射电望远镜多目标观测策略优化

望远镜调度是望远镜运行中的关键组成部分, 用于辅助科研人员进行合理的观测计划安排, 提高望远镜的运行效率, 获取高质量的观测数据. 然而, 由于不同观测项目的科学需求不同, 望远镜的调度过程十分复杂. 针对短周期多目标的观测项目, 考虑望远镜换源时转动时长、观测高度角等因素进行建模, 采用贪心算法对中国科学院新疆天文台南山26m望远镜脉冲星到达时间观测列表进行调度. 通过模拟表明, 使用算法完成的观测列表可以有效地减少观测过程中的平均转动时长, 提升观测数据的质量, 提高望远镜时间利用率, 减少科研人员对观测列表编排的负担.     

Scintillation Observations of Strong Northern Pulsars

Scintillation of pulsar radio emission provides information about the interstellar medium along the path to the pulsar and the velocities of pulsars. It also affects the precision of pulse timing observations. Using a pulsar timing system developed at the Urumqi Astronomical Observatory25 m telescope, we observed diffractive scintillation dynamic spectra for several strong northern pulsars. This paper introduces the observing system and discusses the observational results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long-term scintillation observations of five pulsars at 1540 MHz

From 2001 January to 2002 June, we monitored PSRs B0329+54, B0823+26, B1929+10, B2020+28 and B2021+51 using the Nanshan 25-m radio telescope of the Urumqi Observatory to study their diffractive interstellar scintillation (DISS). The average interval between observations was about 9 d and the observation duration ranged between 2 and 6 h depending on the pulsar. Wide variations in the DISS parameters were observed over the 18-month data span. Despite this, the average scintillation velocities are in excellent agreement with the proper motion velocities. The average two-dimensional autocorrelation function for PSR B0329+54 is well described by a thin-screen Kolmogorov model, at least along the time and frequency axes. Observed modulation indices for the DISS time-scale and bandwidth and the pulsar flux density are greater than values predicted for a Kolmogorov spectrum of electron density fluctuations. Correlated variations over times that are long compared to the nominal refractive scintillation time are observed, suggesting that larger scale density fluctuations are important. For these pulsars, the scintillation bandwidth as a function of frequency has a power-law index  (∼3.6)  much less than that expected for Kolmogorov turbulence (∼4.4). Sloping fringes are commonly observed in the dynamic spectra, especially for PSR B0329+54. The detected range of fringe slopes are limited by our observing resolution. Our observations are sensitive to larger-scale fringes and hence smaller refractive angles, corresponding to the central part of the scattering disc.     

用50m射电望远镜作脉冲星观测与研究

国家天文台正在研制的50m射电望远镜将投入脉冲星观测与研究，推动我国的脉冲星工作。本文回顾了自第1颗脉冲星发现后35年来脉冲星观测取得的成果，和理论研究获得的重大进展，并讨论我国脉冲星工作可能开展的观测与研究。当今世界脉冲星观测与研究虽然还有许多遗留问题，但是作为中子星基本观测事实已被确认。脉冲星的应用也已经走上了历史舞台。如果利用50m射电望远镜对脉冲星的特殊活动现象进行观测与研究，可能获得突破性的进展。     

脉冲星时间特征和多星计时观测

在评介脉冲星时研究发展趋势的基础上,讨论了基于毫秒脉冲星自转的脉冲星时间的短期特征和长期稳定度,并对影响其稳定度的因素作了初步分析.50m射电望远镜计时观测的目的之一就是综合脉冲星时研究.对于50m望远镜计时观测的选星和由多星观测进行综合脉冲星时研究中的数据分析问题进行了讨论.     

乌鲁木齐天文站脉冲星观测研究新进展

乌鲁木齐天文站自 1 999年研制完成 1 .5GHz频段室温双偏振消色散接收系统。 2 0 0 2年又完成 1 .5GHz频段致冷式双偏振消色散接收系统。我们成功地完成了第一个国际合作协议的任务。为在我国建立高灵敏度的观测脉冲星设备和取得优秀的脉冲星观测结果作出了贡献。为了进一步发展乌站脉冲星观测 ,第二个合作协议包括利用致冷式系统进行脉冲星大样本的监测和建立低频段的基带技术的消色散系统。     

Scintillation parameters for 49 pulsars

We report on multi-epoch, multifrequency observations of 64 pulsars with high spectral and time resolution. Scintillation parameters were obtained for 49 pulsars, including 13 millisecond pulsars. Scintillation speeds were derived for all 49, which doubles the number of pulsars with speeds measured in this way. There is excellent agreement between the scintillation speed and proper motion for the millisecond pulsars in our sample using the simple assumption of a mid-placed scattering screen. This indicates that the scaleheight of scattering electrons is similar to that of the dispersing electrons. In addition, we present observations of the Vela pulsar at 14 and 23 GHz, and show that the scintillation bandwidth scales as ν^3.93 over a factor of 100 in observing frequency. We show that for PSR J0742−2822, and perhaps PSR J0837−4135, the Gum nebula is responsible for the high level of turbulence along their lines of sight, contrary to previous indications. There is a significant correlation between the scintillation speeds and the product of the pulsar's period and period derivative for the 'normal' pulsars. However, we believe this to be caused by selection effects both in pulsar detection experiments and in the choice of pulsars used in scintillation studies.     

Flux density measurements for 32 pulsars in the 20 cm observing band

Flux densities are fundamental observational parameters that describe a pulsar. In the current pulsar catalogue, 27% of the listed radio pulsars have no flux density measurement in the 20 cm observing band. Here, we present the first such measurements for 32 pulsars observed employing the Parkes radio telescope. We have used both archival and new observations to make these measurements. Various schemes exist for measuring flux densities and we show how the measured flux densities vary between these methods and how the presence of radio-frequency interference will bias the flux density measurements.     

A search for compact decametric radio sources in supernova remnants using the interplanetary scintillation technique

Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial.     

国家授时中心40米射电望远镜Crab脉冲星周期跃变监测

脉冲星周期跃变是一种罕见的现象,是研究其内部结构的探针。针对2019年2月~12月国家授时中心昊平观测站40 m射电望远镜在脉冲星计时观测中监测Crab脉冲星的数据,采用脉冲星计时方法,用TEMPO2拟合程序进行分析。结果表明,Crab脉冲星在2019年7月23日(MJD 58687)附近发生了一次周期跃变现象,该跃变自转增量为Δv_g=5.33(4)×10^-7Hz,自转变化量为Δv_g/v=17.9(1)×10^-9,并伴随着恢复系数Q~0.88的指数恢复过程。此次Crab脉冲星周期跃变的监测及处理,证实了40 m射电望远镜对脉冲星的监测性能,同时为研究周期跃变的产生机理积累了样本。     

Polarization observations of giant radio pulses from the millisecond pulsar B1937+21 at a frequency of 600 MHz

We performed polarization observations of giant radio pulses from the millisecond pulsar B1937+21. The observations were carried out in July 2002 with the 64-m Kalyazin radio telescope at a frequency of 600 MHz in two polarization channels with left-and right-hand circular polarizations (RCP and LCP). We used the S2 data acquisition system with a time resolution of 125 ns. The duration of an observing session was 20 min. We detected twelve giant radio pulses with peak flux densities higher than 1000 Jy; five and seven of these pulses appeared in the RCP and LCP channels, respectively. We found no event that exceeded the established detection threshold simultaneously in the two polarization channels. Thus, we may conclude that the detected giant pulses have a high degree of circular polarization, with the frequency of occurrence of RCP and LCP pulses being the same.     

New Features of the Pulsar B0950+08 Radiation at the Frequency of 111 MHz

Results of long time observations of the pulsar B0950+08 are given.These observations were carried out at the LPA radio telescope at the frequency of 111 MHz fr...     

Spatial modulation search applied to the search and confirmation of highly scintillated pulsars at FAST with a pulsar discovered in M3

We present a pulsar candidate identification and confirmation procedure based on a position-switch mode during the pulsar search observations. This method enables the simultaneous search and confirmation of a pulsar in a single observation, by utilizing the different spatial features of a pulsar signal and radio frequency interference(RFI). Based on this method, we performed test pulsar search observations in globular clusters M3, M15 and M92. We discovered and confirmed a new pulsar, M3 F, and detected the known pulsars M3 B, M15 A to G(except C) and M92 A.     

脉冲星VLBI观测软件相关处理进展

VLBI是进行高分辨率脉冲星观测研究的重要手段.脉冲星信号是非常微弱的脉冲序列,其VLBI观测面临多种挑战.在数据相关过程中采用有效技术提取脉冲星信号可提高观测成功率和精度.DiFX(Distributed FX-style Software Correlator)是目前国际上流行的开源软件相关处理机,它采用非相干消色散技术和“脉冲星数据分箱技术”(Pulsar Binning),在脉冲星VLBI观测数据的相关处理方面具有优异的性能.介绍了DiFX的构架,安装、调试方法,并对利用DiFX处理脉冲星VLBI观测数据的进展情况进行论述.利用单机环境下的DiFX,在普通模式和Pulsar Binning模式下对中国VLBI网(CVN)第一次脉冲星观测数据进行相关处理;利用德国马普射电天文研究所集群计算环境下的Bonn-DiFX,在Pulsar Binning模式下对流量仅有2.6 mJy的毫秒脉冲星PSRJ1022+1001的欧洲VLBI网(EVN)观测数据成功进行相关处理.最后,对使用DiFX处理脉冲星观测数据情况进行总结,并展望了今后CVN开展脉冲星观测研究的前景.     

云南天文台40米射电望远镜河外射电源观测

为了在云南天文台40 m天线上开展射电天文研究,使用它进行了河外射电源流量试观测。通过对河外致密源进行ON/OFF跟踪观测,得到射电源的流量变化曲线。但数据质量并不理想,说明系统存在一些问题。随后,根据对该望远镜系统的稳定性及其无线电环境干扰现状的考察,以及对现存问题的分析,提出了相应的解决方法。     

基于小波分析的脉冲星信号消噪处理

脉冲星信号是一种典型的非平稳信号,且信噪比非常小．目前对脉冲星信号的处理仅局限于对脉冲星信号不同周期的迭加．根据脉冲星信号的特点采用小波消噪的方法对其进行处理,并对小波的选取和分解层数的优化进行了研究．结果表明小波阈值消噪能够对脉冲星信号实现噪声剔除,达到既净化信号,又不丢失高频有用信息的目的．从而实现了迭加较少的信号周期就能够获得与较长时间迭加相似或更好的效果,可以大大提高脉冲星观测的轮廓精度．     

Towards practical autonomous deep-space navigation using X-Ray pulsar timing

We investigate the feasibility of deep-space navigation using the highly stable periodic signals from X-ray pulsars in combination with dedicated instrumentation on the spacecraft: a technique often referred to as ‘XNAV’. The results presented are based on the outputs from a study undertaken for the European Space Agency. The potential advantages of this technique include increased spacecraft autonomy and lower mission operating costs. Estimations of navigation uncertainties have been obtained using simulations of different pulsar combinations and navigation strategies. We find that the pulsar PSR B1937?+?21 has potential to allow spacecraft positioning uncertainties of ~2 and ~5 km in the direction of the pulsar after observation times of 10 and 1 h respectively, for ranges up to 30 AU. This could be achieved autonomously on the spacecraft using a focussing X-ray instrument of effective area ~50 cm² together with a high performance atomic clock. The Mercury Imaging X-ray Spectrometer (MIXS) instrument, due to be launched on the ESA/JAXA BepiColombo mission to Mercury in 2018, is an example of an instrument that may be further developed as a practical telescope for XNAV. For a manned mission to Mars, where an XNAV system could provide valuable redundancy, observations of the three pulsars PSR B1937?+?21, B1821-24 and J0437-4715 would enable a three-dimensional positioning uncertainty of ~30 km for up to 3 months without the need to contact Earth-based systems. A lower uncertainty may be achieved, for example, by use of extended observations or, if feasible, by use of a larger instrument. X-ray instrumentation suitable for use in an operational XNAV subsystem must be designed to require only modest resources, especially in terms of size, mass and power. A system with a focussing optic is required in order to reduce the sky and particle background against which the source must be measured. We examine possible options for future developments in terms of simpler, lower-cost Kirkpatrick-Baez optics. We also discuss the principal design and development challenges that must be addressed in order to realise an operational XNAV system.     

High-precision timing of PSR J1600−3053

We present the results of a high-precision timing campaign directed at the binary millisecond pulsar J1600−3053. Submicrosecond pulsar timing has long been the domain of bright, low dispersion measure millisecond pulsars or large diameter telescopes. This experiment, conducted using the Parkes radio telescope in New South Wales, Australia, and utilizing the latest baseband recording hardware, has allowed this pulsar, although distant and faint, to present residuals to a model of its spin behaviour of 650 ns over a period of more than 2 yr. We have also constrained the orbital inclination via Shapiro delay to be between 59° and 70° to 95 per cent confidence and obtained a scintillation velocity measurement indicating a transverse velocity less than 84 km s⁻¹. This pulsar is demonstrating remarkable stability comparable to, and in most cases improving upon, the very best long-term pulsar timing experiments. If this stability is maintained, the current limits on the energy density of the stochastic gravitational wave background will be reached in four more years.     

Maximum-likelihood astrometric geometry calibration of interferometric telescopes: application to the Very Small Array

Interferometers require accurate determination of the array configuration in order to produce reliable observations. A method is presented for finding the maximum-likelihood estimate of the telescope geometry, and of other instrumental parameters, astrometrically from the visibility timelines obtained from observations of celestial calibrator sources. The method copes systematically with complicated and unconventional antenna and array geometries, with electronic bandpasses that are different for each antenna radiometer, and with low signal-to-noise ratios for the calibrators. The technique automatically focuses on the geometry errors that are most significant for astronomical observation. We apply this method to observations made with the Very Small Array and constrain some 450 telescope parameters, such as the antenna positions, effective observing frequencies and correlator amplitudes and phaseshifts; this requires only ∼1 h of CPU time on a typical workstation.     

First Observations from the Multi-Application Solar Telescope (MAST) Narrow-Band Imager

The Multi-Application Solar Telescope is a 50 cm off-axis Gregorian telescope recently installed at the Udaipur Solar Observatory, India. In order to obtain near-simultaneous observations at photospheric and chromospheric heights, an imager optimized for two or more wavelengths is being integrated with the telescope. Two voltage-tuneable lithium-niobate Fabry–Perot etalons along with a set of interference blocking filters have been used for developing the imager. Both of the etalons are used in tandem for photospheric observations in Fe i 6173 Å and chromospheric observation in H\(\alpha\) 6563 Å spectral lines, whereas only one of the etalons is used for the chromospheric Ca II line at 8542 Å. The imager is also being used for spectropolarimetric observations. We discuss the characterization of the etalons at the above wavelengths, detail the integration of the imager with the telescope, and present a few sets of observations taken with the imager set-up.