presentation 致密天体与弥漫介质课件

星际闪烁和散射,星际介质对信号传播的影响,星际介质分布在恒星和恒星之间，包括星际气体、星际尘埃、宇宙线与星际磁场。 星际介质对地球上所接受天体辐射信号的影响： 1. 色散展宽(DM) 2. 散射 3. 法拉第旋转(Faraday Rotation) 4. 星际闪烁(Scintillation) 由一定尺度上的介质非均匀性引起,脉冲星星际介质的探针,脉冲星辐射是动态的信号：色散展宽，电子柱密度。 散射：导致轮廓展宽 脉冲星辐射具有偏振：法拉第旋转探测星际磁场分布。 脉冲星辐射被限制限制在很小的角径范围，近似点光源：星际闪烁。,2019/3/18,4,Pulsar Workshop, 2009, Beijng,色 散,散射 导致脉冲轮廓展宽,2019/3/18,5,Pulsar Workshop, 2009, Beijng,2019/3/18,6,Pulsar Workshop, 2009, Beijng,散射 导致脉冲轮廓展宽,星际磁场引起的 法拉第旋转旋转量RM,星际闪烁,2019/3/18,8,Pulsar Workshop, 2009, Beijng,经过薄屏后信号的相位和幅度的变化,展宽角径 散射展宽,2019/3/18,Pulsar Workshop, 2009, Beijng,9,薄屏模型可以较好地符合大部分观测现象,星际闪烁,Apparent source diameters,2019/3/18,10,Pulsar Workshop, 2009, Beijng,星际介质在空间的分布,空间分布理论模型,其中q=1/a为波数，湍流扰动尺度的倒数。 ：视线方向电子密度平均空间湍动强度。,=11/3：Kolmogorov谱 当 4 时，陡谱模型 ( Bandford & Narayan 1985 ) 内尺度模型（inner scale）(Coles et al. 1987),2019/3/18,12,Pulsar Workshop, 2009, Beijng,星际介质在空间的分布,薄屏模型：不均匀区的典型大小为a，厚度为D，各处的折射率不同，是随机分布的，平均折射率接近于1。,厚屏模型：弥漫于脉冲星与观测者之间,2019/3/18,13,Pulsar Workshop, 2009, Beijng,散射理论：等效屏模型,脉冲星星际闪烁,衍射式闪烁: Scheuer 1968; Rickett, 1969 星际介质小空间尺度:1081010 cm; 特征时标 ： 1/D 几分钟到几小时， 消相干带宽 : 1/D 100 KHz到几十MHz;,折射式闪烁：Sieber 1982; Rickett, 1984 星际介质大空间尺度:10121014 cm; 特征时标：几天到几月甚至年; D 1 长期流量变化 对衍射式闪烁的有关特征量例如特征时间，特征带宽，漂移模式等有调制作用。,4,4,Kolmogorov谱 (=11/3)：,描述DISS动态谱(薄屏模型) Theory prediction of DISS parameters (Thin scattering screen model),2019/3/18,16,Pulsar Workshop, 2009, Beijng,曲线变化,V iss: Pulsar transverse velocities derived from diffractive scintillation spectra：,Gupta (1994):,18,Thin screen,2019/3/18,Pulsar Workshop, 2009, Beijng,19,=4,=11/3: Kolmogorov fluctuation spectrum,u=sF/sd : describe the scattering strength sF is the Fresnel scale at the scattering disk at which the geometric phase difference is 1 radian compared to the direct path; sd is a scale at the observer at which the average phase changes is 1 radian. u1: strong scattering,2019/3/18,Pulsar Workshop, 2009, Beijng,21,流量变化和调制指数,2019/3/18,22,Pulsar Workshop, 2009, Beijng,2019/3/18,Pulsar Workshop, 2009, Beijng,23,For nearby pulsars, the modulation is weak, and DISS will be main effect. For Kolmogorov spectrum, mu5/6 m1 For larger DM, DISS effect is weaker, and m DM-1. But RISS is stronger, with m u-1/3. (u D, so m DM-1/3),Oral presentation at IAUC 182 Submitted to CJAA,d : d: Diffractive scintillation(DISS): short narrow Refractive scintillation(RISS): long wide,五颗脉冲星在1540 MHz的长期星际闪烁监测,每9天观测一次，数据2001年1月2002年6月 积分26hr，子积分24min 被观测脉冲星： PSR B0329+54 PSR B1823+26 PSR B1929+10 PSR B2020+28 PSR B2021+51,闪烁研究,Wang, N.; Manchester, R. N.; Johnston, S.; Rickett, Bet al.: 2005, MNRAS, 358, 270,2019/3/18,25,Pulsar Workshop, 2009, Beijng,PSR B0329+54 的动态谱,DM26.8 pc cm-3 D = 1.06 kpc 3 hr 的观测 结果： td10-30 min d 5-15 MHz,2019/3/18,26,Pulsar Workshop, 2009, Beijng,二维自相关分析,二维自相关 特征时间和特征频率,闪烁二维动态谱,2019/3/18,28,Pulsar Workshop, 2009, Beijng,二维自相关函数,2019/3/18,29,Pulsar Workshop, 2009, Beijng,2019/3/18,Pulsar Workshop, 2009, Beijng,30,Modelling ACFs for PSR B0329+54,strong scattering thin disk Kolmogorov spectrum,闪烁参数与频率的依赖关系,a. Bhat, Rao & Gupta 1999 b. Gupta, Rickett & Lyne 1994 c. Stinebring, Fainon & Mckinnon 1996 d. Our results,2019/3/18,32,Pulsar Workshop, 2009, Beijng,Daily Observations of Interstellar Scintillation in PSR B0329+54,Obs: Mar 1231, 2004,Wang, N.; Yan, Z.; Manchetser, R. N. et al.: 2008, MNRAS,Daily Observations of Interstellar Scintillation in PSR B0329+54,调制系数,对于Kolmogorov 谱，调制系数的理论值,调制系数理论和观测的对比,Modulation indices,Observed prediction !,闪烁参数的互相关 Cross correlation,Wang, N.; Yan, Z.; Manchetser, R. N. et al.: 2008, MNRAS, accepted,二次谱 Secondary Spectra, Two dimensional FFT of dynamic spectrum,Observing the structure of central image !,2019/3/18,Pulsar Workshop, 2009, Beijng,40,Kolmogorov Spectrum =3.67,折射式衍射特征时间,Theory prediction:,Structure Function,衍射式星际闪烁的参量,TC93模型 Taylor & Cordes 1993,NE2001模型 Cordes & Lazio 2003 a,b,2019/3/18,45,Pulsar Workshop, 2009, Beijng,闪烁和自行速度的相关性,Harrison & Lyne 1993,Gupta 1995,2019/3/18,46,Pulsar Workshop, 2009, Beijng,Putney & Stinebring 2006,2019/3/18,47,Pulsar Workshop, 2009, Beijng,2019/3/18,48,Pulsar Workshop, 2009, Beijng,脉冲星的自行速度 脉冲星闪烁速度 银河系星际电子密度模型,Putney & Stinebring 2006,据已知的脉冲星速度和距离得到的脉冲星闪烁速度的期望值。,Gupta 1995,