首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 726 毫秒
1.
利用南山基地25 m射电望远镜在1.54 GHz频段对脉冲星PSRJ0034-0721强单个脉冲进行了观测.使用单脉冲探测方法,从1 h观测数据中探测到116个信噪比R_(SN)N≥5的单个脉冲信号.在1.54 GHz频段探测到的单个脉冲R_(SN)从5到10.5,峰值流量约是平均脉冲峰值流量的14～29倍,远小于典型巨脉冲强度与其平均脉冲强度的比.这些脉冲的强度累积分布基本符合幂律谱,拟合得到谱指数α=-4.3±0.4.本次观测对R_(SN)≥5的单个脉冲探测率为3%,对R_(SN)≥10的单个脉冲探测率约为0.08%.这些脉冲的半峰线宽(W_(50))从1.6到8 ms,平均为3.9 ms.探测到的绝大多数强单脉冲发射相位集中分布在平均脉冲轮廓的峰值相位处,但也探测到两个R_(SN)8.5的强脉冲相位提前平均脉冲轮廓峰值相位33 ms左右,表明强脉冲发射区可能有两个,符合前人在40 MHz和111 MHz频段的观测结果,但1.54 GHz频段的平均脉冲轮廓只显示一个成份.  相似文献   

2.
利用中国科学院新疆天文台南山观测站26m射电望远镜, 在中心频率1556MHz, 对Crab脉冲星(PSR B0531+21)进行了长达12.6h的连续观测, 观测带宽为512MHz, 时间分辨率为32μs, 研究了巨脉冲辐射的等待时间分布特征. 观测共探测到2097个信噪比大于10的巨脉冲, 对应的流量密度大于100Jy. 巨脉冲的爆发率表现为高度的间歇性, 在较短的时间内具有较高的爆发率, 在相对长的宁静期内巨脉冲的爆发率较低, 尤其是中间脉冲相位内的巨脉冲爆发. 相邻两个巨脉冲的等待时间分布表现为幂律分布特征, 可以用一个非稳态的泊松过程进行模拟, 这表明巨脉冲的爆发是一种独立的随机事件. 此外, 主脉冲和中间脉冲相位上的巨脉冲具有不同的等待时间分布特征, 这意味着脉冲星不同磁极的巨脉冲辐射机制可能是不同的. 这些观测结果对于理解脉冲星的射电辐射机制具有重要意义.  相似文献   

3.
受大量射频干扰信号影响,快速从海量观测数据中准确识别出单脉冲信号已成为天文数据处理的一项重要任务,而设计和提取有效数据特征,是利用机器学习进行单脉冲信号高效识别的决定因素.针对如何选择最优特征,进而提升单脉冲信号的分类精度这一关键问题,设计了面向单脉冲信号分类的集成特征选择方法.方法首先混合单脉冲信号的参数特征、统计特征和抽象特征,然后分别利用5种单一特征选择方法选出各自的最优特征集,最后利用贪心策略对5种单一方法获取的最优特征集进行集成筛选,获取最优集成特征集.实验表明,最优特征集合既包含统计特征也包含抽象特征.在相同特征数量下,利用集成特征选择比单一特征选择能获得更高的模型精度,可使F1值最高提升1.8%.在海量数据背景下,集成特征选择对减少特征数量、提升分类性能和加快数据处理速度具有重要作用.  相似文献   

4.
受大量射频干扰信号影响, 快速从海量观测数据中准确识别出单脉冲信号已成为天文数据处理的一项重要任务, 而设计和提取有效数据特征, 是利用机器学习进行单脉冲信号高效识别的决定因素. 针对如何选择最优特征, 进而提升单脉冲信号的分类精度这一关键问题, 设计了面向单脉冲信号分类的集成特征选择方法. 方法首先混合单脉冲信号的参数特征、统计特征和抽象特征, 然后分别利用5种单一特征选择方法选出各自的最优特征集, 最后利用贪心策略对5种单一方法获取的最优特征集进行集成筛选, 获取最优集成特征集. 实验表明, 最优特征集合既包含统计特征也包含抽象特征. 在相同特征数量下, 利用集成特征选择比单一特征选择能获得更高的模型精度, 可使F1值最高提升1.8%. 在海量数据背景下, 集成特征选择对减少特征数量、提升分类性能和加快数据处理速度具有重要作用.  相似文献   

5.
随着快速射电暴(Fast Radio Burst, FRB)及旋转射电暂现源(Rotating Radio Transient, RRAT)等一些没有明显周期的天体被发现以来,单脉冲搜索受到研究人员广泛关注。同时随着射电望远镜设备日趋完善,更高分辨率和更广阔的观测空间产生的观测数据量剧增,观测数据的快速处理迫在眉睫。介绍了PRESTO(PulsaR Exploration and Search TOolkit)中单脉冲搜索,使用Cython编程方式对单脉冲搜索中去趋势(Detrend)算法进行优化,并通过Ray框架实现单脉冲搜索在中央处理器(Central Processing Units, CPU)上并行化。实验结果表明,算法优化后的单脉冲搜索并行化,能明显提升搜索程序性能,显著缩短数据处理时间,同时该并行策略仅基于中央处理器,无需修改代码即可在纯中央处理器环境下实现高性能数据处理。  相似文献   

6.
利用新疆天文台25 m射电望远镜2003—2009年对PSR B0329+54长达453 h的观测数据,研究了这颗源在1540 MHz上正常模式和反常模式的轮廓稳定性时标.通过不同时间的积分脉冲轮廓与参考轮廓交叉相关系数分析,发现随积分时间的增加,两种模式的轮廓先是以较快的速度趋于稳定,在积分时间增加到约(4±1) min时,轮廓趋稳速率放缓,当积分时间达到(140±60) min (正常模式)或达到(65±15) min (反常模式)时,轮廓趋稳速度再次变快.相关系数的结果显示两种模式的轮廓在绝大多数积分时标上都不是完全随机的涨落.如果以发生轮廓趋稳速率从快到慢转变所需的积分时间作为轮廓稳定时标的判据,两种模式的稳定时标均大约为5 min.轮廓中不同成分强度比例的涨落随积分时间的变化关系各不相同,由此可以推断3个成分强度涨落性质有差异.造成轮廓趋稳行为在不同时标上有明显差异的原因有观测噪声和星际闪烁等.  相似文献   

7.
单脉冲搜索作为脉冲星探测的有力工具,在探测旋转射电暂现源以及快速射电暴中扮演着重要角色。为了从海量的射电巡天数据中快速筛选出最有价值的单脉冲搜索候选体,候选体识别已经从早期启发式阈值判断发展到基于机器学习自动识别。对于FAST观测,研究了基于机器学习的单脉冲搜索候选体识别应用到CRAFTS (the commensal radio astronomy FAST survey)超宽带脉冲星数据的性能表现。在评估过程中,使用单脉冲事件组识别(SPEGID)和单脉冲搜索器(SPS)两类自动识别方法,通过7种不同机器学习分类器对CRAFTS基准数据集产生的单脉冲搜索候选体进行自动识别;作为对比,也使用了启发式阈值判断的方法 (RRATtrap和Clusterrank)。结果表明,SPEGID具有最好的性能表现(最高的F1-score值95.1%、次高的召回率95.4%、最低的假阳性率4.7%),SPS具有最快的筛选速度(平均每小时筛选4 010个候选体)。通过对比分析结果,探讨了如何基于FAST观测数据开展高效的单脉冲搜索候选体识别。  相似文献   

8.
基于泊松模型的X射线脉冲星信号的最大似然TOA估计   总被引：1，自引：0，他引：1  
讨论了X射线脉冲星光子到达的周期平稳Poisson模型和到达时刻(Time of arrival,TOA)估计问题.在此基础上,得到了脉冲到达时刻的最大似然估计和克拉美-罗限(Cramer-Rao boundary,CRB),并推导了低信噪比情况下的似然函数近似表达和克拉美-罗限.利用解析的脉冲轮廓,对PSR B1821-24的TOA估计进行了Monte Carlo仿真,讨论了不同观测时间和信噪比下的估计误差,给出了相应的信噪比门限.研究表明:该分析方法能够有效估计X射线脉冲星的TOA定时精度,有利于评估其在各种应用中的性能.  相似文献   

9.
讨论了产生脉冲星标准脉冲轮廓的重要性.在分析经典脉冲轮廓生成方法的基础上,提出了基于小波模极大值相关处理的脉冲轮廓累加方法.首先将观测数据按周期分组,分别进行小波分解,生成粗尺度上以脉峰为特征点的小波系数;然后,选择某组高信噪比信号的系数为参考数据,分别与其它各组变换系数进行相关,确定脉峰的相对时延.最后,对分组的原始观测数据按此相对时延量进行累加,生成脉冲轮廓.观测信号可先通过背景噪声估计和平滑处理而得到信噪比较高的归一化标准轮廓.实例分析以及与模板相关法的比较结果表明:该方法简单而有效,不需要设计近似模板,且对噪声类型不敏感,具有较高的工程应用价值.  相似文献   

10.
脉冲星周期和周期变率的测量中存在着日月岁差效应.通过对日月岁差效应的分析,发现它已经影响到了某些脉冲星的周期的精密测量.在对1771颗脉冲星测量周期的分析和检测中,有81颗脉冲星的测量周期在它们的测量精度范围内受到日月岁差效应的影响.随着观测精度的提高,在以后的脉冲星周期和周期变率的精密测量中,这些影响应该得到相应的改正.  相似文献   

11.
Shemar & Lyne have previously presented observations and an analysis of 32 glitches and their subsequent relaxations observed in a total of 15 pulsars. These data are brought together in this paper with those published by other authors. We show quantitatively how glitch activity decreases linearly with decreasing rate of slow-down. As indicated previously from studies of the Vela pulsar, the analysis suggests that 1.7 per cent of the moment of inertia of a typical neutron star is normally contained in pinned superfluid which releases its excess angular momentum at the time of a glitch. There is a broad range of glitch amplitude and there is a strong indication that pulsars with large magnetic fields suffer many small glitches while others show a smaller number of large glitches. Transient effects following glitches are very marked in young pulsars and decrease linearly with decreasing rate of slow-down, suggesting that the amount of loosely pinned superfluid decreases with age. We suggest that the low braking index of the Vela and Crab pulsars cannot be caused by a decreasing moment of inertia and should be attributed to step increases in the effective magnetic moment of the neutron star at the glitches.  相似文献   

12.
We present a simple method for determination of the orbital parameters of binary pulsars, using data on the pulsar period at multiple observing epochs. This method uses the circular nature of the velocity space orbit of Keplerian motion and produces preliminary values based on two one-dimensional searches. Preliminary orbital parameter values are then refined using a computationally efficient linear least-squares fit. This method works for random and sparse sampling of the binary orbit. We demonstrate the technique on (i) the highly eccentric binary pulsar PSR J0514−4002 (the first known pulsar in the globular cluster NGC 1851) and (ii) 47 Tuc T, a binary pulsar with a nearly circular orbit.  相似文献   

13.
We present polarization profiles at 1.4 and 3.1 GHz for 14 young pulsars with characteristic ages less than 75 kyr. Careful calibration ensures that the absolute position angle of the linearly polarized radiation at the pulsar is obtained. In combination with previously published data, we draw three main conclusions about the pulse profiles of young pulsars. (i) Pulse profiles are simple and consist of either one or two prominent components. (ii) The linearly polarized fraction is nearly always in excess of 70 per cent. (iii) In profiles with two components, the trailing component nearly always dominates, only the trailing component shows circular polarization and the position angle swing is generally flat across the leading component and steep across the trailing component.
Based on these results, we can make the following generalizations about the emission beams of young pulsars. (i) There is a single, relatively wide cone of emission from near the last open field lines. (ii) Core emission is absent or rather weak. (iii) The height of the emission is between 1 and 10 per cent of the light cylinder radius.  相似文献   

14.
The analysis of observations of pulsar B1931+24 shows that the mechanism of the spin-down of a rotating magnetized neutron star is due to the plasma generation in its magnetosphere and, consequently, the radio emission generation. The unique observation of the switch on and switch off of this pulsar allows us to distinguish between the energy loss in the absence of radio emission (the magnetodipole radiation) and the current loss due to the rotation energy expenditure to the relativistic plasma generation and acceleration in the pulsar magnetosphere. The inclination angle χ, the angle between the rotation axis and the magnetic dipole axis, can be stationary for this pulsar,  χ=χst  . From observations and theory it follows that  χst= 59°  .  相似文献   

15.
Motivated by recent results on the location of the radio emission in pulsar magnetospheres, we have developed a model which can account for the large diversity found in the average profile shapes of pulsars. At the centre of our model lies the idea that radio emission at a particular frequency arises from a wide range of altitudes above the surface of the star, and that it is confined to a region close to the last open field lines. We assert that the radial height range over which emission occurs is responsible for the complex average pulse shapes rather than the transverse (longitudinal) range proposed in most current models. By implementing an abrupt change in the height range to discriminate between young, short-period, highly energetic pulsars and their older counterparts, we obtain the observed transition between the simple and complex average pulse profiles observed in each group respectively. Monte Carlo simulations are used to demonstrate the match of our model to real observations.  相似文献   

16.
We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane  (45° < l < 135°; | b | < 1°)  with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The survey covered 106 deg2 with a sensitivity of roughly 1 mJy to long-period pulsars (pulsars with period longer than 1 s). The three new pulsars have periods of 318, 933 and 1056 ms. Their timing parameters and flux densities, obtained in follow-up observations with the Lovell Telescope at Jodrell Bank and the GMRT, are presented. We also report on pulse nulling behaviour in one of the newly discovered pulsars, PSR J2208+5500.  相似文献   

17.
We present the results of a 430-MHz survey for pulsars conducted during the upgrade to the 305-m Arecibo radio telescope. Our survey covered a total of 1147 deg2 of sky using a drift-scan technique. We detected 33 pulsars, 10 of which were not known prior to the survey observations. The highlight of the new discoveries is PSR J0407+1607, which has a spin period of 25.7 ms, a characteristic age of 1.5 Gyr and is in a 1.8-yr orbit about a low-mass  (>0.2 M⊙)  companion. The long orbital period and small eccentricity  ( e = 0.0009)  make the binary system an important new addition to the ensemble of binary pulsars suitable to test for violations of the strong equivalence principle. We also report on our initially unsuccessful attempts to detect optically the companion to J0407+1607, which imply that its absolute visual magnitude is >12.1. If, as expected on evolutionary grounds, the companion is an He white dwarf, our non-detection implies a cooling age of least 1 Gyr.  相似文献   

18.
We have detected the rare phenomenon of stable, drifting sub-pulse behaviour in two pulsars discovered in the recent Swinburne intermediate latitude pulsar survey. The pulsars, PSR     and PSR J1919+0134, have approximate periods ( P ) of 1.873 and 1.6039 s respectively.
Both pulsars have multicomponent profiles, and distinct drifting is observed across them. We have identified a single drift mode in both pulsars: the drift rate for PSR     being 5.4(1) ms P −1 and 5.8(2) ms P −1 for PSR 1919+0134. The drifting is linear across the profile with no departure from linearity at the edges within the sensitivity of our observations.  相似文献   

19.
A luminosity law for radio pulsars was proposed by Stollman, based on features of the RudermanSutherland model. We analyse that proposition in the light of the most recent data (the catalogue of Taylor, Manchester & Lyne), and perform a set of statistical tests to verify the reliability of the results. We find little evidence favouring Stollman's law, and point out a possible incompleteness of the data sets, without conclusive evidence for or against the RudermanSutherland model.  相似文献   

20.
The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号