The Pulsar Shadow as the Origin of Double Notches in Radio Pulse Profiles

We present the model of eclipsing a rotating, spatially extended source ofdirectional emission by a central absorber, and apply it to the pulsarmagnetosphere. The model assumes the radially extended inward radio emissionalong the local direction of the magnetic field, and the pulsar as theabsorber. The geometry of the magnetic field lines of the rotating dipole isfavourable for the double eclipse events, which we identify with the doublenotches observed in pulse profiles of nearby pulsars. For pulsars with largedipole inclinations 70 <~ alpha <~ 110 deg the double notches are predicted tooccur within a narrow phase range of 20 to 30 deg before the main radio peak.Application of the model to PSR B0950+08 establishes it as a nearly orthogonalrotator (alpha =~ 75 deg, beta =~ -10 deg) with many pulse components naturallyinterpreted in terms of the inward radio emission from a large range ofaltitudes. The inward components include the intermittently strong, leadingcomponent of the main pulse, which would traditionally have been interpeted asa conal emission in the outward direction. The model also identifies themagnetic field lines along which the radially extended inward radio emissionoccurs in B0950+08. These have a narrow range of the footprint parameter sclose to 1.1 (closed field line region, near the last open field lines). Wedescribe directional characteristics of inward emission from the radiallyextended region and compare them with characteristics of extended outwardemission. Our work shows that pulse profiles of at least some pulsars may be asuperposition of both inward and outward emission.