0. Table of contents

Last Updated 27 Apr 2023


1.  Timing Calibrations of X-ray missions

1.1 Summary of Timing Requirement and Calibrations

Note: 
(star) Past Missions, (blue star) Future Mission
(info) The "Offset" is defined as the average value of the difference time from the reference time, which is defined in the "Reference Time" column.
The "Deviation" represents the fluctuations in "Offset" time that have been observed many times.

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

ValueDescription
TAIEngineering 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
Otherdefinition is defined in "Note" column



Mission/InstrumentsScience Requirement Absolute TimeTiming System DesignTiming Calibration StatusIn-orbit Timing
Calibration Targets
Reported IssuesReference
RequirementGoalGPS ReceiverClock StabilityOffset from the Reference (info)Deviation, sigma(info)Reference Time (info)(question)Notes
RXTE/PCA (star)10μsec noneNo
 

Calibrated:
1 μsec

Uncalibrated:
~0 usec

(Absolute, not relative to radio)

Calibrated:
3.4 μsec

Uncalibrated:
100 usec (max)
~50 usec (std)
TAICalibration:
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(star)10 μsec noneSee aboveSee 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?)NoneHXTE Timing (10.1086/305377)
Chandra/ACIS0.25625 s
(one minor
frame start time)
0.001 s
(synchronize
minor frame starts)
No
(sync DSN)
3.2 μsec285 ± 6 μsec

Number is dominated by estimated engineering systematic uncertainty. Further analysis is required to figure out offset from Crab.
None at presentDavis et al. 2003
(davis.pdf)
Chandra/HRC
16 μsec4 ± 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-PN1 msnoneNo-

-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 μsec61 μsecRadio(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/BAT100 ms100 usecNo~ 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 presentG. 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(star)

No science requirement defined.No
(sync. ground)

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

Not confirmed.N/AN/A
A0535+262, Her X-1, etcN/A
Y.Terada et al 2008
(10.1093/pasj/60.sp1.S25)
Suzaku/HXD(star)

~ 70 μsec


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/FPMShould be 100 msnoneNo

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/LAXPCNone definedYes
(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/CZTINone definedYes
(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

Yes3 x 10^-8 s/s24.7 µs12.1 µs

Xray(NICER, NN us)The offset is with respect to NICERCrab (with NICER)


Youli Tuo
et al 2021

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

Insight-HXMT/ME10.1 µs8.6 µsXray(NICER, NN us)The offset is with respect to NICER
Insight-HXMT/LE864.7 µs15.8 µsXray(NICER, NN us)The offset is with respect to NICER
Hitomi/SXS, SXI, HXI, SGD(star)350 μsec
35 μsecYes

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/XTI100 ns (RMS)noneYesN/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 (blue star)1 msecnoneYessame 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 (blue star)10 msecnoneYes< 10 ms< 10 ms
the mission requirement values.(under discussion)



1.2 Point of Contacts

MissionPoC (last updated 27 Apr 2023)
RXTECraig Markwardt, Arnold Rots
ChandraVinay Kashyap, Arnold Rots
XMM-NewtonFelix Fuerst, Simon Rosen
SwiftAmy Lien, Giancarlo Cusumano
INTEGRALGuillaume Belanger, Volodymyr SAVCHENKO,Lucien Kuiper
NuSTARMatteo Bachetti, Katja Pottschmidt
Astrosat

Gulab Dewangan, Dipankar Bhattacharya

HXMTXiaobo LI
NICERCraig Markwardt, Teruaki Enoto
eROSITAMichael Freyberg
SuzakuYukikatsu Terada
HitomomiYukikatsu Terada
XRISMYukikatsu Terada, Megumi Shidatsu
Einstein ProbeJuan Zhang




2. In-orbit Timing Calibration Plan/Observations

2.1 Archive Data

2.1.1 List of Coordinated Observations useful for Timing
2.1.2 Reports

2.2 New Coordinated 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.




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

(after 14th IACHEC meeting in Japan)







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