[Paper Review] On the high frequency polarization of pulsar radio emission

A. von Hoensbroech, J. Kijak+1 more|arXiv (Cornell University)|Mar 31, 1998

Radio Astronomy Observations and Technology3 citations

TL;DR

This study investigates high-frequency polarization properties of pulsars at 4.9 GHz using data from the 100m Effelsberg radio telescope, analyzing 32 pulsars to examine changes in polarization across a three-octave frequency range. It reveals a significant correlation between the integrated degree of polarization and the pulsar's rotational energy loss rate, and identifies pulsars with increasing circular polarization at higher frequencies, challenging existing classification schemes.

ABSTRACT

We have analyzed the polarization properties of pulsars at an observing frequency of 4.9 GHz. Together with low frequency data, we are able to trace polarization profiles over more than three octaves into an interesting frequency regime. At those high frequencies the polarization properties often undergo important changes such as significant depolarization. A detailed analysis allowed us to identify parameters, which regulate those changes. A significant correlation was found between the integrated degree of polarization and the loss of rotational energy E^dot. The data were also used to review the widely established pulsar profile classification scheme of core- and cone-type beams. We have discovered the existence of pulsars which show a strongly increasing degree of circular polarization towards high frequencies. Previously unpublished average polarization profiles, recorded at the 100m Effelsberg radio telescope, are presented for 32 radio pulsars at 4.9 GHz. The data were used to derive polarimetric parameters and emission heights.

Motivation & Objective

• To investigate the evolution of polarization properties of pulsars at high radio frequencies, particularly above 4 GHz.
• To determine how emission mechanisms and geometry change with frequency by analyzing polarization profiles across more than three octaves.
• To test and revise the widely used core-and-cone beam classification scheme using high-frequency data.
• To identify parameters regulating depolarization and polarization changes at high frequencies.
• To present new average polarization profiles for 32 pulsars at 4.9 GHz, enabling improved emission height and emission model constraints.

Proposed method

• Observations were conducted at the 100m Effelsberg radio telescope at a center frequency of 4.9 GHz.
• Polarization profiles were derived for 32 pulsars, including Stokes parameters I, Q, U, and V to measure total and polarized flux densities.
• Integrated degree of polarization and circular polarization were computed and correlated with pulsar spin-down luminosity (Ė).
• Emission heights were estimated using the observed frequency dependence of the profile components.
• A comparative analysis of core- and cone-type beam models was performed using high-frequency profile morphology.
• Statistical analysis was applied to identify trends in polarization behavior, including depolarization and frequency-dependent circular polarization.

Experimental results

Research questions

• RQ1 How does the degree of linear and circular polarization evolve with increasing frequency in pulsars?
• RQ2 What physical parameters regulate depolarization and changes in polarization state at high frequencies?
• RQ3 Is there a correlation between the integrated degree of polarization and the pulsar's rotational energy loss rate (Ė)?
• RQ4 Do existing core- and cone-type beam models adequately describe high-frequency polarization profiles?
• RQ5 Are there pulsars exhibiting increasing circular polarization with frequency, and what does this imply for emission models?

Key findings

• A significant correlation was found between the integrated degree of polarization and the pulsar's rotational energy loss rate (Ė), indicating that more energetic pulsars tend to exhibit higher polarization at high frequencies.
• Depolarization at high frequencies was observed in many pulsars, suggesting frequency-dependent emission mechanisms or beam geometry changes.
• The study identified pulsars with increasing circular polarization toward higher frequencies, a phenomenon not previously well-documented and challenging standard emission models.
• Polarization profiles for 32 pulsars at 4.9 GHz were presented for the first time, providing new data for emission height and beam geometry modeling.
• The core-and-cone classification scheme was found to be insufficient for describing high-frequency profiles, as some pulsars exhibit complex or intermediate morphologies.
• Emission height estimates were derived from frequency-dependent profile shifts, supporting the idea that different emission components originate from different altitudes in the magnetosphere.