Pulsar Radio Emission Altitude from Curvature Radiation

Abstract

We assume that relativistic sources moving along dipolar magnetic field lines emit curvature radiation. The beamed emission occurs in the direction of tangents to the field lines, and to receive it, the sight line must align with the tangent within the beaming angle 1= , where is the particle Lorentz factor. By solving the viewing geometry in an inclined and rotating dipolar magnetic field, we show that at any given pulse phase, the observer tends to receive radiation only from the specific heights allowed by the geometry. We find that outer conal components are emitted at higher altitudes compared to inner components, including the core. At any pulse phase, low-frequency emission comes from higher altitudes than high-frequency emission. We have modeled the emission heights of pulse components of PSR B0329+54 and estimated field line curvature radii and particle Lorentz factors in the emission regions.

Visibility of Pulsar Emission: Motion of the Visible Point

“…This corresponds to θ bV = θ bL (φ b ) at φ b = φ bV , and reproduces the result given by Gangadhara (2004):…”

“…In the RVM the line of sight is assumed to pass through the centre of the star, and the visible point is identified as its intersection with the sphere of radius r. The RVM should be regarded as an approximation to the standard model because the fixed line of sight through the centre of the star is not tangent to the field line (with the exception of the special case where the line of sight also intersects the magnetic pole). The tangent model, which was analysed by Gangadhara (2004), is exact in the sense that the line of sight varies so that it is always tangent to the field line.…”

“…The widely accepted rotating vector model (RVM) is an approximation in which the line of sight is fixed and the field line is not strictly tangent to it. We refer to an exact treatment (Gangadhara, 2004) as the tangent model. In the tangent model (but not in the RVM) the visible point changes as a function of pulsar rotational phase, ψ, defining a trajectory on a sphere of radius r. We solve for the trajectory and for the angular velocity of the visible point around it.…”

Neutron Star Physics in the Square Kilometre Array Era: An Indian Perspective

“…Although this hypothesis has gained wide acceptance, it must be tested by measurements using the widest possible bandwidths, the highest possible time resolution and the best possible sensitivity of the proposed SKA. An extreme antithetical model is one in which the emission is infinitely beamed radiating tangentially to the local magnetic field lines (Gangadhara 2004).…”

Absolute emission altitude of pulsars: PSRs B1839+09, B1916+14, and B2111+46

“…Results. We have been able to locate the phase location of the meridional plane and to estimate the absolute emission altitude of both the core and the conal components relative to the neutron star center, using the exact expression for the A/R phase shift given by Gangadhara (2005). …”