Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733611r&link_type=abstract
American Astronomical Society, AAS Meeting #217, #336.11; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Lyne & Manchester (1988) identified a group of some 50 pulsars they called ``partial cones'' which they found difficult to classify and interpret. They were notable for their asymmetric average profiles and asymmetric polarization position-angle (PPA) traverses, wherein the steepest gradient (SG) point fell toward one edge of the total intensity profile. Over the last two decades, this population of pulsars has raised cautions regarding the core/cone model of the radio pulsar-emission beam which implies a high degree of order, symmetry and geometric regularity.
We reinvestigate this population ``partial cone'' pulsars on the basis of new single pulse polarimetric observations of 39 of them, observed with the Giant Meterwave Radio Telescope in India and the Arecibo Observatory in Puerto Rico. These highly sensitive observations help us to establish that most of these ``partial cones'' exhibit a core/cone structure just as did the ``normal'' pulsars studied earlier. In short, we find that many of these ``partial cones'' are partial in the sense that the emission above different areas of their polar caps can be (highly) asymmetric. However, when studied closely we find that their emission geometries are overall identical to core/double cone structure encountered earlier---that is, with specific conal dimensions scaling as the polar cap size.
Further, the ``partial cone'' population includes a number of stars with conal single profiles that are asymmetric at meter wavelengths for unknown reasons (e.g., like those of B0809+74 or B0943+10). We find that aberration-retardation appears to play a significant role in distorting the core/cone emission-beam structure in rapidly
rotating pulsars. We also find several additional examples of highly polarized pre- and postcursor features that do not appear to be generated at low altitude but rather at high altitude, far from the usual polar fluxtube emission sites of the core and conal radiation.
Mitra David
Rankin Joanna M.
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