合并处理后,可以通过监测图像各像元亮度的相对变化提取爆发事件的时间和位置信息.这些信息将为LST观测模式间的相互切换提供重要电子学输入.     

A Parametric Survey of the CME Triggering Process by Numerical Simulations

Observations indicate that solar coronal mass ejections (CMEs) are closely associated with reconnection-favored flux emergence, which was explained in the emerging flux trigger mechanism for CMEs by Chen & Shibata based on numerical simulations. We present a parametric survey of the triggering agent: its polarity orientation, position, and the amount of the unsigned flux. The results suggest that whether a CME can be triggered depends on both the amount and location of the emerging flux, in addition to its polarity orientation. A diagram is presented to show the eruption and non-eruption regimes in the parameter space. The work is aimed at providing useful information for the space weather forecast.     

Study of the fast X-ray transient XTE J1901+014 based on INTEGRAL,RXTE, and ROSAT data

The source XTE J1901+014 discovered by the RXTE observatory during an intense outburst of hard radiation and classified as a fast X-ray transient is studied. The source’s spectral characteristics in the quiescent state have been investigated for the first time both in the soft X-ray energy range (3–20 keV) based on ROSAT and RXTE data and in the hard energy range (>20 keV) based on INTEGRAL data. A timing analysis of the source’s properties has revealed weak nonperiodic bursts of activity on time scales of several tens of seconds and two intense (～0.5–1 Crab) outbursts more than several hundred seconds in duration. Certain assumptions about the nature of the object under study are made.     

Photon Spectroscopy with Imaging X-Ray Instruments

Individual X-ray photons in the keV energy range produce hundreds of photoelectrons in a single pixel of a CCD array detector. The number of photoelectrons produced is a linear function of the photon energy, allowing the measurement of spectral information with an imaging detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and Hinode/XRT, use CCD detectors in an integrating mode and are designed to make temperature estimates from multiband filter photometry. We show how such instruments can be used in a new way to perform a limited type of this photon spectroscopy. By measuring the variance in intensity of a series of repeated images through a single filter of an X-ray source, the mean energy per detected photon can be determined. This energy is related to the underlying coronal spectrum, and hence it can be used to deduce the mean plasma temperature. We apply this technique to data from the Yohkoh Soft X-Ray Telescope and compare the temperatures obtained with this technique with the temperatures derived using the standard filter ratio method for a postflare loop system. Given the large dynamic range of the soft X-ray flux observed from the Sun, we describe the requirements for a future instrument that would be better suited to performing photon spectroscopy. B.J. Labonte deceased 24 October 2005.     

TeV Gamma Rays From the Galactic Center Direct and Indirect Links to the Massive Black Hole in Sgr A

The recent detection of TeV gamma-radiation from the direction of the Galactic Center within several arc-minutes around Sgr A^* is the first model-independent evidence of existence of high-energy particle accelerator(s) in the central 10 pc region of our Galaxy. This is an extraordinary site that harbours many remarkable objects with the compact radio source Sgr A^* – a hypothetical super-massive black hole (SMBH) – in the dynamical center of the Galaxy. Here we explore the possible direct and indirect links of the reported TeV emission to the SMBH. We show that at least three γ-ray production scenarios that take place close to the event horizon of the SMBH can explain the reported TeV fluxes. An alternative (or additional) channel of TeV radiation is related to the run-away protons accelerated in Sgr A^*. Quasi-continuous injection of relativistic protons into the surrounding dense gas environment initiates detectable high-energy gamma-ray emission. The absolute flux and the energy spectrum of this radiation component strongly depend on the history of particle injection and the character of diffusion of protons during the last 10⁵ yr. For a reasonable combination of a few model parameters, one can explain the detected gamma-ray flux solely by this diffuse component.