Institut für Astronomie und Astrophysik

Abteilung Astronomie

Preprint 11d/98

STABILITY OF CYCLOTRON LINE IN HER X­1

D.E. Gruber (1) , W.A. Heindl (1) , R.E. Rothschild (1) , R. Staubert (2) , J. Wilms (2) , D.M.Scott (3)

(1) Center for Astrophysics and Space Science, UCSD, La Jolla CA, USA
(2) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(3) Marshall Space Flight Center, Huntsville, AL, USA

3rd Integral Symposium - The Extreme Universe, in press

Abstract. Four observations now of Her X­1 from RXTE show steadiness of the cyclotron line centroid which limits variability to about one percent, which is well less than the 10 percent variability characteristic of the other spectral parameters. This confines the average height of scattering above the polar cap to within 35 meters, and is consistent with models which put the radiating structure within meters of the surface of the neutron star. But in other pulsars observed line centroid changes have been correlated with luminosity changes, and if interpreted as variability of the height at which scattering takes place, hundreds of meters are required. These RXTE data are not yet in conflict with such an extended radiating structure.

Key words: x­rays; neutron stars; cyclotron lines; magnetic fields

Paper (52k gzip'ed Postscript including figures)

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Jürgen Barnstedt (barnstedt AT astro.uni-tuebingen.de) Last updated 11-Dec-1998