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Preprint 02d/02

GX 301-2 - The Periastron Passage

I. Kreykenbohm (1), W. Coburn (2), J. Wilms (1), R. E. Rothschild (2), W. A. Heindl (3), P. Kretschmar (4,5), R. Staubert (1)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, 94702-7450, U.S.A.
(3) CASS, University of California, San Diego, La Jolla, CA 92093, U.S.A.
(4) INTEGRAL Science Data Center, ISDC, 1290 Versoix, Switzerland
(5) Max-Planck-Institut f\"ur extraterrestrische Physik, Giessenbachstr.~1, D-85740 Garching, Germany

in: New Visions of the X-ray Universe in the XMM-Newton and Chandra Era, eds. F. Jansen & TBD, ESA SP-488, 2002

Abstract.

We present a preliminary analysis of observations of the High Mass X-ray Binary GX 301-2 taken in 2000 November with the Rossi X-ray Timing Explorer (RXTE). The observations cover the pre-periastron flare and the periastron passage, totaling in an observation time of about 200 ksec.

X-ray light curves and pulse phase resolved spectra with high temporal resolution were obtained. Using epoch-folding we derive a pulse period of 684.4 s indicating that the pulsar continues its spin down.

Pulse Profiles in four energy bands show a remarkable variability: during the pre-periastron flare, the secondary peak vanishes almost completely below 10 keV, while it is strong outside the flare and after the periastron passage.

The X-ray spectra are difficult to model and heavily absorbed: we use a partial covering model consisting of two power-law components and an additive ionized iron line at 6.48 ± 0.03 keV. The power-laws are modified by the Fermi-Dirac cutoff and photo-electric absorption of ~20x10²² H-atoms cm^-2 for the first component, and up to ~1000x10²² H-atoms cm^-2 for the second component after the periastron passage.

At higher energies we observe a cyclotron resonant scattering feature (CRSF). The energy and the depth of the CRSF vary strongly over the pulse: the energy varies from 28 (+3/-2) keV in the pulse minimum to 36 ± 2 keV in the fall of the main pulse; the depth tau_C varies between 0.07 (+0.03/-0.04) in the pulse minimum and 0.26 (+0.06/-0.05) in the rise of the secondary pulse.

Key words: X-rays: stars - stars: magnetic fields - stars: pulsars: individual: GX 301-2

Paper (106k gzip'ed Postscript including figures)

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