Pulsar polarisation below 200 MHz: Average profiles and propagation effects

A. Noutsos C. Sobey V. I. Kondratiev 1 P. Weltevrede 2 J. P. W. Verbiest 3, 4 A. Karastergiou M. Kramer 4, 2 M. Kuniyoshi A. Alexov R. P. Breton A. V. Bilous 5 S. Cooper 6 H. Falcke 5, 1 Jean-Mathias Grießmeier 7, 8 T. E. Hassall 9 J. W. T. Hessels 1 E. F. Keane 10 S. Osłowski M. Pilia 1 M. Serylak 11 B. W. Stappers 2 S. Ter Veen J. Van Leeuwen K. Zagkouris K. Anderson 12 L. Bähren M. Bell J. Broderick 13, 14 D. Carbone 15 Y. Cendes 15 T. Coenen Stéphane Corbel 16, 8 J. Eislöffel 17 R. Fender 18 H. Garsden 16 P. Jonker C. Law S. Marko J. Masters 19 J. Miller-Jones G. Molenaar 15 R. Osten M. Pietka E. Rol 15 A. Rowlinson B. Scheers 15 H. Spreeuw T. Staley A. Stewart 20 J. Swinbank 21, 15 R. Wijers 15 R. Wijnands 15 M. Wise P. Zarka 22 A. Van Der Horst 15
Abstract : We present the highest-quality polarisation profiles to date of 16 non-recycled pulsars and four millisecond pulsars, observed below 200 MHz with the LOFAR high-band antennas. Based on the observed profiles, we perform an initial investigation of expected observational effects resulting from the propagation of polarised emission in the pulsar magnetosphere and the interstellar medium. The predictions of magnetospheric birefringence in pulsars have been tested using spectra of the pulse width and fractional polarisation from multifrequency data. The derived spectra offer only partial support for the expected effects of birefringence on the polarisation properties, with only about half of our sample being consistent with the model's predictions. It is noted that for some pulsars these measurements are contaminated by the effects of interstellar scattering. For a number of pulsars in our sample, we have observed significant variations in the amount of Faraday rotation as a function of pulse phase, which is possibly an artefact of scattering. These variations are typically two orders of magnitude smaller than that observed at 1400 MHz by Noutsos et al. (2009), for a different sample of southern pulsars. In this paper we present a possible explanation for the difference in magnitude of this effect between the two frequencies, based on scattering. Finally, we have estimated the magnetospheric emission heights of low-frequency radiation from four pulsars, based on the phase lags between the flux-density and the PA profiles, and the theoretical framework of Blaskiewicz, Cordes & Wasserman (1991). These estimates yielded heights of a few hundred km; at least for PSR B1133+16, this is consistent with emission heights derived based on radius-to-frequency mapping, but is up to a few times larger than the recent upper limit based on pulsar timing.
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A. Noutsos, C. Sobey, V. I. Kondratiev, P. Weltevrede, J. P. W. Verbiest, et al.. Pulsar polarisation below 200 MHz: Average profiles and propagation effects. Astronomy and Astrophysics - A&A, EDP Sciences, 2015, 576 (A62), 27 p. ⟨10.1051/0004-6361/201425186⟩. ⟨insu-01182209⟩

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