Pulsar B1237+25 Aberration/Retardation Analysis from Decimeter to Decameter Wavelength: Challenge to "Radius-to-Frequency Mapping"

TL;DR

This paper presents a broad-band A/R analysis of PSR B1237+25, combining multi-observatory profiles from decametric to GHz frequencies to estimate emission heights and test radius-to-frequency mapping. Using the core component as a fiducial longitude and Gaussian decomposition of core/cone emission, the authors find emission heights in the $\sim$200–$400$ km range for both inner and outer cones with little frequency dependence, challenging the standard radius-to-frequency mapping paradigm. They show that the core center coincides with the PPA inflection and Stokes $V$ zero-crossing across bands, enabling reliable A/R measurements, while highlighting that propagation and mode physics likely shape the observed broad-band profile evolution rather than height changes alone. The results imply a common emission region across frequencies and motivate reconsideration of core radiation mechanisms and magnetospheric propagation effects in pulsar radio emission models.

Abstract

PSR B1237+25 is perhaps the canonical example of a pulsar with a core/double cone profile. Moreover, it is bright with little spectral turnover, and its profile perhaps uniquely remains undistorted by scattering far into the decametric band. Here we assemble more than a dozen of the highest quality profiles (30 MHz to 5 GHz) from half a dozen observatories, where possible polarimetric. The pulsar's 2.6$^{\circ}$ core component marks the magnetic axis longitude, and we confirm that this point coincides both with the linear polarization angle inflection point and the zero-crossing of its antisymmetric circular signature -- thus providing the possibility to estimate emission heights over a very broad band using aberration/retardation (A/R). We then carefully fit the profile components with Gaussians to identify and study the subtle asymmetries produced by A/R. We find a consistent A/R in the pulsar's profiles of some 0.5$^{\circ}$ longitude or 2 ms -- corresponding to a putative conal emission height of 200-400 km -- with a formal error of about 100 km. Our analysis finds no evidence whatsoever for an emission height increase with wavelength, the so-called ``radius-to-frequency mapping''. Nor do we find any significant difference in A/R effect between the outer and inner cones.

Figures (27)

• Figure 1: Broad band 16.5-33 MHz, full period B1237+25 profile from the Ukrainian UTR-2 telescope on 2021 November 24.
• Figure 2: Time-aligned Arecibo profiles of pulsar B1237+25 from hankins2010. Here we see the evolution from the high frequency "boxy" form in which the weak core is not visible to the triple outer-conal form at low frequencies. Note that the 49.2-MHz profile is broadened by a poorer time resolution.
• Figure 3: Three B1237+25 profiles (Paper I): a) a typical 327-MHz total profile; b) flare-normal mode profile; and c) quiet-normal mode profile without core emission. Note that the core component center as marked by its antisymmetric $V$ in panel b coincides with the inflection point of the PPA traverse in panel c within 0.1. Here, the total power $I$, linear $L$ and circular $V$ polarization is plotted with solid, dashed and dotted curves in the upper panel and the PPA traverse in the lower panel. The 2-$\sigma$ off-pulse RMS bar at --10 is hardly visible because it is so small.
• Figure 4: Polarimetric average profile of pulsar B1237+25 at 151 MHz from LOFAR Noutsos2015. This figure can be compared to Fig. \ref{['fig3']}, Which shows very similar features. Left panels: The total profile with $I$, $L$ and $V$ shown as solid, dashed and dotted curves in the top panel. The resolution and off-pulse noise level (although so small that to be barely visible) is shown by the boxes in the top-right corner. The PPA traverse is shown in the bottom panel. Middle panels: Profile averaging 5-second long sub-integrations with strong core emission. Right panels: Profile with weak core emission. The PPA is only plotted when $L > 2\sigma$.
• Figure 5: Upper panels: Simultaneous polarimetric observations at 70-, 50-, and 30-MHz with NenuFAR. Solid black line: total intensity $I$. Dashed green and dotted magenta lines: $L$ and $V$. Note that each frequency shows a core component with a stronger trailing portion and that the core becomes ever more depolarized at low frequency. The resolution and off-pulse noise level are shown by the small boxes at --20, and the PPA gaps occur due to regions where $L < 2\sigma$. Lower panels: NenuFAR 50-MHz flare- and quiet normal profiles as in Figs. \ref{['fig3']} and \ref{['fig4']}.