Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations

T. E. Hassall 1 B. W. Stappers 1 J. W. T. Hessels 2 M. Kramer 1, 3 A. Alexov 2 K. Anderson 2 T. Coenen 2 A. Karastergiou 4 E. F. Keane 3 V. I. Kondratiev 2 K. Lazaridis 3 J. van Leeuwen 2 A. Noutsos 3 M. Serylak 5, 6 C. Sobey 3 J. P. W. Verbiest 3 P. Weltevrede 1 K. Zagkouris 4 R. Fender 7 R. A. M. J. Wijers 8 L. Bahren 8 M. E. Bell 7 J. W. Broderick 7 Stéphane Corbel 9, 5 E. J. Daw 10 V. S. Dhillon 10 J. Eisloffel 11 H. Falcke 3 Jean-Mathias Grießmeier 6 P. Jonker 12 C. Law 8 S. Markoff 8 J. C. A. Miller-Jones 8 R. Osten 13 E. Rol 8 A. M. M. Scaife 14 B. Scheers 8 P. Schellart 12 H. Spreeuw 8 J. Swinbank 8 S. ter Veen 12 M. W. Wise 2, 8 R. Wijnands 8 O. Wucknitz 15 P. Zarka 16 A. Asgekar 2 M. R. Bell 17 M. J. Bentum 2 G. Bernardi 18 P. Best 19 A. Bonafede 20 A. J. Boonstra 2 M. Brentjens 2 W. N. Brouw 21 M. Bruggen 20 H. R. Butcher 2 B. Ciardi 17 M. A. Garrett 2, 22 M. Gerbers 2 A. W. Gunst 2 M. P. van Haarlem 2 G. Heald 2 M. Hoeft 11 H. Holties 2 A. de Jong 2 L. V. E. Koopmans 21 M. Kuniyoshi 3 G. Kuper 2 G. M. Loose 2 P. Maat 2 J. Masters 23 J. P. Mckean 2 H. Meulman 2 M. Mevius 2 H. Munk 2 J. E. Noordam 2 E. Orru 24 H. Paas 2 M. Pandey-Pommier 25 V. N. Pandey 2 R. Pizzo 2 A. Polatidis 2 W. Reich 3 H. Rottgering 22 J. Sluman 2 M. Steinmetz 26 C. G. M. Sterks 27 Michel Tagger 6 Y. Tang 2 C. Tasse 28, 29 R. Vermeulen 2 R. J. van Weeren 2 S. J. Wijnholds 2 S. Yatawatta 21
Abstract : Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40-190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these observations which show that the dispersion law is accurate to better than 1 part in 100000 across our observing band. We use this fact to constrain some of the properties of the ISM along the line-of-sight and use the lack of any aberration or retardation effects to determine upper limits on emission heights in the pulsar magnetosphere. We also discuss the effect of pulse profile evolution on our observations, and the implications that it could have for precision pulsar timing projects such as the detection of gravitational waves with pulsar timing arrays.
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T. E. Hassall, B. W. Stappers, J. W. T. Hessels, M. Kramer, A. Alexov, et al.. Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations. Astronomy and Astrophysics - A&A, EDP Sciences, 2012, 543, A66 (20 p.). ⟨10.1051/0004-6361/201218970⟩. ⟨insu-01253922⟩

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