Broad band X-ray spectrum of KS 1947+300 with BeppoSAX

We present results obtained from three BeppoSAX observations of the accretion-powered transient X-ray pulsar KS 1947+300 carried out during the declining phase of its 2000 November – 2001 June outburst. A detailed spectral study of KS 1947+300 across a wide X-ray band (0.1–100.0 keV) is attempted for the first time here. Timing analysis of the data clearly shows a 18.7 s pulsation in the X-ray light curves in the above energy band. The pulse profile of KS 1947+300 is characterized by a broad peak with sharp rise followed by a narrow dip. The dip in the pulse profile shows a very strong energy dependence. Broad-band pulse-phase-averaged spectroscopy obtained with three of the BeppoSAX instruments shows that the energy spectrum in the 0.1–100 keV energy band has three components, a Comptonized component, a ∼ 0.6 keV blackbody component, and a narrow and weak iron emission line at 6.7 keV with a low column density of material in the line of sight. We place an upper limit on the equivalent width of the iron Kα line at 6.4 keV of ∼ 13 eV (for a width of 100 eV). Assuming a spherical blackbody emitting region and the distance of the source to be 10 kpc, the radius of the emitting region is found to be in the range of 14–22 km, which rules out the inner accretion disk as the soft X-ray emitting region. Subject headings: stars: neutronPulsars: individual: KS 1947+300 -X-rays: stars Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan, [email protected], [email protected] Department of Physics, University College Cork, Cork, Ireland, [email protected] Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India, [email protected]