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Preprint 13f/99

RXTE Studies of Cyclotron Lines in Accreting Pulsars

W.A. Heindl (1), W. Coburn (1), D.E. Gruber (1), M. Pelling (1), R.E. Rothschild (1), P. Kretschmar (2;3), I. Kreykenbohm (2), J. Wilms (2), K. Pottschmidt (2), and R. Staubert (2)

(1) Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, CA, 92093, USA
(2) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany
(3) INTEGRAL Science Data Centre, Ch. d'Ecogia 16, 1290 Versoix, Switzerland

To appear in: Proc. of the 5th Compton Symposium, ed. M. McConnell

Abstract. Cyclotron lines in accreting X­ray pulsar spectra result from the resonant scatter­ ing of X­rays by electrons in Landau orbits on the intense (~10¹²G) magnetic fields near the neutron star poles. For this reason they are known as cyclotron resonance scattering features (CRSFs). Because Landau transition energies are proportional to field strength (E_cyc = 12 keV approximately corresponds to B = 10¹²G), CRSF energies give us our most direct measures of neutron star magnetic fields. Other line properties, such as depths, widths, and presence of multiple harmonics, are strongly dependent on the details of the geometry and environment at the base of the accretion column. CRSFs therefore give us a sensitive (if difficult to interpret) diagnostic of the accretion region.
In this paper, we summarize the RXTE measurements of CRSFs in 8 accreting pulsars. The wide bandpass and modest resolution of the RXTE instruments make them ideal for measuring these generally broad features. In particular, the high energy response of HEXTE provides a window for discovery of new lines not detectable with proportional counters such as Ginga or the PCA alone.

Some highlights of this work are:

• New lines in the well known pulsars Cen X­3 and 4U 1626­67.
• The discovery of more than two cyclotron line harmonics in 4U 0115+63.
• The RXTE picture of the correlation between cyclotron line energy and width.

Key words: -

Paper (141k gzip'ed Postscript including figures)

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