Page History

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"Reference Time" column is defined as follows; (not ready on 20 May 2022)

Value	Description
TAI	Engineering value. The reference time is the International Atomic Time (TAI)
Radio (II)	Radio ephemeris of Crab main pulse by II Observatory. ex) II: Jodrell Bank radio observatory
*Xray(II, NN us)*	X-ray ephemeris of Crab main pulse by the Instrument (II), assuming the timing reference from radio main pulse is NN usec. ex) II: NICER, NN: 350 usec
*Gamma(II, NN us)*	Gamma-ray ephemeris of Crab main pulse by Fermi LAT, assuming the timing reference from radio main pulse is NN usec ex) II: Fermi LAT, NN: 350 usec
Other	definition is defined in "Note" column

Mission/Instruments

Science Requirement Absolute Time

Timing System Design

Timing Calibration Status

In-orbit Timing
Calibration Targets

Reported Issues

Reference

Requirement

Goal

GPS Receiver

Clock Stability

Offset from the Reference

Deviation, sigma

Reference Time

Notes

RXTE/PCA

10μsec

none

No

Calibrated:
1 μsec

Uncalibrated:
~0 usec

(Absolute, not relative to radio)

Calibrated:
3.4 μsec

Uncalibrated:
100 usec (max)
~50 usec (std)

TAI

Calibration:
Spline-based calibration against ground timing standards, including ground time assignment error.

Uncalibrated:
Mission operations maintained on-board clock to within 100 usec of UTC using clock frequency steering

PSR B1821-24 60 μsec

Before 1997-04-29, increased timing jitter 8 μsec

rxte_time.html

Timing Budget
Jahoda et al. 2006 (10.1086/500659)

PSR B1821
Rots et al. 1998
(10.1086/305836)

Crab
Rots et al. 2004
(10.1086/420842)

RXTE/HEXTE

10 μsec

none

See above

Event by event has 7.6 μsec resolution.

"the HEXTE absolute time reference is accurate within a fraction of a millisecond.(10.1086/305377)"

delay 0-1 μsec (corrected?)

None

HXTE Timing (10.1086/305377)

Chandra/ACIS

0.25625 s
(one minor
frame start time)

0.001 s
(synchronize
minor frame starts)

No
(sync DSN)

3.2 μsec

285 ± 6 μsec

Number is dominated by estimated engineering systematic uncertainty. Further analysis is required to figure out offset from Crab.

	None at present	Davis et al. 2003 (davis.pdf)
Chandra/HRC

16 μsec

4 ± 4 μsec

Crab
PSR B1821-24

Note: Precision relative to RXTE.

Due to a wiring problem, photon time tag gets attached
to next event; correctable
under special mode for
HRC-S which telemeters
all events and then
reassigns times on the
ground. In order to avoid telemetry saturation, a higher value of the lower-level discriminator is set, which causes low PHA events to be discarded on board. This results in significant loss in QE for epochs when gain is low.

Davis et al. 2003
(davis.pdf)

Rots 2006
(CXOClock.pdf)

XMM-Newtion/EPIC-PN

1 ms

none

No

-

-354±11 μsec

108 μsec ( 1 sigma)

Note: Timing = -306 +/- 16 μsec, Burst = -387+/-13 μsec.
Timing mode is affected by pile up.

Note: XMM-Newton EPIC-MOS was deleted from the table.

Crab pulsar (bi-annual)

None currently

Kirsch et al, SPIE, 5165, 85
(10.1117/12.503559)

Martin-Carrillo et al, A&A, 545, A126 (2012)
(10.1051/0004-6361/201116576)

~~CAL-TN-0220-1-4.pdf (Limited access)~~

CAL-TN-0220-1-5.pdf

INTEGRAL/SPI

L.Kuiper 2003
(10.1051/0004-6361:20031353)

L.Kuiper 2019
(13th IACHEC PDF)

INTEGRAL/IBIS

-248±2 μsec

61 μsec

Radio(Jodrell Bank)

Offset is w.r.t. radio main-pulse using ISGRI 20-100 keV data
collected during INTEGRAL Revolutions 47 - 1877
(last date Oct. 23, 2017); Jodrell Bank radio eph. folding

same above

Swift/BAT

100 ms

100 usec

No

~ 6.572 x 10^-8 s/s

Uncalibrated: tens of seconds

Calibrated:
~50 μs

Uncalibrated:
N/A

Calibrated:
~ 50 μs

Xray(RXTE, 344 us)

BAT instrument has 100 usec time-stamping quantization, which is dominant term in uncertainty.

Offset is found by comparing RXTE PCA and Swift BAT observations of Crab (Cusumano et al 2012)

Clock measurements made by mission operations & ground station, and applied as calibration when barycentering.

Crab pulsar (annual)

None at present

G. Cusumano et al 2012
(10.1051/0004-6361/201219968)

BAT team wiki page;
private communication
with Michael Tripicco
see BAT Wiki: Pre-launch Timing,
BAT Wiki (410.4-SPEC-0005F.pdf)
(Limited Access)

Swift/XRT

~ 10 ms

No

Calibrated:
~ 270 μs

Xray(RXTE, 344 us)

Clock measurements made by mission operations & ground station, and applied as calibration when barycentering.

Crab pulsar

None at present

G. Cusumano et al 2012
(10.1051/0004-6361/201219968)

D. Burrows et al. 2005
(10.1007/s11214-005-5097-2)

Suzaku/XIS

No science requirement defined.

No
(sync. ground)

1.9 x 10^-9 s/s
(measured)

Not confirmed.

N/A

	A0535+262, Her X-1, etc	N/A	Y.Terada et al 2008 (10.1093/pasj/60.sp1.S25)
Suzaku/HXD	~ 70 μsec		Y.Terada et al 2008 (10.1093/pasj/60.sp1.S25)

360±150 μsec (90%)

(270±130 μsec
in condition)

Xray(RXTE,Integral, 330 us)

“offset” is defined from the difference from
the average arrival time of Crab among X-ray missions
and the HXD in the simultaneous observation of Crab.

Crab for coordinated
PSR1509-58

Timing shift by a failure
in time stamp at the
ground station during
2012-2014
(Shu Koyama, Fixed)

NuSTAR/FPM

Should be 100 ms

none

No

Freely drifting by ~3 ms/day.
Reduced to 20 us/day using
the clock correction file

65 μs (1-sigma)

Crab
B1821-24A
B1937+21

~5ms offset using
millisecond pulsars
(Lucien Kuiper)

Corrected through
clock correction file
v108+

Bachetti+ in prep
(can distribute early copy)

Fermi/LAT

-111 ±4µs

57 µs

Radio(Jodrell Bank)

9 years of LAT data; see also Sci. 334, 69 (2011)
for 9 months after launch
value of -138 us +/- 12 us +/- 21 us;
Jodrell Bank radio eph. folding


Fermi/GBM (BGO)

-222 ±4µs

56 µs

Radio(Jodrell Bank)

100-300 keV band; data from Nov-2012
up to incl. Jan-2018;
Jodrell Bank radio eph. folding


Fermi/GBM (NaI)


AstroSat/LAXPC	None defined	Yes (offline referral)	4 μsec rms after GPS synchronization	316 ±70µs	118 µs (rms)	Gamma(Fermi, NN us)	The offset is with respect to Fermi-LAT ephemeris	Crab Pulsar (with Radio)	None at present	D. Bhattacharya 2017 (10.1007/s12036-017-9461-x) Basu et al (in prep)
AstroSat/CZTI	None defined	Yes (offline referral)	3 μsec rms after GPS synchronization	-650 ±70µs	83 µs (rms)	Gamma(Fermi, NN us)	The offset is with respect to Fermi-LAT ephemeris	Crab Pulsar (with Radio) GRBs	None at present	D. Bhattacharya 2017 (10.1007/s12036-017-9461-x) Basu et al 2018 (10.1051/0004-6361/201832913) Basu et al (in prep)
Insight-HXMT/HE

Yes

3 x 10^-8 s/s

24.7 µs

12.1 µs

Xray(NICER, NN us)

The offset is with respect to NICER

Crab (with NICER)

Youli Tuo et al 2021

(https://arxiv.org/abs/2109.04709)

Insight-HXMT/ME

10.1 µs

8.6 µs

Xray(NICER, NN us)

The offset is with respect to NICER


Insight-HXMT/LE	864.7 µs	15.8 µs	Xray(NICER, NN us)	The offset is with respect to NICER


Hitomi/SXS, SXI, HXI, SGD	350 μsec	35 μsec	Yes	0.01μsec(GPSR) <3.0 μsec(SpW) 0.3 ns (orbit)	~ 120-230 μsec	<3.0 usec (3 sigma)	Radio(NICT)

Crab (with radio)
note: using out-of-time
event for SXI

absolute timing
accuracy is much
larger than expected
on ground (3 μsec)

Y.Terada et al 2018
(10.1117/1.JATIS.4.1.011206)

NICER/XTI

100 ns (RMS)

none

Yes

N/A

Uncalibrated:
1 second

Calibrated:
Approx <3 us based on Crab

Calibrated:
Measured <400 ns based on ground cal

(Absolute, not relative to radio)

100 ns (RMS) [requirement]

TAI

The NICER XTI timing system was calibrated on ground using an end-to-end system, with GPS simulator and precision X-ray pulse generator. Detector + system time delays of ~400 ns are included in the calibration.

Combined error / noise terms designed to be < 100 ns (including GPS, X-ray detection, barycentering)

Absolute timing offset values depend on the definition of absolute timing.
See supplementary material of this paper(https://science.sciencemag.org/content/372/6538/187),
Figure S12 and S13 [p.33-34] for
the NICER Crab X-ray main peak monitoring.
At this stage, it is not clear whether
the fluctuation of the peak phase is
due to the instrumental effects
or due to intrinsic of the pulsar.

Crab Pulsar
PSR B1821-24A
PSR B1937+21

Precise 1-second offset
in on-board timestamps
due to flight software bug;
corrected using TIMEZERO
keyword in pipeline-processed
FITS data files.
(see HEASARC page for detail)

Markwardt et al. (in prep.)

eROSITA


XRISM/Resolve	1 msec	none	Yes	same as Hitomi	<1 ms	<1 ms

the values (1 msec) are the requirement
including both offset and deviation.

(under discussion)

		See In-flight Calibration Plan in IACHEC 2021 virtual meeting; xrism_ifcp_iachec_20210416.pdf
XRISM/Xtend	10 msec	none	Yes	< 10 ms	< 10 ms

the mission requirement values.

(under discussion)

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1.2 Point of Contacts

Mission	PoC (last updated 27 Apr 2023)
RXTE	Craig Markwardt, Arnold Rots
Chandra	Vinay Kashyap, Arnold Rots
XMM-Newton	Felix Fuerst, Simon Rosen
Swift	Amy Lien, Giancarlo Cusumano
INTEGRAL	Guillaume Belanger, Volodymyr SAVCHENKO,Lucien Kuiper
NuSTAR	Matteo Bachetti, Katja Pottschmidt
Astrosat	Gulab Dewangan, Dipankar Bhattacharya
HXMT	Xiaobo LI
NICER	Craig Markwardt, Teruaki Enoto
eROSITA	Michael Freyberg
Suzaku	Yukikatsu Terada
Hitomomi	Yukikatsu Terada
XRISM	Yukikatsu Terada, Megumi Shidatsu
Einstein Probe	Juan Zhang

...

2. In-orbit Timing Calibration Plan/Observations

...

Semi-simultaneous observation of Crab with XRISM and NICER in 2023-2024 (last updated 27 Apr 2023)
- When: Dec 2023 – June 2024 (assuming XRISM launch in Aug 2023)
- Missions & PoC
  - XRISM (Yukikatsu Terada)
  - NICER (Craig Markwardt)
  - Radio in Japan (Teru Enoto; to be confirmed)
  - HXMT(Xiaobo Li)
  - EP (Juan Zhang) … not decided yet
new plan here.

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3. Studies on Timing

3.1 effects on timing products (power spec, light curve etc) by the detector’s behavior (dead time, grade selection of calorimeter etc)

...

4. Timing Tools, (with Statistic Group)

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5. Working Group Meeting Notes

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- 28 April 2020
  20200428_IACHEC_Time_WG_notes.pdf
- 15 Sep 2020
  20200915_IACHEC_Time_WG_notes.pdf
- 20 April 2021
  20210420_IACHEC_Time_WG_notes.pdf
- 12 May 2021
  20210512_IACHEC_Time_WG_notes.pdf
- 15 Oct 2021
  20211015_IACHEC_Time_WG_notes.pdf
- 13 May 2022
  20220513_IACHEC_Time_WG_notes.pdf

...

- 15 May 2024
  20240515_16thIACHEC_TimingWG_discussion_Items_Note.pdf
  (for reference: 16thIACHEC_TimingWG_summary_mod.pdf)
- 1 July 2024
  20240701_IACHEC_Time_WG_notes.pdf

Child pages

Versions Compared

Old Version 61

New Version Current

Key

1.2 Point of Contacts

2. In-orbit Timing Calibration Plan/Observations

3. Studies on Timing

3.1 effects on timing products (power spec, light curve etc) by the detector’s behavior (dead time, grade selection of calorimeter etc)

...

4. Timing Tools, (with Statistic Group)

...

5. Working Group Meeting Notes