Comparing geometrical and delay radio emission heights in pulsars

Abstract

Abstract. We use a set of carefully selected, published average multifrequency polarimetric observations for six bright cone−dominated pulsars and devise a method to combine the multifrequency polarization position angle (PPA) sweep traverses. We demonstrate that the PPA traverse is in excellent agreement with the rotating vector model over this broad frequency range, confirming that radio emission emanates from perfectly dipolar field lines. Correcting for the effect of retardation we firmly establish the steepest gradient point in the combined PPA traverse to be the fiducial phase in these pulsars. We use this combined curve and inputs from earlier studies to determine the geometrical angles of the neutron star, namely α -the angle between the rotation and the dipole magnetic axis and β -the angle between the magnetic axis and the observers line of sight. Using these estimates of α and β we derive the geometrical emission heights (r geo ). Further, using the relativistic beaming model based on effects of aberration and retardation, we find the delay emission heights r BCW delay suggested by Blaskiewicz et al. (1991). We find in general r BCW delay < r geo , which can be explained by a broad emission region operating in pulsars or/and the signature of the magnetic field sweepback effect as suggested by Dyks et al. (2003). For pulsars with central core emission in our sample, we find the peak of the central core component to lag behind the steepest gradient of the PPA traverse at several frequencies. Significant frequency evolution of the core width is observed over this frequency range. The above facts strongly suggest: (a) the peak core emission does not lie on the fiducial plane containing the dipole magnetic axis and the rotation axis, and (b) the core emission does not originate from the polar cap surface.

A study of multifrequency polarization pulse profiles of millisecond pulsars

“…We have shown that 18 of the 24 MSPs exhibit emission over more than half of the pulse period and the overall pulse width is relatively constant for pulsars that have high S/N profiles in all three bands. The MSPs in our sample do not show the frequency evolution of the component separations (Kramer et al 1999a) that has been observed in normal pulsars (e.g., Cordes 1978;Thorsett 1991;Mitra & Rankin 2002;Mitra & Li 2004;Chen & Wang 2014). …”

Meterwavelength Single-Pulse Polarimetric Emission Survey

“…Mitra & Deshpande 1999, Karastergiou & Johnston 2007, estimating the radio emission heights (e.g. Mitra & Li 2004, Kijak & Gil 1997 and probing the validity of the RFM (Mitra & Rankin 2002). …”

A New Model for the Beams of Radio Pulsars

“…• the maximum altitude of emission, in all pulsars, is set to ∼1000 km at a frequency of ∼1 GHz; typical maximum emission heights from the literature range from ∼10 to ∼1000 km above the stellar surface (Blaskiewicz et al 1991, Mitra & Li 2004); • the minimum altitude of emission is large for young pulsars (similar to the maximum altitude) and small (∼20 km) for older pulsars; • emission arising from discrete locations within the entire range of emission heights is possible at a given frequency; • the polarization PA of each patch is tied to the magnetic field line at the centre of that patch. Figure 1 illustrates the model which naturally reproduces virtually all the observational phenomenology outlined in section 2.…”