SLOP3255 · Week 04 · Periodic signals
The clocks of pulsars#
A pulse train sounds simple. The journey from rotating neutron star to folded profile is not.
One object, three clocks#
Rotation
A neutron star turns, sweeping a beam across space.
Arrival
A telescope timestamps energy received at Earth.
Playback
A designer chooses audio speed, grouping and emphasis.
Only the first two clocks belong to the astronomical measurement. The third belongs to us.
What arrives at the telescope?#
Individual pulses vary. Noise can be larger than a single pulse. The stable quantity is often recovered statistically across many rotations.
Interstellar space delays radio pulses#
| Frequency channel | Relative arrival | Before folding |
|---|---|---|
| high radio frequency | earlier | align to reference time |
| middle channel | later | remove predicted delay |
| low radio frequency | latest | remove larger delay |
This frequency-dependent delay is dispersion. Dedispersion is a scientific operation, not audio polishing.
Folding reveals the profile#
Folding reveals repetition by discarding the identity of individual rotations.
The folded profile is not a pulse recording#
It is an average shape by phase. A sonification must say whether it plays arrivals, rotations or the folded profile.
What folding removes#
Hidden by averaging
- pulse-to-pulse variation
- rare bright pulses
- short interference
Made visible
- stable phase structure
- weak repeated components
- profile comparison
The operation is valuable because it changes the question.
Timing residuals are the next signal#
Observed arrival time − predicted arrival time = residual.
Sonifying residuals shifts attention from pulse rhythm to model error.
Listening Lab 04 · Output: folded profile
Fold a pulsar#
Task
Find the period of a noisy synthetic pulse train, fold it and compare arrival-time audio with profile audio.
Explain
- what was aligned
- what averaging removed
- which audio answers which question
Reference: CSIRO Parkes Pulsar Timing Array · research.csiro.au/ppta/