Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX.pdfVIP

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2017-04-11 发布于江苏
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Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX.pdf

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Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX

a r X i v : a s t r o - p h / 0 4 0 2 2 2 1 v 2 1 3 A u g 2 0 0 4 Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545 S. C?. I?nam and A. Baykal Department of Physics, Middle East Technical University, Inonu Bulvari, Balgat, Ankara 06531 Turkey scinam@metu.edu.tr, altan@astroa.physics.metu.edu.tr J. Swank NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA swank@xenos.gsfc.nasa.gov and M.J.Stark Department of Physics, Lafayette College, Easton, PA 18042 USA starkm@lafayette.edu ABSTRACT XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and January 29, 2003, the spin period and average spin-up rate during the XMM- Newton observations were found to be 354.7940±0.0008 s and (7.4±0.9)×10?13Hz s?1 respectively. In the power spectrum of the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around 0.044 Hz (22.7 s) with an rms fractional amplitude ～6.6 %. We interpreted this QPO feature as the Keplerian motion of inhomogenuities through the inner disk. In the X-ray spectrum, in addition to the power law component with high energy cutoff and ～ 6.4 keV fluorescent iron emission line (Baykal et al., 2002), we discovered a soft component consistent with a blackbody emission with kT ～ 1.9keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius ～ 0.3 km, suggesting the polar cap on the neutron star surface as the source of blackbody emission. The flux of the iron emission line at ～ 6.42 keV was shown to peak at the off-pulse phase, supporting the idea that – 2 – this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap. Subject headings: stars: individual (SAX J2103.5+4545) — stars: neutron — X-rays: binaries — X-ra