interpulses

Interpulses are secondary components observed in the rotation-powered radiation of some pulsars. In a pulsar's emission profile, there is a primary peak, the main pulse, and one or more additional peaks known as interpulses. The interpulse typically appears at a distinct rotational phase away from the main pulse and can be separated by about half a rotation, though the exact separation depends on geometry and emission altitudes.

Interpulse formation is commonly interpreted through pulsar geometry: either the observer's line of sight intersects emission from both magnetic poles during a single rotation (an orthogonal rotator scenario), or a single magnetic pole emits radiation in two separated beam regions such as double cones or patchy sub-beams, producing two pulses per rotation. In the first case, the phase separation tends toward 0.5; in the second, it may deviate.

Interpulse properties vary with frequency and pulsar type. They often show distinct polarization characteristics and may differ in spectral index from the main pulse, suggesting different emission heights or mechanisms. Long-term monitoring reveals that interpulses can be remarkably stable, but in some objects they exhibit mode changes or timing irregularities, complicating phase alignment and timing solutions.

Interpulses provide important constraints on pulsar magnetosphere models, including polar-cap, outer-gap, and slot-gap frameworks. By analyzing the separation, polarization, and energy dependence of the two peaks, researchers infer the geometry of the magnetic axis, the line of sight, and the altitude of the emission regions. The study of interpulses thus contributes to understanding radio and high-energy pulsar emission processes.