Latest Observation Results

PDMP Period Search Result

The image just below is the output of a PDMP period search.   The top 5 lines contain information about the observation.  The four plots are

1. Top-left: a bulls-eye plot of the search matrix results of steps through a DM range against fold period.  A nice compact spot in the middle is a sign of a successful period search.

2. Middle-left: Phase-vs-Time - shows the pulse strength over the time of the observation.  For a pulsar with strong scintillation the pulse trace might come and go over the observation - but Vela shows little variation between the ~100 second sub-integrations.  A perfectly vertical blue line indicates that the ephemeris used is accurate.   A glitch - where the period decreases abruptly - would cause the blue line to tilt to the left as the pulses would arrive earlier than predicted by the current ephemeris.

3. Middle-right: Phase-vs-Frequency - shows the strength over the observation bandwidth.  The narrow bandwidth (2.4 MHz) means that any variation across the observation bandwidth would be due to front-end filter responses.   A perfectly vertical blue line indicates the signal has been de-dispersed at the correct DM.

4. Bottom-left: Pulse Profile.  This plot is the pulse signal integrated over the whole observation time and bandwidth.  A signal-to-noise ratio (S/N) is derived from the profile - although for a S/N less than about 15 this is likely inaccurate.

NOTE: the above image is not the last result - but is a representative example of a good result from a past observation.

GNUPLOT Data Plots

Three plots are presented below...

1. Measured Barycentric Period vs MJD

2. Measured Period Offset from Ephemeris vs MJD

3. Signal-to-Noise Ratio vs MJD

Measured Barycentric Period Notes

As the pulsar spins it loses energy and so gradually spins slower.   Consequently the observed spin period grows larger over time.  The term 'barycentric' refers to the observed period (topocentric) corrected for the motion of the Earth-based observer - in the first order the motion of the Earth around the Sun and its daily rotation.  The term 'MJD' refers to the modified Julian Day.

Measured Period Offset Notes

In order to predict the normal pulsar spin down over time an ephemeris is needed.   This ephemeris contains - starting from a given MJD (epoch) - a spin frequency term and usually a first (rate of change in spin frequency) and second (rate of change in the rate of change in spin frequency) derivatives - designated F0, F1 and F2 respectively.  Measured period offsets can be non-zero due to an incorrect ephemeris (or more usually an outdated ephemeris as Vela glitches every couple of years - accordingly the ephemeris used at HawkRAO is derived locally).  Other causes of a deviation are low S/N, radio frequency interference (RFI) contamination, inaccurate sampling clock or - more hopefully - a glitch.  If a glitch occurs it should show up in this graph as a negative jump in offset - provided its magnitude is greater than the noise on the period measurement by a significant amount.  Note that the largest glitch so far observed had a magnitude of -3.16 ppm (MJD 51559) as marked on the plot.  The maximum negative range is set at -5 ppm - but it is unlikely that a glitch much more than -3 ppm will occur - although not impossible.

Ideally the period offset shown in the following plot should hug zero over time - indicating an accurate ephemeris.   Analysis of any significant deviation of the blue plotted measurement points from that ideal can provide a guide to an update of the ephemeris according to the following...

•  Tracks linearly parallel - but offset = error in F0

• Tracks linearly away = error in F1

• Tracks with a curvature = error in F2

Corrections will be done if deviations become significant.

Current Ephemeris Derived from HawkRAO Observations

Epoch: 59719.279304
F0:  11.1838223320897
F1:  -1.57544558632375 E-11
F2:  5.74361029675338 E-21

NOTES:

1. Precision far exceeds accuracy - the values are outputs from a polynomial least-squares fit of HawkRAO data at S/N levels averaging 17.

2. The above values for F0, F1 and F2 include sampling clock errors as well as errors in radial velocity calculations - accuracy limited to about +/-2 ppm.

Signal-to-Noise Notes

This plot is indicative only.   The source of the variations in S/N is not confined to the intrinsic flux density from the pulsar - but are heavily influenced by RFI.  As such, day-to-day variations should be ignored and only long-term trends warrant attention.   Sudden drops in S/N for Vela are more likely system failures - as a recent experience with a defective coaxial cable line demonstrated.

Invalid Results

Very occasionally the analysis returns invalid results. A 'rogues gallery' of some examples can be seen here.