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Astron. Astrophys. 321, 513-518 (1997)

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Unexpected variations in pulsar flux-densities at mm-wavelengths

M. Kramer 1, K.M. Xilouris 2 and B. Rickett 3

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 National Astronomy and Ionospheric Center, Arecibo Observatory, P.O. Box 995, Arecibo, Puerto Rico 00613
3 Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093-0407, USA

Received 8 July 1996 / Accepted 29 October 1996

Abstract

Monitoring of the flux-densities near 30 GHz are reported for four pulsars. Statistically significant variations apparently random in nature are found over 10 to 20 minutes, with rms amplitudes 20% to 100% of the mean flux. These fluctuations are substantially above the predictions for interstellar scintillation at these high frequencies. The observations presented here comprise the first attempt towards understanding the effects of the ISM on pulsar signals at such high frequencies, a spectral region where very little is known about the behaviour of pulsars or the ISM. When extrapolated from observations at lower frequencies, the four pulsars should exhibit very weak interstellar scintillation, with rms modulation indices from 2% to 14%. The fluctuations therefore are attributed rather to intrinsic variation of the pulsar emission at these frequencies.

Key words: pulsars: general – pulsars: individual: B0329+54, B0355+54, B1929+10, B2021+51 – ISM: general – radiation mechanisms: miscellaneous

Send offprint requests to: M. Kramer (mkramer@mpifr-bonn.mpg.de)

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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