[Paper Review] The Mode Switching in Pulsar J1326$-$6700

Z. G. Wen, W. M. Yan+8 more|arXiv (Cornell University)|Nov 11, 2020

Pulsars and Gravitational Waves Research26 references4 citations

TL;DR

This study analyzes mode switching in pulsar J1326$-$6700 using 1369 MHz data from the Parkes 64-m telescope, revealing that the abnormal mode features weaker central/trailing emission, a leading component shifted 2° earlier, and emission from a higher altitude (3× greater than normal mode). The abnormal mode lasts <1 minute, occurs 15% of the time, and exhibits quasi-periodic switching with Weibull-distributed timescales, suggesting memory in the switching process and a possible jump in emission height due to changes in the magnetospheric gap height.

ABSTRACT

We report on a detailed study of the mode switching in pulsar J1326$-$6700 by analyzing the data acquired from the Parkes 64 m radio telescope at 1369 MHz. During the abnormal mode, the emission at the central and trailing components becomes extremely weak. Meanwhile, the leading emission shifts toward earlier longitude by almost 2°, and remains in this position for typically less than a minute. The mean flux density of the normal mode is almost five times that of the abnormal mode. Our data show that, for PSR J1326$-$6700, 85% of the time was spent in the normal mode and 15% was in the abnormal mode. The intrinsic distributions of mode timescales can be well described by Weibull distributions, which present a certain amount of memory in mode switching. Furthermore, a quasiperiodicity has been identified in the mode switching in pulsar J1326$-$6700. The estimated delay emission heights based on the kinematical effects indicate that the abnormal mode may have originated from higher altitude than the normal mode.

Motivation & Objective

• To investigate the physical mechanisms behind mode switching in pulsar J1326$-$6700, particularly the observed shift in emission profile and intensity changes.
• To determine the emission height difference between normal and abnormal modes using phase lags and delay-radius relations.
• To analyze the statistical distribution of mode durations and test for memory effects or periodicity in switching behavior.
• To explore the implications of the observed emission geometry for emission models, especially those involving changes in the magnetospheric gap height.
• To assess whether the observed mode switching can be explained by changes in emission altitude or beam geometry.

Proposed method

• Analysis of full-Stokes, 512-channel, 256 MHz bandwidth data from the Parkes 64-m telescope at 1369 MHz, with 256 μs integration time and 8-bit quantization.
• Use of system equivalent flux density (SEFD) calibration via observations of the unpolarized calibrator 3C218 (43.1 Jy at 1400 MHz).
• Calculation of Δχ² distributions to distinguish between normal and abnormal emission modes based on profile stability and intensity.
• Application of the relativistic beaming model using aberration and retardation effects to estimate emission height from phase lags between the profile midpoint and steepest PA gradient.
• Fitting of mode duration distributions to Weibull distributions to assess memory effects and clustering in switching behavior.
• Estimation of emission height using the delay-radius relation, comparing normal and abnormal modes via observed phase lags.

Figure 1: Top-left panel: longitude-time diagram showing intensity variations for 2000 individual pulses from PSR J1326 $-$ 6700. Time extends from left to right through pulses and successive pulses are plotted from bottom to top. Bottom-left panel: the comparisons of the mean pulse profile for the

Experimental results

Research questions

• RQ1 What are the distinct profile characteristics of the normal and abnormal emission modes in PSR J1326$-$6700?
• RQ2 How does the emission height differ between the normal and abnormal modes, and what physical mechanism could explain this difference?
• RQ3 Is there a statistical memory or periodicity in the mode switching behavior, and how is it distributed in time?
• RQ4 Why does the leading component shift earlier by ~2° during the abnormal mode, and what does this imply about emission beam geometry?
• RQ5 Can the observed mode switching be explained by changes in the magnetospheric gap height, as predicted by the vacuum gap model?

Key findings

• The normal mode accounts for 85% of the observation time, while the abnormal mode occurs for 15% of the time.
• The mean flux density of the normal mode is nearly five times that of the abnormal mode, indicating a significant intensity difference.
• The abnormal mode features a leading component shifted by approximately 2° earlier, persisting for less than a minute.
• The duration of both modes follows a Weibull distribution with shape parameters less than 1, indicating clustering and memory in the switching process.
• A quasi-periodicity in mode switching is identified, suggesting a potential underlying periodic modulation mechanism.
• Emission height estimates from phase lags indicate the abnormal mode originates at approximately three times the altitude of the normal mode, corresponding to a jump from 0.015 to 0.04 light cylinder radii.

Figure 2: Pulse energy distributions for the on-pulse (black solid histogram) and off-pulse (magenta dashed histogram) regions are calculated from all observations. The energies are normalized by their respective mean on-pulse energies. The blue solid line represents the fitting for the on-pulse ene