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The galactic black hole candidate Cygnus X-1, one of the brightest sources inthe sky, is the first ever black hole candidate to be discovered. Despite beinga very well-studied object due to its persistent brightness in X-rays, therehas been much difficulty in determining its mass since its discovery. In spiteof continuous efforts since the early nineteen seventies, there is yet noconcensus on its mass for nearly four decades. The uncertainties in the massmeasurements are due to the high degree of error involved in the measurement ofits distance. In 2011, Orosz et al. constrained the mass of this object to be M= 14.8 +/- 1.0 M_Sun using dynamical methods. In this paper, we obtained themass of Cygnus X-1, using a completely independent method, namely, carrying outthe spectral analysis using Two Component Advective Flow (TCAF) solution basedfits file and the archival data of RXTE PCA instrument. Our result does notrequire the distance of the source or the information about the companion. Eachspectral fit with the TCAF gives one best fitted mass. Averaging fitted massesof Cygnus X-1 over a span of five months of observation during its persistenthard phase, mass of the source comes out to be M_avg = 14.20 +/- 0.36 M_Sun,which is consistent with the dynamically estimated mass.

Constraining Mass of Cygnus X-1 from Analysis of the Hard State Spectral Data using TCAF Solution