Differential frequency-dependent delay from the pulsar magnetosphere

T. E. Hassall 1 B. W. Stappers 2 P. Weltevrede 2 J. W. T. Hessels 3 A. Alexov 4 T. Coenen 4 A. Karastergiou 5 M. Kramer 2 E. F. Keane 6 V. I. Kondratiev 4 J. Van Leeuwen 3 A. Noutsos 6 M. Pilia 4 M. Serylak 7, 8 C. Sobey 6 K. Zagkouris 5 R. Fender 1 M. E. Bell 1 J. Broderick 1 J. Eislöffel 9 H. Falcke 4, 10, 11 Jean-Mathias Grießmeier 7, 8 M. Kuniyoshi 6 J. C. A. Miller-Jones 12 M. W. Wise 12, 4 O. Wucknitz 13 P. Zarka 14 A. Asgekar 4 F. Batejat 15 M. J. Bentum 4 G. Bernardi 16 P. Best 17 A. Bonafede 18 F. Breitling 19 M. Brüggen 20 H. R. Butcher 4 B. Ciardi 15 F. De Gasperin 21 J.-P. De Reijer 4 S. Duscha 4 R. A. Fallows 4 C. Ferrari 22 W. Frieswijk 4 M. A. Garrett 4, 23 A. W. Gunst 4 G. Heald 4 M. Hoeft 9 E. Juette 24 P. Maat 4 J. P. Mckean 4 M. J. Norden 4 M. Pandey-Pommier 25 R. Pizzo 4 A. G. Polatidis 4 W. Reich 6 H. Röttgering 23 J. Sluman 4 Y. Tang 4 C. Tasse 26 R. Vermeulen 4 R. J. Van Weeren 4 S. J. Wijnholds 4 S. Yatawatta 21
Abstract : Some radio pulsars show clear 'drifting subpulses', in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14-5100 MHz. Despite this, the shapes of the dn´ftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies (<500 MHz), a discrete step of ~180° in subpulse phase is observed at higher frequencies (>820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency - one driftband arriving 30 pulses earlier at 20 MHz than it does at 1380 MHz, whilst the other arrives simultaneously at all frequencies. The drifting pattern which is observed here cannot be explained by either the rotating carousel model or the surface oscillation model, and could provide new insight into the physical processes happening within the pulsar magnetosphere.
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Astronomy and Astrophysics - A&A, EDP Sciences, 2013, 552 (A61), 〈10.1051/0004-6361/201220764〉
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T. E. Hassall, B. W. Stappers, P. Weltevrede, J. W. T. Hessels, A. Alexov, et al.. Differential frequency-dependent delay from the pulsar magnetosphere. Astronomy and Astrophysics - A&A, EDP Sciences, 2013, 552 (A61), 〈10.1051/0004-6361/201220764〉. 〈insu-01288653〉



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