SIMBAD references

We present timing and spectral analysis of Rossi X-ray Timing Explorer-Proportional Counter Array observations of SMC X-1 between 1996 January and 2003 December. From observations around 1996 August 30 with a time-span of ∼6d, we obtain a precise timing solution for the source and resolve the eccentricity as 0.00089(6). We find an orbital decay rate of which is close to the previous results. Using our timing analysis and the previous studies, we construct a ∼30yr long pulse period history of the source. We show that frequency derivative shows long- (i.e. more than a few years) and short-term (i.e. order of days) fluctuations. From the spectral analysis, we found that all spectral parameters except Hydrogen column density showed no significant variation with time and X-ray flux. Hydrogen column density is found to be higher as X-ray flux gets lower. This may be due to the increase in soft absorption when the pulsar is partially obscured as in Her X-1 or may just be an artefact of the tail of a soft excess in energy spectrum.