BeppoSAX observations of the accretion-powered X-ray pulsar SMC X-1

¹ Department of Physics, University College Cork, Cork, Ireland
² Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, India

Corresponding author: S. Naik, sachi@ucc.ie

Received: 27 May 2003
Accepted: 21 January 2004

Abstract

We present here results obtained from three BeppoSAX observations of the accretion-powered X-ray pulsar SMC X-1 carried out during the declining phases of its 40-60 days long super-orbital period. Timing analysis of the data clearly shows a continuing spin-up of the neutron star. Energy-resolved timing analysis shows that the pulse-profile of SMC X-1 is single peaked at energies less than 1.0 keV whereas an additional peak, the amplitude of which increases with energy within the MECS range, is present at higher energies. Broad-band pulse-phase-averaged spectroscopy of the BeppoSAX data, which is done for the first time since its discovery, shows that the energy spectrum in the 0.1-80 keV energy band has three components, a soft excess that can be modeled as a thermal black-body, a hard power-law component with a high-energy exponential cutoff and a narrow and weak iron emission line at 6.4 keV. Pulse-phase resolved spectroscopy indicates a pulsating nature of the soft spectral component, as seen in a few other binary X-ray pulsars, with a certain phase offset with respect to the hard power-law component. Dissimilar shape and phase of the soft and hard X-ray pulse profiles suggest a different origin of the soft and hard components.