The main-interpulse interaction of PSR B1702–19

Abstract

Aims. This paper reports on single-pulse radio observations of PSR B1702-19 and their implications for pulsar emission theories. Methods. These observations were made with the Westerbork Synthesis Radio Telescope at 1380 and 328 MHz. The PA-swing is used to constrain possible geometries of the pulsar and the single-pulse data is analysed for subpulse modulation correlations between the main pulse and interpulse. Results. We confirm earlier conclusions that the dipole axis of this pulsar is almost perpendicular to its rotation axis, and report that both its main pulse and interpulse are modulated with a periodicity around 10.4 times the pulsar's rotation. Allowing for the half-period delay between main pulse and interpulse the modulation is found to be precisely in phase. Despite small secular variations in the periodicity, the phase-locking continues over all timescales ranging up to several years. Conclusions. The precision of the phase locking is difficult for current emission theories to explain if the main pulse and interpulse originate from opposing magnetic poles. We therefore also explore the possibility of a bidirectional model, in which all the modulated emission comes from one pole, but is seen from two sides and slightly displaced by aberration and time-delay. In this model the unmodulated emission is directed to us from the opposite pole, requiring the emission of the main pulse to originate from two different poles. This is difficult to reconcile with the observed smooth PA-swing. Whichever model turns out to be correct, the answer will have important implications for emission theories.Key words. stars: pulsars: individual: PSR B1702-19 -stars: pulsars: general -radiation mechanisms: non-thermal IntroductionThe radio pulsar B1702-19 was discovered by Manchester et al. (1978) in the second Molonglo Survey. With a period of 0.3 s, a characteristic age of 1.1 Myr and inferred surface magnetic field 1.1 × 10 12 Gauss, the pulsar was in no way unusual. However, some ten years later it was found to have an interpulse located some 180 • from the main pulse (Biggs et al. 1988), an unusual feature among pulsars, and one which has the potential for testing magnetosphere and emission models.Radio pulsars have narrow emission beams, so that an interpulse (henceforth IP) located close to 180 • from the main pulse (henceforth MP) might naturally be interpreted as a view of a second magnetic pole. Previous studies of PSR B1702-19 have tended to support this view. For example, according to Biggs et al. (1988), there is little evidence for the MP-IP separation (given as 181 • ± 1 • ) to evolve with frequency. Further support is given by the analyses of the shape of the polarisation position angle swing in and Kuzmin (1989), which is more recently confirmed by van Ommen et al. (1997). However, geometric models exist (e.g. Gil 1985;Dyks et al. 2005b) in which even a separation of this magnitude can arise from a single pole.The structure of the MP is essentially double-peaked at all frequencies, the leading pe...

Six faint gamma-ray pulsars seen with theFermiLarge Area Telescope

“…We thus find ζ < 60 • , and the Atlas then favors even larger α values. That is, J1705−1906 appears confirmed as an orthogonal rotator, supporting the two-pole and the bidirectional scenarios discussed by Weltevrede et al (2007).…”

“…However, a "kink" in the PPA swing of J1705−1906's interpulse is incompatible with simple models. The kink is examined by Weltevrede et al (2007), along with a wealth of other radio observations showing, for example, that the two radio emission regions are physically connected. Of the three distinct scenarios they propose, none explain all of the data.…”

TMRT Observations of 26 Pulsars at 8.6 GHz

“…The observed polarisation variations can be interpreted in terms of an orthogonal rotator with the main pulse and interpulse from opposite poles (e.g., Karastergiou & Johnston 2004). However, Weltevrede et al (2007) find a 10P modulation in both the main pulse and interpulse that remains phase-locked over years, a result that is difficult to explain in the two-pole model.…”

Pulsar bi-drifting: implications for polar cap geometry

“…In most pulsars which exhibit subpulse drift the observed sense is always in the same direction in a given pulsar (Weltevrede et al 2006(Weltevrede et al , 2007a. Exceptionally, examples have been found (e.g.…”