Pulsar-based Time Scale National Space Science Center. CAS Ding Chen, PPTA team 2013年8月22日, 脉冲星讲习班 National Space Science Center. CAS

Outline Time Standard TAI and UTC Pulsar Time Scale algorithm simulation real data Potential Application of PT(FAST) Problem and future improvements Discussion

时间，是当今测量准确度最高的基本物理量，应用最广泛的物理量，惟一实现全球高精度传递的物理量。随着信息化、数字化时代的到来，高精度时间频率已经成为一个国家科技、经济、军事和社会生活中至关重要的参量。 基础研究领域 天文学、 物理学 地球动力学、 大地测量学 …… 工程技术领域 信息传递、电力输配、 深空探测、遥感测绘、 导航定位、武器实验、 地震监测、计量测试 …… 国家重大系统 交通运输、电力、 金融证券、 邮电通信 国防安全 …….

时间与定位导航 百万分之一秒的误差会造成 300m 的定位误差！

时间与科学研究 VLBI(Very Long Baseline Interferometry) 相对论验证：狭义相对论中指出，惯性参考系中运动的钟比静止的钟走得慢，而且钟的运动速度越快，这种效应越明显。——原子钟飞机飞行试验验证。 广义相对论中的红移理论。——星载原子钟验证。 7个基本物理量，通过时间频率重新定义。 长度——米（1983年） 电压——伏特（1990年） 电阻——欧姆（1990年）

时间物理量的特点 “时”与“间”：时刻 & 间隔 时间，是连续流逝的物理量，其测量依靠物质的连续的或周期性的运动。 时间的特质：连续性、矢向性、均匀性、稳定性。 任何一个周期性的物理过程，都可以用于计时！ 连续性：子在川上曰：逝者如斯夫，不舍昼夜。 均匀性：节拍、步调一致；准确度 稳定性：时间基准；稳定度

“ 位于海平面上的铯133原子基态两个超精细能级间在零磁场中跃迁辐射振荡 9,192,631,770 周所持续的时间为一个原子时秒。”

Log (y()) Log (), seconds 1 day 1 month The Stabilities of different Frequency Scales Log (y()) Log (), seconds -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 1 day 1 month -9 -10 -11 -12 -13 -14 -15 -16 Hydrogen Maser Rubidium Quartz Cesium

Ensemble Atomic Time Scale TAI calculation is done each month BIPM firstly computes a free atomic scale: EAL, from around 400 clocks all over the world, to get the optimal high 1-month stability. --AlGOS: weighted average algorithm. --An average of N identical clocks may be more stable than individual one clock -- Time comparison to same laboratory (PTB) of different laboratories (time transfer GPS CV) -- EAL is stable but may have some values shift to SI second. Every month, primary frequency standard (PFS) are used to estimate the TAI from the frequency correction of EAL in order to be more closer to SI second.

The weights of different Lab(k) in TAI NICT NIST USNO NTSC The weights of different Lab(k) in TAI

Time Links and Comparation

TAI and UTC: leap second Coordinated Universal Time (UTC), maintained by the BIPM, is the time scale that forms the basis for the coordinated dissemination of standard frequencies and time signals. The UTC scale is adjusted by the insertion of leap seconds to ensure approximate agreement with the time derived from the rotation of the Earth. Physical realizations of UTC – named UTC (k) – are maintained in national metrology institutes or observatories contributing with their clock data to the BIPM. The dates of leap seconds of UTC are decided and announced by the International Earth Rotation and Reference Systems Service (IERS), which is responsible for the determination of Earth rotation parameters and the maintenance of the related celestial and terrestrial reference systems.

TT(BIPM) TAI is computed in real time and will not be updated even an error is discovered, so it is not optimal. Therefore the BIPM computes a post-processed time scale TT(BIPM) Each new version TT(BIPMxx) updates and replaces the previous one. – Post-processed using all available PFS data. – Complete re-processing starting 1993 (change of algorithm). – Monthly estimation of the data are smoothed and integrated to obtain TT(BIPMxx). Significant and time-varying frequency difference between TAI and TT(BIPM) integrates to more than 100 ns/yr, so TAI should not been used as a long-term reference.

Ensemble time scale: aiming at 10-16 and beyond More clocks for time keeper, a 100-fold increase in clock number would be needed to reach 10-16 . New clock technologies: Cs, Rb fountain, Light clock :100-200 clocks, each with ≈ 5×10-15 stability @ 1 month provide 3-4×10-16 for the ensemble time scale) Long term stability (more than 3 months or one year) ~ 10-16 or beyond : Combined with a independent more stable time scale (Pulsar Time Scale is a good candidate)

Ensemble Pulsar Time Scale The arrival time of each Pulsar ‘k’ which is its date in PTK, to be actually measured based on atomic clock, which is date in TAI. So we can obtain Rk=TAI-PTk. which is the timing residuals. Ensemble Pulsar Time Scale(EPT) : PPTA is the best project to establish the new independent ensemble time scale which will take contribution to both GW detection and BIPM.

What happens if irregularities exist in time-scale What happens if irregularities exist in time-scale? TT(TAI)-TT(BIPM2010)

New Technique Define clock function to be simple Fourier expansion: (note: can use other functional forms if needed) Carry out a standard least-squares fit of pulsar timing model parameters + f(t) as usual, except: simultaneously fit to multiple pulsars use measurement of the covariance in the residuals for a given pulsar as part of the least-squares-fit fit (to deal with timing noise)

Final result (PPTA data) PT(PPTA)-TT(TAI) and TT(BIPM2010)-TT(TAI) 1ms

PT(ppta)-BIPM(2010) – time transfer? PKS->GPS->TT(TAI) PKS->TID->UTC(NIST)->TT

What the PT could do? Time Keeper for long-term scale Correction for atomic clock Combining our data with observations from Europe, USA and PPTA will allow us to make a significant improvement on our time scale Contributions to BIPM check/correct long-term timing irregularities Time transfer Improvement for GW-detection Experiment in the space orbit CSIRO. Gravitational wave detection

What the PT could do? Time Keeper for long-term scale Correction for atomic clock Combining our data with observations from Europe, USA and PPTA will allow us to make a significant improvement on our time scale Contributions to BIPM check/correct long-term timing irregularities Improvement for GW-detection Time transfer Experiment in the space orbit CSIRO. Gravitational wave detection

IPTA_clock PPTA, NANOGrav, EPTA, FAST, GTT…… Ipta_clock@lists.pulsarastronomy.net http://lists.pulsarastronomy.net/mailman/listinfo

What the PT could do? Time Keeper for long-term scale Correction for atomic clock Combining our data with observations from Europe, USA and PPTA will allow us to make a significant improvement on our time scale Contributions to BIPM check/correct long-term timing irregularities Improvement for GW-detection Time transfer Experiment in the space orbit CSIRO. Gravitational wave detection

New Clock Reference for Pulsar Timing L: TAI-TT(BIPM2010); R: TAI-TT(ppta) JUMP –f e-07 MJD(20cm_fptm) H-OH_cpsr2m 0.428 H-OH_cpsr2n 1.143 Ref:MULTI_cpsr2n MULTI_fptm -5.819 20cm_fb -40 MULTI_cpsr2m -0.255

What the PT could do? Time Keeper for long-term scale Correction for atomic clock Combining our data with observations from Europe, USA and PPTA will allow us to make a significant improvement on our time scale Contributions to BIPM check/correct long-term timing irregularities Improvement for GW-detection Time transfer Experiment in the space orbit CSIRO. Gravitational wave detection

PT wheel for time transfer

PT wheel for time transfer

What a PT could do? Time Keeper for long-term scale Correction for atomic clock Combining our data with observations from Europe, USA and PPTA will allow us to make a significant improvement in our time scale Contributions to BIPM check/correct long-term timing irregularities Time transfer Improvement for GW-detection Distant Time Comparasion CSIRO. Gravitational wave detection

展望 脉冲星是目前宇宙中最稳定的时间频率源 原子时的劣势如长期稳定度、连续性等刚好是PT的优势 深空探测的需求 空间时间基准的建立 超远距离时间比对（空间） 更多的应用等待你我去研究、去发掘！ 中国应该建立自己的PT！

Introduction to NSSC National Space Science Center Newly established on 7th, July 2011. based on CSSAR In charge of overall planning for the country’s space science to manage space science missions as a series Geo-space Double Star Exploration Program (DSP), CLUSTERS. Meridian Space Weather Monitoring Project Lunar Exploration Program (Chang’e) Mars Mission(Yinghuo-1) Manned Spacecraft Project Strategic Pioneer Project of Space Science

Strategic Pioneer Project of Space Science HXMT,Hard X-ray Modulation Telescope, ~2014 Kua’Fu mission, Space weather between sun-earth,~2015 Dark Matter Detection Satellite,~2015 SJ-10, space-microgravity and space-bioscience, etc., Lab. ~2015 Quantum Teleportation Satellite ,~2016 Some followed projects in next 5 years. Budget: ~4 billion

新技术研究室简介 瞄准空间科学探索技术需求前沿，前瞻性地开展和布局关键性新技术的研究开发。积极探索和发展空间科学与应用新需求、新技术和科学卫星计划，发掘相关新型关键技术的研究与应用，进一步促进相关空间科学任务的实施与应用，为推动空间科学的创新与空间应用的发展做出应有的贡献。 目前主要开展系外类地行星探测研究、空间天文导航、脉冲星计时与应用，短波成像仪器、新型探测器、空间高精度测量与成像等研究，承担中科院空间科学先导专项背景型号项目系外类地行星探测计划（STEP）总体，空间科学卫星夸父计划、太阳极轨射电成像望远镜计划（SPORT）背景型号等卫星有效载荷设计与研制任务。

系外类地行星探测计划(STEP) Search for Terrestrial Exo-Planets

宇宙“秘史”探测计划(DAD)

脉冲星应用研究感兴趣的同学和朋友加入我们！ 欢迎对空间科学、系外行星探测和 脉冲星应用研究感兴趣的同学和朋友加入我们！ 手机： 188 1105 0330 Email： ding@nssc.ac.cn

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Discussions Consistency Precision Validity Application

Statistics for Clock Stabilities Allan Deviation: (Allan, D 1987) , SigmaZ: (Matsakis, Taylor et al. 1997) Fittng the data by X(R)=c0+c1(R-R0)+c2(R-R0)2+c3(R-R0)3 with minimizing , τ=2-n×T, n=1,2,3,4,5