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脉冲星和快速射电暴距离模型及太阳偏离银盘距离的研究
Alternative TitlePulsar and FRB distance model and theSun’s offset from the Galactic plane
姚菊枚
Subtype博士
Thesis Advisor王娜 ; R.N.Manchester 教授
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline天体物理
Keyword星际介质 结构 电子密度 脉冲星距离 太阳位置 银盘
Abstract天体距离的估计通常很困难,但是距离是最基本的参数。脉冲星具有两种距离,非模型依赖的距离(或非色散量依赖的距离)和依赖电子密度模型的距 离(或依赖色散量的距离)。基于脉冲星非模型依赖距离,色散量(DM)以及 一个简单的模型来模拟星系际介质(IGM),我们建立了一个新的电子密度模型来描述自由电子密度在银河系、麦哲伦云以及星系际介质的分布。新的电子密度模型可用于估计具有色散量测量的脉冲星以及快速射电暴(FRB)的距离。具有非模型依赖距离或模型距离的年轻脉冲星的z向分布可用于计算太阳偏离银盘的距离。分析太阳相对银盘的位置是对电子密度模型的一个应用。 新电子密度模型,称为YMW16,主要描述电子密度在银河系、麦哲伦云 以及星系际介质的分布。银河系部分包含了延展的厚盘成分,用于描述热的星际介质,薄盘成分用于描述分子环的电子密度分布,旋臂成分基于最近的氢二区数据的拟合,银心成分,以及七个靠近太阳的成分,古姆星云(Gum Nebula),银河系的一号圈(Loop I)和银河系本地泡(Local Bubble)等。太阳对银盘的偏离以及银河系外围的翘曲(Warp)结构已经包含在YMW16模型 中。银河系成分参数的拟合依赖于189颗具有非模型依赖距离以及色散量的脉冲星数据。我们使用简单的模型描述电子密度在麦哲伦云以及星系际介质的分 布。对于189颗脉冲星,86颗脉冲星的模型距离在非模型依赖距离的误差范围 内,38颗脉冲星模型距离在20%的误差范围内。整体来说,在95%的置信区间内模型距离的误差小于90%。与之前的NE2001和TC93模型相比,YMW16模型 有很大的提高。由星际散射导致的脉冲星以及快速射电暴的延迟时标(或展宽时标),可以由模型估测得到。 太阳的位置不在银盘上,而是朝北银极方向偏离银盘。通过分析年轻脉冲星的z向分布,我们计算了太阳离银盘的距离(z☉)。脉冲星的非模型依赖距离 可由三角视差、动力学、成协关系以及伴星的光学观测获得,对于没有距离信息的脉冲星,模型距离依赖于两个电子密度模型NE2001和YMW16。通过对描述等温自束缚盘双曲函数的累积分布函数的拟合,我们获得了Z☉和标高H的值,其对应误差由自举方法(Bootstrap method)获得。我们采用离太阳4.5 kpc范围内的年轻脉冲星来分析脉冲星年龄对Z☉和标高H的影响,其样本对应的特征年龄上限逐渐减小且各个样本都剔除了受本地旋臂和银河系外围翘曲结构影响的脉冲星。根据距离种类,有以下三类距离数据:非模型依赖距离、非模型依赖距离和依赖NE2001的模型距离以及非模型依赖距离和依赖YMW16的模型距离。我们发现脉冲星年龄上限小于105.75 yr且模型距离基于YMW16的样本给出最优的结果,Z☉值的误差最小且H的值逐渐趋于平行。依据这一包含了115颗脉冲星的样本,我们获得z☉ = 13.4士4.4 pc和H=56.9士6.5 pc,其标高的值约等于OB星以及疏散星团星的标高。基于另外两组数据,非模型依赖距离以及非模型依赖距离和依赖NE2001的模型距离,给出了基本相似的结果。
Other AbstractDistances to astronomical objects are often difficult to estimate, but are of fundamental significance. Pulsars have two kinds of distances, independent distances and model distances. On basis of pulsar independent distance, pulsar dispersion measure (DM) and a simple model for intergalactic medium (IGM) we construct a new model for the distribution of free electron density in the Galaxy, the Magellanic Clouds (MCs) and IGM that can be used to estimate distance to pulsars and fast radio bursts (FRBs) with DM. Distances to pulsars without independent distances could be derived from electron density model, and the analysis of z-distribution of young pulsars is used to calculate Sun’s offset from the Galactic plane. To analyse Sun’s offset is one of the applications of the new electron density model. The new electron density model, hereafter referred as YMW16, is made up of three parts, the distribution of free electrons in the Galaxy, the Magellanic Clouds and the intergalactic medium (IGM). The Galactic model has an extend¬ed thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic HII regions, a Galactic Center disk and seven local features including the Gum Nebula, Galactic Loop I and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are with¬in the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are esti¬mated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs. It’s long been known that Sun is offset from the Galactic plane toward the North Galactic pole. We derive the Sun’s offset from the local mean Galactic plane (Z☉) using the observed z distribution of young pulsars. Pulsar distances are obtained from measurements of annual parallax, HI absorption spectra or as¬sociations where available and otherwise from the observed pulsar dispersion and a model for the distribution of free electrons in the Galaxy. We fit the cumulative distribution function for a sech2(z) distribution function, representing an isother¬mal self-gravitating disk, with uncertainties being estimated using the bootstrap method. We take young pulsars located within 4.5 kpc of the Sun, omitting those within the local spiral arm and those significantly affected by the Galactic warp, and solve for Z☉ and the scale height of the pulsar distribution, H, for differ¬ent cutoffs in pulsar characteristic age TC. We compute these quantities using just the independently determined distances, and these together with DM-based distances separately using the YMW16 and NE2001 Galactic electron density models. We find that an age cutoff at 105.75 yr with YMW16 DM-distances gives the best results with a minimum uncertainty in Z☉ and an asymptotically stable value for H. From this sample of 115 pulsars, we obtain Z☉= 13.4±4.4pc and H = 56.9±6.5 pc, similar to estimated scale heights for OB stars and open clus¬ters. Consistent results are obtained using the independent-only distances and using the NE2001 model for the DM-based distances.
Language中文
Document Type学位论文
Identifierhttp://ir.xao.ac.cn/handle/45760611-7/1703
Collection研究生学位论文
射电天文研究室
Affiliation中国科学院新疆天文台
Recommended Citation
GB/T 7714
姚菊枚. 脉冲星和快速射电暴距离模型及太阳偏离银盘距离的研究[D]. 北京. 中国科学院大学,2017.
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