Can a pulsar have an axial tilt close enough to $90^\circ$ to hit us with both beams for two pulses per rotation?

  • 2
    $\begingroup$ Are your interested in theory of orientations, or whether there's ever been an observed pulsar with significant axial tilt? $\endgroup$ – Carl Witthoft May 6 '20 at 14:55
  • $\begingroup$ @CarlWitthoft Theory is the focus of the question, but if it fits as a minor addendum to an answer, information about actual observations is appreciated. Presumably if we've seen such pulsars, then we know it's possible, and if we currently think it's impossible, we haven't seen any. $\endgroup$ – smithkm May 7 '20 at 19:51

Yes. One of the features that helps this scenario is the gravitational bending of light close to the neutron star, which allows for a larger fraction of the surface to be visible at a given time.

Many pulsars have double-peaked light curves, for example here's the light curve of the Crab Pulsar. In the pencil beam model these peaks correspond to the beams from the two poles.

According to Annala & Poutanen (2010) "Constraining compactness and magnetic field geometry of X-ray pulsars from the statistics of their pulse profiles", the ratio of single-peaked to double-peaked pulsar light curves puts a most likely value for the maximum inclination of the magnetic axis relative to the rotational axis of 40°±4°.

  • $\begingroup$ Thanks, the term "double-peaked" was the key thing I was missing when I tried to look this up myself. $\endgroup$ – smithkm May 11 '20 at 0:24

It depends on where the beams are facing. If the magnetic poles are facing you and the spinning axis is facing the right position, then both can. So it depends on two things:

  1. Direction of magnetic poles
  2. Direction of spinning axis

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