Pulsar-based Time Scale
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
工程技术领域
国家重大系统
天文学、
信息传递、电力输配、
交通运输、电力、
物理学
深空探测、遥感测绘、
金融证券、
地球动力学、
导航定位、武器实验、
邮电通信
大地测量学
地震监测、计量测试
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！
Market Conditions
(Constraints/Contracts)
User Interface
EMS applications
for self-healing grid
State
Measurement
Input Data:
•10-60 Phasors/sec
•Control Device Status
•Control Range
Data Synchronization &
Control Coordination
C O
Wide Area Control
•On/Off
•Linear Control
•Operate Point change
Peace River
Kemano
Phasor
Measurement
Units
L O
Grand Coulee
Transmission Paths
McNary
John Day
Colstrip
Midpoint
Malin
Table Mtn.
IPP
PG&E
Navajo
Moss Landing
Diablo Canyon
Jim Bridger
SCE
LADWP
SDG&E
Hoover
Mohave
San Juan
Cholla Four Corners
Palo Verde
500kV Lines
345kV Lines
230kV Lines
DC Lines
N
T
R
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”与“间”：时刻 & 间隔
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。”
The Stabilities of
Frequency Scales
different
-9
Log (y())
-10
-11
-12
-13
-14
-15
-16
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
Log (), seconds
4.0
5.0
1 day
6.0
7.0
1 month
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 N 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.
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) :
N
(TAI  EPT)   ˆ k (TAI  PTk )
k  ( 2 k   2 z,k ( T ))2
k 1
 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?
TT(TAI)-TT(BIPM2010)
New Technique
 Define clock function to be simple Fourier expansion:
f (t)   Ak cos(k 0t) Bk sin(k 0t)
 (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)
T 1
1
T 1
P est  (M C M) M C R
Final result (PPTA data)
PT(PPTA)-TT(TAI) and TT(BIPM2010)-TT(TAI)
1ms
PT(ppta)-BIPM(2010) – time transfer?
PKS->TID>UTC(NIST)->TT
PKS->GPS->TT(TAI)
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 sunearth,~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)
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
谢谢！请指正！
Discussions




Consistency
Precision
Validity
Application
Statistics for Clock Stabilities
 Allan Deviation: (Allan, D 1987)
1
  ( yn  yn1 ) 2
2
2
y
, yn  ( xn  xn1 ) 
 SigmaZ: (Matsakis, Taylor et al. 1997)
Fittng the data by X(R)=c0+c1(R-R0)+c2(RR0)2+c3(R-R0)3 with minimizing [(R  X (R )) /  ]
2
i
 z ( ) 
2
2 5
2 1/ 2
,
3
c
i
τ=2-n×T, n=1,2,3,4,5
i