Institut für Astronomie und Astrophysik Abteilung Astronomie Sand 1, D-72076 Tübingen, Germany
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Preprint 07/04

The variable cyclotron line in GX 301-2

Ingo Kreykenbohm (1,2), Jörn Wilms (3), Wayne Coburn (4), Markus Kuster (5), Richard E. Rothschild (6), William A. Heindl (6), Peter Kretschmar (5,2), Rüdiger Staubert (1)

(1) Institut für Astronomie und Astrophysik - Astronomie, Sand 1, 72076 Tübingen, Germany
(2) Integral Science Data Centre, Chemin d'Écogia 16, 1290 Versoix, Switzerland
(3) Department of Physics, University of Warwick, Coventry CV4 7AL, U.K.
(4) Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA, 94702-7450, USA
(5) Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, D-85740 Garching, Germany
(6) Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA, 92093-0424, USA

To be published in: A&A

Abstract. We present pulse phase resolved spectra of the hypergiant high mass X-ray binary GX 301-2. We observed the source in 2001 October with RXTE continuously for a total on-source time of almost 200ksec. We model the continuum with both, a heavily absorbed partial covering model and a reflection model. In either case we find that the well known cyclotron resonant scattering feature (CRSF) at 35keV is - although present at all pulse phases - strongly variable over the pulse: the line position varies by 25% from 30keV in the fall of the secondary pulse to 38keV in the fall of the main pulse where it is deepest. The line variability implies that we are seeing regions of magnetic field strength varying between 3.4 10¹²G and 4.2 10¹²G.
 
Key words: X-rays: stars - stars: magnetic fields - stars: pulsars: individual: GX 301-2

Preprint (363 kb PDF file including figures)
Astrophysics (astro-ph): astro-ph/0409015

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