Pulsar B1237+25 at 111~MHz: average profile, mode switching, nullings, microstructure
M. V. Popov, T. V. Smirnova
TL;DR
This study analyzes PSR B1237+25 at 111 MHz with high time resolution to elucidate its emission geometry and mode-switching behavior. Using dispersion-corrected data and Gaussian decomposition of the mean profile, it identifies two central X-mode components and a single O-mode cone for the outer/inner components, with emission heights of $R_{X}\approx80~\mathrm{km}$ and $R_{out}\approx370~\mathrm{km}$. A newly detected narrow central component and submicrosecond microstructure ($τ_μ\le0.5~μs$) support a polar-gap spark model, yielding a vacuum gap height $h_p\le750~\mathrm{cm}$ and a Lorentz factor bound $\gamma\ge260$. The analysis shows mode-dependent drift and nulling patterns, with $P_3=2.7P_1$ drift visible only in the QN, and an AB mode representing a reorganized activity-zone configuration; the observed radius-frequency scaling follows a power law with exponent $α\approx-0.16$ for both cones, consistent with hollow-cone O-mode dynamics. Overall, the results reinforce a two-cone plus core geometry with distinct O-mode and X-mode emission, offer emission-height estimates at low frequency, and demonstrate broadband nulling and mode-switching behavior tied to polar-cap discharge processes.
Abstract
The observations of B1237+25 at a frequency of 111 MHz were analyzed. For the first time in the normal radiation mode a new component in the central region in the average profile was detected. This component is manifested in all modes of pulsar emission: quiet-normal (QN), flare-normal (FN) and in the abnormal mode (AB). The subpulse drift is observed in the QN mode only in the first and last components of the average profile. The normal mode is interrupted by nullings and transitions into the abnormal AB mode. In the AB mode, the structure at the edge of the outer cone is destroyed, the distance between the inner and outer cones is almost doubled, and the distance between the inner cone and the central region is reduced.Analysis of our data has shown that the components of the outer and inner cones of the average profile are formed by an ordinary mode of radio emission (O-mode) and form a single cone radiation of the pulsar. The central components of the average profile (wide and narrow) are formed by an extraordinary mode (X-mode). Estimates of the height of the radiation output from the central region (X-mode) and the cone radiation (O-mode) are obtained: 80~km and 370~km, respectively. A microstructure with a time scale of $τ_μ\le0.5$~$μs$ has been detected. This time scale corresponds well to the time of the development of a spark discharge in the polar cap. For this value $τ_μ$, the height of the vacuum gap should be $h_p\le750$~cm. Based on the steepness of the individual pulse's trailing edge at the longitude of the first component, a limit was obtained on the value of the $γ$ factor of the relativistic secondary plasma: $γ\ge$260. The dependence of the distance between the components of the outer and inner cone of radiation on the frequency is the same and corresponds to a power law with an exponent of -0.16.