利用费米卫星大面积望远镜对脉冲星的观测研究

费米γ射线空间望远镜(Fermi)自2008年8月观测任务开始以来,以其优越的观测性能开启了γ射线天文学研究的新纪元。其搭载的大面积望远镜(LAT)在脉冲星探测和研究方面取得了巨大的成功。除了探测到已知脉冲星的γ射线脉冲辐射信号外,LAT还能够利用γ射线数据的盲寻技术独立发现脉冲星,此外还提供了大量γ射线源进行射电脉冲搜寻。Fermi-LAT的观测带来了γ射线脉冲星数量的显著增长,确立了脉冲星是银河系内主要的γ射线源,并且探测到了毫秒脉冲星的γ射线辐射。一般来说,在长时标下脉冲星的γ射线辐射流量稳定且脉冲形状多呈现双峰结构,能谱可由具有指数截断的幂律谱描述。综述了利用Fermi-LAT数据寻找脉冲辐射信号的方法和研究γ射线脉冲星所得到的主要结果,并简要介绍了近年来在脉冲星研究方面取得的新成果。     

Background simulations for the Large Area Detector onboard LOFT

The Large Observatory For X-ray Timing (LOFT), currently in an assessment phase in the framework the ESA M3 Cosmic Vision programme, is an innovative medium-class mission specifically designed to answer fundamental questions about the behaviour of matter, in the very strong gravitational and magnetic fields around compact objects and in supranuclear density conditions. Having an effective area of ～10 m² at 8 keV, LOFT will be able to measure with high sensitivity very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and optimize the design of its main instrument, the Large Area Detector (LAD). In this paper the results of an extensive Geant-4 simulation of the instrumentwillbe discussed, showing the main contributions to the background and the design solutions for its reduction and control. Our results show that the current LOFT/LAD design is expected to meet its scientific requirement of a background rate equivalent to 10 mCrab in 2?30 keV, achieving about 5 mCrab in the most important 2–10 keV energy band. Moreover, simulations show an anticipated modulation of the background rate as small as 10 % over the orbital timescale. The intrinsic photonic origin of the largest background component also allows for an efficient modelling, supported by an in-flight active monitoring, allowing to predict systematic residuals significantly better than the requirement of 1 %, and actually meeting the 0.25 % science goal.     

Pulsar timing observations with Haoping Radio Telescope

We report pulsar timing observations carried out in L-band with NTSC's 40-meter Haoping Radio Telescope(HRT), which was constructed in 2014. These observations were carried out using the pulsar machine we developed. Timing observations toward millisecond pulsar J0437–4715 obtain a timing residual(r.m.s.) of 397 ns in the time span of 284 days. Our observations successfully detected Crab pulsar's glitch that happened on 2019 July 23.     

A tool to estimate the Fermi Large Area Telescope background for short-duration observations

The proper estimation of the background is a crucial component of data analyses in astrophysics, such as source detection, temporal studies, spectroscopy, and localization. For the case of the Large Area Telescope (LAT) on board the Fermi spacecraft, approaches to estimate the background for short (≲1000 s duration) observations fail if they ignore the strong dependence of the LAT background on the continuously changing observational conditions. We present a (to be) publicly available background-estimation tool created and used by the LAT Collaboration in several analyses of Gamma Ray Bursts. This tool can accurately estimate the expected LAT background for any observational conditions, including, for example, observations with rapid variations of the Fermi spacecraft’s orientation occurring during automatic repointings.     

甚大面积伽马射线空间望远镜计划

高能伽马射线探测是研究极端天体物理的主要途径之一.空间高能伽马射线探测具有覆盖波段宽、时间连续性好、能量分辨率高等突出优势.在成功研发并运行我国首颗天文卫星—“悟空”号(DArk Matter Particle Explorer, DAMPE)的基础上,紫金山天文台联合国内的多家单位提议研制甚大面积伽马射线空间望远镜(Very Large Area gamma-ray Space Telescope, VLAST),该望远镜在GeV–TeV能段接受度高达10 m2·sr,并具有强的MeV–GeV波段探测能力,其综合性能预期比费米卫星的大面积伽马望远镜(Fermi-LAT (Large Area Telescope))提升10倍之上.重点介绍了VLAST的主要科学目标,探测器的初步配置及预期性能指标.     

Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST)

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Pulsar observations at 34.5 MHz using the Gauribidanur Telescope: I

The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term variations in the pulsar signals at this low frequency.     

空间硬X射线望远镜HAPI-1及其对蟹状星云脉冲星的观测

HAPI-1是我国第一个用于空间高能天文观测的硬X射线望远镜系统,由面积145cm~2厚0.5cm的CsI(T1)主探测晶体及其下部厚5cm的NaI(T1)反符合晶体构成复合晶体探测器,采用脉冲形状甄别技术区分两种晶体的输出信号,多种物质构成的夹层式屏蔽筒和准直器使望远镜具有约4°视场角(HWHM),电子学、姿态控制和数据获取系统使望远镜具有对20—200keV能区高能光子到达时刻和能量进行空间定向观测的能力。本文介绍HAPI-1的构成和主要性能,以及1984年5月利用该望远镜在我国高空科学气球上对蟹状星云脉冲星的观测结果。     

In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope

The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth’s magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∼6 and ∼13 GeV with an estimated uncertainty of ∼2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.     

A Large Glitch in the Crab Pulsar

1 INTRODUCTIONA pulsar glitch is a phenomenon in which the pulse frequency has a sudden increase, typicallywith a fractional ~litude an/u in the range of 10--8 -- 10--6. Glitches are Unpredictable butoccur at intervals of a few y6ars in many young pulsars. Coincident with the glitch, there is oftenan increajse in the magnitude of the frequency derivative followed by thlee types of recovery:almost no recoveryt partial recovery and total recovery on timescales from days to years. It isbelie…     

乌鲁木齐天文站25m天线18cm脉冲星脉冲到达时间观测系统

脉冲星脉冲到达时间观测系统建立在２５ｍ射电天线的１８ｃｍ波段上,消色散采用了２ｘ１２８ｘ２．５ＭＨｚ多通过滤波器和数字化器,数据采集系统由ＰＣ机完成．１９９９年５月至６月间建立了基于常温接收机的到达时间观测系统．观测到的最弱源的平均流量密度为４ｍＪｙ．     

Interferometry with the Large Binocular Telescope

The Large Binocular Telescope (LBT) will be the largest single telescope in the world when it is completed in 2005. The unique structure of the telescope incorporates two, 8.4 meter diameter primary mirrors on a 14.4 meter center-to-center mounting. This configuration provides the equivalent collecting area of a 12 meter telescope, and when combined coherently, the two optical paths offer very interesting possibilities for interferometry. Two initial interferometric instruments are planned for the LBT. A group based at the University of Arizona is constructing LBTI, a pupil-plane, nulling beam combiner operating in the thermal infrared N band. This instrument will search for and measure zodiacal light in candidate stellar systems for the Terrestrial Planet Finder (TPF) and Darwin missions. Expansion ports can accomodate additional instruments. A second group, based in Heidelberg, Arcetri, and Köln, is building LINC-NIRVANA, a near-infrared Fizeau-mode beam combiner. This type of observation preserves phase information and allows true imagery over a wide field of view. Using state-of-the-art detector arrays, coupled with advanced adaptive optics, LINC-NIRVANA will deliver the sensitivity of a 12 m telescope and the spatial resolution of a 23 m telescope, over a field of view up to 2 arc minutes square.     

Next Generation Instrumentation for the Very Large Telescope Interferometer

The scientific capabilities of the VLT Interferometer can be substantially enhanced through new focal-plane instruments. Many interferometric techniques– astrometry, phase-referenced imaging, nulling, and differential phase measurements – require control of the phase to ≲ 1 rad; this capability will be provided at the VLTI by the PRIMA facility. Phase-coherent operation of the VLTI will also make it possible to perform interferometry with spectral resolution up to R ∼ 100,000 by building fiber links to the high-resolution spectrographs UVES and CRIRES. These developments will open new approaches to fundamental problems in fields as diverse as extra solar planets,stellar atmospheres, circumstellar matter, and active galactic nuclei. This revised version was published online in July 2006 with corrections to the Cover Date.     

Longitudinal dispersion compensation for the Very Large Telescope Interferometer

The Very Large Telescope Interferometer [1,13] will be operated in air which will introduce small optical path fluctuations due to internal turbulence [4,6] and dispersion effects. Both may contribute to fringe contrast decrease. Longitudinal dispersion effects can be corrected by inserting an appropriate glass of variable thickness in one arm of the interferometer [3,5,11,12]. This paper presents a new method applied to VLTI in order to select the optimum glass, according to both the observing wavelength and the spectral bandpath, and to calculate its thickness. Results are presented in terms of improvement on the fringe contrast.     

Site testing campaign for the Large Optical/infrared Telescope of China:overview

The Large Optical/infrared Telescope(LOT) is a ground-based 12 m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade.Based on satellite remote sensing data,along with geographical,logistical and political considerations,three candidate sites were chosen for ground-based astronomical performance monitoring.These sites include:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.Up until now,all three sites have continuously collected data for two years.In this paper,we will introduce this site testing campaign,and present its monitoring results obtained during the period between March 2017 and March 2019.     

Preface:Site testing campaign for the Large Optical/infrared Telescope of China

The Large Optical/infrared Telescope of China is a 12 meter diameter ground-based optical/infrared telescope which is proposed to be constructed in the western part of China in favor of its arid climate,and clear,dark nights.A site testing campaign was initiated between November 2016 and March2019 in order to investigate long term astronomical weather conditions in the western part of China,specifically,at three sites:Ali in Tibet,Daocheng in Sichuan and Muztagh-ata in Xinjiang.This is the first attempt to evaluate long term performances of three candidate sites with uniformly calibrated instruments and data collecting/processing methods for a two-year span in China.In this special issue,we present nine papers that describe the whole site testing campaign,including preparation,data collecting/processing methods,instrument set up at three candidate sites as well as detailed statistics for the measurement results from March 2017 to March 2019.     

大天区面积多目标光纤光谱望远镜(LAMOST)的跟踪运动

大天区面积多目标光纤光谱望远镜（ＬＡＭＯＳＴ），是一架反射Ｓｃｈｍｉｄｔ望远镜．它固定地斜卧在地面上，主光轴在子午面内南端高起与地面成２５°角．观测天区－１０°δ＋９０°，天体经过子午圈前后观测１．５小时．有三种跟踪运动：改正板在地平式机架上绕高度轴和方位轴的转动以及焦面的转动．这些运动都没有盲区．本文导出了全部角位移、角速度和角加速度的公式．对上述天区和观测时间作了计算，高度角的最大变化仅０．３４°，重力变化引起的变形极小，改正板方位角和焦面的转动速度小于或等于周日运动速度，且转动相当均匀．发现并证明了当中心天体的赤纬δ＝９０°－－Ａ＝＋２４．６°（Ａ为光轴倾角，为观测点的地理纬度）时，焦面的转动恒等于零．这些研究表明ＬＡＭＯＳＴ的装置在跟踪运动和重力变形方面有一系列重要的优点．     

The UK Large Telescope project

The current status and the organization of the UK Large Telescope programme are summarized. Some scientific and design issues are discussed on the basis of work done for the SERC Large Telescope Panel report. A national Phase A programme is now underway addressing more detailed aspects of these questions. This study will culminate in a final proposal for funding in 1990.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

上海天文台25 m射电望远镜首次单天线脉冲星观测

介绍上海天文台25 m射电望远镜首次单天线脉冲星观测。2010年4月23日,使用上海天文台位于佘山观测基地的25 m射电望远镜对脉冲星J0332+5434在L波段进行了观测,此次观测使用VLBI终端进行数据采集记录,通过对观测数据进行非相干消色散和周期折叠,成功获得目标源的平均轮廓。此次观测的成功,表明该天线具备开展单天线脉冲星观测的条件,并为上海天文台建设中的65 m天线的天文观测提供了参考,为将来自主研发脉冲星终端进行了技术储备。