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CRABTIME: Help

CRABTIME - Crab Pulsar Timing


Overview

The CRABTIME database contains the Crab Pulsar Monthly Ephemeris covering the period from Feb 15 1982 (MJD=45015) to (close to) the present that was created Dr. Andrew Lyne and collaborators at Jodrell Bank Observatory. This database is periodically updated to include recent data as these become available. To assist astronomers, the HEASARC has created two new parameters which were not present in the original Jodrell Bank tables, the pulsar period and its first derivative, using the standard relations between period (P) and frequency `Nu` (P=1./Nu) and their first derivatives (P_dot = -Nu_dot/Nu^2). The assumed pulsar position used in the reductions is
RA (1950.0) 05 31 31.406  DEC (1950.0) +21 58 54.391
RA (2000.0) 05 34 31.973  DEC (2000.0) +22 00 52.061

Bulletin

The CRABTIME database table was last updated on 23 February 2009.

References

Lyne, A.G., Jordan, C.A., Roberts, M.E., "Jodrell Bank Crab Pulsar Timing Results, Monthly Ephemeris", http://www.jb.man.ac.uk/~pulsar/crab.html (University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire, SK11 9DL, UK.

Provenance

This HEASARC version of the "Jodrell Bank Crab Pulsar Timing Results, Monthly Ephemeris" is updated within one week of any changes to the tables available on the Web at http://www.jb.man.ac.uk/~pulsar/crab.html.

Reduction Description

Examples of reduction of site arrival times to the Solar System barycentre and infinite frequency using the JPL Ephemeris DE200:

Pulses were observed at the following places, frequencies, and times(UTC):

   Wardle      609.981 MHz.       02 JULY 1983 15:26:27.521969
   Wardle      609.981 MHz.       27 JULY 1983 16:02:32.558116
   Jodrell     610.000 MHz.       15 JAN  1989 16:08:49.060034
   Jodrell     608.000 MHz.       12 FEB  1989 14:08:36.094064

The telescope site co-ordinates are:

           r x cos(lat)        r x sin(lat)        long(hours west)
Wardle     3836.629 kms        5078.151 kms        0.173066
Jodrell    3825.684            5086.391            0.153740

The corrections applied are as follows:

                                     02 JULY 1983       27 JULY 1983
                                     15:26:27.521969    16:02:32.558116
 UTC      to       TAI                    +22.000000         +22.000000
 TAI      to       TDT                    +32.184000         +32.184000
 TDT      to       TDB                     +0.000054          -0.000639
 Wardle   to   Earth centre                +0.011222          +0.004404
 Earth centre to  Barycentre            -8:02.243380       -6:22.406452
 observed freq to infinite freq            -0.633679          -0.633725
 Gravitational propagation delay           -0.000038          -0.000021

Corrected BC arrival time            15:19:18.840148    15:57:03.705684
BC arrival time from ephemeris       15:19:18.840180    15:57:03.705690

                                     15 JAN 1989        12 FEB 1989
                                     16:08:49.060034    14:08:36.094064
 UTC      to       TAI                    +24.000000         +24.000000
 TAI      to       TDT                    +32.184000         +32.184000
 TDT      to       TDB                     +0.000348          +0.001062
 Jodrell   to  Earth centre                +0.006671          +0.006146
 Earth centre to  Barycentre            +6:58.424915       +4:07.211028
 observed freq to infinite freq            -0.633435          -0.637457
 Gravitational propagation delay           -0.000001          -0.000003

Corrected BC arrival time            16:16:43.042532    14:13:38.858840
BC arrival time from ephemeris       16:16:43.042540    14:13:38.858881

Parameters

RA
The Right Ascension of the Crab Pulsar. The assumed pulsar position used in the reductions is as follows:

  RA (1950.0) 05 31 31.406  DEC (1950.0) +21 58 54.391
  RA (J2000)  05 34 31.973  DEC (2000.0) +22 00 52.061
  

Dec
The Declination of the Crab Pulsar. The assumed pulsar position used in the reductions is as follows:

  RA (1950.0) 05 31 31.406  DEC (1950.0) +21 58 54.391
  RA (J2000)  05 34 31.973  DEC (2000.0) +22 00 52.061
  

LII
The Galactic Longitude of the Crab Pulsar.

BII
The Galactic Latitude of the Crab Pulsar.

Day
The day of the ephemeris entry.

Month
The month of the ephemeris entry.

Year
The year of the ephemeris entry.

MJD
The Modified Julian Date of the ephemeris entry. The Modified Julian Date (MJD) is the Julian Date (JD) - 2400000.5 days.

MIT_Time
`MIT Time` is the arrival time using the M.I.T.(PEP311) ephemeris (Ash, M.E., Shapiro, I.I., & Smith, W.B. 1967, AJ, 72, 338). The arrival times given are those of the centre of the first main pulse after midnight at infinite frequency at the barycentre of the solar system, in seconds. The timescale is now quoted in terms of T.D.B. To convert to T.A.I., 32.184 seconds must be subtracted. The MIT ephemeris only covers the dates up to Feb 1990. This parameter was given to a precision of 10^-6 seconds in the original table.

JPL_Time
`JPL Time` is the arrival time obtained using the JPL (DE200) ephemeris (Standish, M. 1982, A&A, 114, 297). The arrival times given are those of the centre of the first main pulse after midnight at infinite frequency at the barycentre of the solar system, in seconds. The timescale is quoted in terms of T.D.B. To convert to T.A.I., 32.184 seconds must be subtracted. This parameter was given to a precision of 10^-6 seconds in the original table.

T_Acc
The accuracy in microseconds with which the ephemeris defined from these numbers is believed to describe the observed arrival times during the whole calendar month, using the DE200 ephemeris. If the PEP311 ephemeris is used, then the difference in `Nu` is approximately 1 part in 1E-10, corresponding to a maximum arrival time difference over a month of less than 250 microseconds.

Nu
The observed barycentric frequency `Nu` in Hertz (Hz), and its first derivative `Nu Dot`, are given at the quoted arrival time, using the DE200 ephemeris. This parameter was given to a precision of 10^-10 Hz in the original table.

Nu_Error
The uncertainty in the observed barycentric frequency `Nu`, in Hertz (Hz).

Nu_Dot
The first derivative `Nu Dot` of the observed barycentric frequency `Nu`, in units of s^-2, and given at the quoted arrival time, using the DE200 ephemeris. This parameter was given to a precision of 10^-17 s^-2 in the original table.

Nu_Dot_Error
The uncertainty in the first derivative `Nu Dot` of the observed barycentric frequency `Nu`, in units of s^-2.

Period
The observed period, in seconds, calculated by the HEASARC from the reciprocal of the observed barycentric frequency `Nu`.

Period_Dot
The first time derivative of the period, in units of s/s, calculated by the HEASARC from the standard relation P_dot = - Nu_dot/Nu^2.

DM
The dispersion measure, as observed, is usually given, the error being typically 0.005 pc cm^-3. If the value of the dm_flag parameter is 'Y', this indicates that the quoted dispersion measure is an assumed value, extrapolated from adjacent data.

DM_Flag
This parameter is set to 'Y' to indicate that the particular dispersion measure is an assumed value, extrapolated from adjacent data.

Delay
The assumed delay in microseconds due to interstellar scattering for 408 MHz. Where measured at other frequencies, the amount of scattering is assumed to scale as radiofrequency to the inverse 4th power.

Note_Number
A code number indicating that there is a note for the particular entry. The meaning of the codes is as follows:

    7  --  The end of the fit for AUG 1986 and the beginning of the fit for SEPT
  1986 is taken as MJD 46664.0, that is midnight on 22 AUG 1986. This is the
  date of a significant glitch. (See Lyne, A.G., & Pritchard, R.S. 1987, NMRAS,
  229, 223).

    8  --  The end of the fit for AUG 1989 and the beginning of the fit for SEPT
  1989 is taken as MJD 47767.4, that is 09:30 on 29 AUG 1989. This is the date
  of a large glitch.

    9  --  The fits with epochs 2 SEP, 11 SEP, and 23 SEP cover the dates 29 AUG
  09:30 to 7 SEP 00:00, 7 SEP 00:00 to 15 SEP 00:00, and 15 SEP 00:00 to 1 OCT
  00:00, respectively.

   11  --  The end of the fit for NOV 1992 and the beginning of the fit for DEC
  1992 is taken as MJD 48945.8, that is 19:30 on 19 NOV 1992. This is the date
  of a significant glitch.

   12  --  The end of the fit for JUN 1996 and the beginning of the fit for JULY
  1996 is taken as MJD 50259.9, that is 25 JUN 1996. This is the date
  of a significant glitch.

   13  --  The beginning of the fit for OCT 1999 is taken as MJD 51454.1, that
  is 00:00 on 3 OCT 1999. There was a significant glitch at MJD 51452.3, that
  is 1 OCT 1999.

   14  --  The end of the fit for JULY 2000 and the beginning of the fit for AUG
  2000 is taken as MJD 51739.4, that is on 14 JULY 2000. This is the date
  of a significant glitch.

   15  --  The end of the fit for SEPT 2000 and the beginning of the fit for OCT
  2000 is taken as MJD 51804.9, that is 17 SEPT 2000. This is the date
  of a significant glitch.

   16  --  The end of the fit for JUNE 2001 is taken as MJD 52083.8, that is on
  24 JUN 2001. This is the date of a significant glitch.

   17  --  The end of the fit for AUG 2001 is taken as MJD 52146.0, that is on
  24 AUG 2001. This is the date of a significant glitch.
  

Contact Person

Questions regarding the CRABTIME database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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