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Preprint A/01

Discovery of a Cyclotron Resonant Scattering Feature in the RXTE Spectrum of 4U 0352+309 (X Per)

W. Coburn (1), W. A. Heindl (1), D. E. Gruber (1), R. E. Rothschild (1), R. Staubert (2), J. Wilms (2), I. Kreykenbohm (2)

(1) Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, CA 92093-0424, USA
(2) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

2001, ApJ 552, 738-747

Abstract. We have discovered a ~29 keV Cyclotron Resonant Scattering Feature (CRSF) in the X-Ray spectrum of 4U 0352+309 (X Per) using observations taken with the Rossi X-Ray Timing Explorer. 4U 0352+309 is a persistent low luminosity (L_x = 4.2x10³⁴ ergs/s) X-ray pulsar, with a 837 s period and which accretes material from the Be star X Per. The X-Ray spectrum, unusual when compared to brighter accreting pulsars, may be due to the low mass accretion rate and could be typical of the new class of persistent low luminosity Be/X-Ray binary pulsars. We attempted spectral fits with continuum models used historically for 4U 0352+309, and found that all were improved by the addition of a CRSF at ~29 keV. The model that best fit the observations is a combination of a 1.45+/-0.02 keV blackbody with a 5.4x10⁸ cm² area, and a power-law with a 1.83+/-0.03 photon index modified by the CRSF. In these fits the CRSF energy is 28.6+1.5-1.7 keV, implying a magnetic field strength of 2.5(1+z)x10¹² G in the scattering region (where z is the gravitational redshift). Phase resolved analysis shows that the blackbody and cyclotron line energies are consistent with being constant through the pulse.

Key words: stars: individual (4U 0352+309) - stars: individual (X Per) - stars: magnetic fields - stars: neutron - X-rays: stars

Paper (118k gzip'ed Postscript including figures)

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