Multifrequency evolution of the Integrated pulse profile of radio pulsars by implementing the inverse Compton mechanism

TL;DR

The paper develops a self-consistent framework that combines curvature radiation from primary particles with inverse Compton scattering of low-frequency seed photons by secondary magnetospheric plasma to explain the multi-frequency evolution of pulsar pulse profiles. By embedding ICS within a dipolar-beam geometry and applying a Gaussian modulation template, the authors reproduce high-frequency conal components and beam–frequency diagrams for PSR B2111+46 and PSR B1933+16, showing how the scattering altitude and component spacing are tuned by a dissipation factor and plasma dynamics. The approach highlights the necessity of coupling intrinsic emission with propagation-modulated ICS to account for observed morphology changes across frequencies, while noting that propagation effects and aberration-retardation remain areas for future refinement. Overall, ICS provides a plausible mechanism for emergent high-frequency components, complementing coherent curvature emission and the magnetospheric propagation environment in shaping pulsar radio profiles.

Abstract

The Main Aim of this paper is to explain the emergence of new components of pulsars at higher radio bands by implementing the Inverse Compton Scattering Mechanism. From pulsar radio observation, it is seen that a couple of pulsars reveal new emission components at higher radio frequencies, although they show single-component emission at lower frequencies. We develop a brief outline, fostering inverse Compton scattering (ICS) of the low-frequency radio photons as a vulnerable source of scattering, susceptible to explaining the evolution of new components of some radio pulsars at higher bands. We couple the conventional curvature radiation (CR) mechanism and ICS, and suggest that the spectral convolution of the flux component individually from CR and the modulated template due to the ICS scattered component can be combined to reproduce such signatures associated with the diverse morphology of the integrated pulse profile. We reproduce the beam frequency diagram, the geometrical variation of different parameters of the emission geometry, as well as the multi-frequency evolution from theory. We have suitably tuned the input parameter space and given the combination of parameters that can tune to a particular scattered frequency in tabulated form. We conclude that ICS may be a responsible process for describing the emergence of new components in higher radio emission bands.

Figures (6)

• Figure 1: The Above figure shows the overall geometry of the ICS process in the pulsar magnetosphere in the form of a Cartoon diagram. Bottom line picture shows the neutron star embedded in a dipolar structure. $\hat{\Omega}$, $\hat{m}$ represent the the rotation axis and the magnetic moment. ICS process, scattered frequency $\nu_{ics}$ is proportional to the input radio frequency ($\nu_{i}$) and Lorentz factor $\gamma$ of the secondary plasma. The upper side displays a zoomed version of the neutron star, featuring the polar cap and the parameter spaces involved in the ICS geometry. $\theta_{c}$ denotes the angle between the magnetic axis and the last open field line,$\theta_{\mu}$ denotes the angle between the magnetic axis and the emitted radiation direction, and finally $\theta_{i}$ demarcates the angle between the radiation direction and the local motion of plasma particles.
• Figure 2: Figure corresponds to field line constant as a fraction of light cylinder radius vs longitude for different Lorentz factor, we have chosen $\alpha=45^{0}$, $P=0.37 ~$, $\sigma=1^{\circ}$ for the plot. The other parameters are well explained in the text.
• Figure 3: Above figure shows the last open field line constant as a fraction of light cylinder radius for $\alpha=45^{0}$, $P=0.37 ~$, $\sigma=1^{\circ}$.
• Figure 4: Above figure shows the variation of the polar angle corresponding to the last open field line with respect to rotation phase for $\alpha=45^{0}$, $P=0.37 ~$, $\sigma=1^{\circ}$.
• Figure 5: Figures (a) and (b) correspond to the beam frequency diagram for PSR B2111+46, representing the output emitted frequency vs beaming angle and emitted frequency vs emission radii, respectively. Parameter space chosen for Figures (a)-(b) are, spin period of pulsar $P=1$, Lorentz factor $\gamma_{0}=1000$, decay constant $\xi=0.16$, $R_{Ns}=10 ~Km$, input seed photon frequency $\nu_{i}=100~MHz$, dipole tilt angle $\alpha=9^{\circ}$, line of sight impact angle $\sigma=1.4^{\circ}$. Figures (c)-(d) represent the beaming diagram of PSR B1933+16 and to generate it we have chosen $P=0.37~S$, $\gamma_{0}=300$, $\xi=0.16$, $R_{Ns}=10~Km$, $\nu_{i}=1~MHz$. Rest parameters are demarcated in the diagram with a colour legend. To comply with the symbol as used in the paper by 2007AA...465..525Z, we have used $\psi$, and $\psi_{c}$ in the legend of the figure, which is equivalent to $\phi$ and $\phi_{c}$ in the current paper, implies $\psi=\phi$ denotes azimuth and $\psi_{c}=\phi_{c}$ marks the azimuthal location of the sparks.