Single-Pulse Correlations in PSR B0329+54: Implications for Radio Emission Zones

TL;DR

This study addresses how single-pulse radio emission from PSR B0329+54 correlates across a dense, broad frequency range ($300-1460$ MHz) to probe emission-zone geometry in the pulsar magnetosphere. Using flux-calibrated and scintillation-corrected single-pulse time series from the uGMRT across $13$ subbands, the authors analyze cross-frequency correlations and maps, revealing very strong broadband correlations without anticorrelations and a peak near the central component that remains robust across frequencies. They observe that emission components move toward the midpoint with increasing frequency, and that correlations are strongest for corresponding components, implying distinct, frequency-dependent emission zones along open dipolar field lines; reproducing both the observed correlation curves and the inverted spectrum with turnover at about $470$ MHz remains a modeling challenge. The results bolster coherent curvature radiation from relativistic charge bunches as a plausible emission mechanism and demonstrate how single-pulse correlations encode underlying magnetospheric geometry, guiding future simulations of pulsar radio emission.

Abstract

Individual radio pulses from a pulsar are directly linked to the underlying emission processes and the associated magnetic field geometry within its magnetosphere. Thus, single-pulse studies across frequencies can provide crucial insights into the physics of radio emission. Multiple studies have investigated single-pulse correlations in PSR B0329+54 with widely separated discrete frequencies, reporting the broadband nature of pulsar emission. However, understanding the frequency evolution of these correlations has been limited by poor frequency sampling, and the physical origin of these correlations remains unexplored. We present a detailed study of single-pulse correlations in PSR B0329+54 at low radio frequencies using the upgraded Giant Meterwave Radio Telescope (uGMRT), with well-sampled time series spanning 300-1460 MHz. We derived an inverted flux spectrum for this pulsar, with a turnover near 470 MHz. We used flux-calibrated and scintillation-corrected single pulses to study correlations across frequencies. Our results show that maximum correlations consistently occur near the longitude of the central component, with correlation strength exceeding 69\% for all frequency combinations, while outer components exhibit correlations above 46\%. These findings indicate very strong inter-frequency correlations, with no anticorrelations detected. No cross-component correlations were observed; only corresponding components correlate across frequencies. The longitudes of maximum correlation do not coincide with the intensity peaks of the average profile. We also examine how correlations vary with frequency at selected fiducial longitudes. The observations reported in this work favor curvature radiation from relativistic charge bunches in the pulsar plasma; however, reproducing the correlation curves along with spectra remains an open challenge.

Figures (9)

• Figure 1: Flux densities of PSR B0329+54 from 300$-$1460 MHz, derived from imaging interferometric visibility data from the uGMRT. The spectrum shows a turnover at 469(8) MHz (dashed vertical line), with flux decreasing on both sides of this turnover frequency. The flux data above are fitted with a broken power law (dashed rising/declining segments), with $\alpha$ representing the spectral index of the fitted power law.
• Figure 2: Pulse-to-pulse variations of equivalent continuum flux density for $\sim$19 minutes of observation at 309, 720, and 1374 MHz. The left and right panels display data before and after scintillation correction. The dark solid black line in each plot represents the 200-second running median of the series. In the 309 MHz series, 14 out of 1594 pulses were found to be RFI contaminated, and the corresponding points in this figure have been set to zero.
• Figure 3: Correlation contour map between the 309 MHz and 483 MHz time series, along with their average profiles. The x- and y-axes represent pulse longitude in degrees.
• Figure 4: Correlation contour map between the 309 MHz and 720 MHz time series.
• Figure 5: Correlation contour map between the 309 MHz and 1374 MHz time series.