No abstract

We carried out the systematic spectral analysis for 11 black hole candidates (BHCs) in the low/hard state, using archival RXTE and Beppo-SAX data with the energy coverage of 2-250 keV. For in total 301 observations, the simple analytic model, i.e. power-law with an exponential cutoff modified with a smeared edge model, was adopted. Consequently, we found that the photon index is distributed over 1.2-1.8, and the high energy cutoff was more than 40 keV. We also found a clear anti-correlation between the luminosity and the high energy cutoff when the luminosity is larger than 2 ¡ 10 37 erg s¢ 1 . In addition, we performed the same analysis for one neutron star (GS 1826-238) and one active galactic nuclei (IC 4329A) for comparison. No clear differences are found among the three category sources, suggesting that the accretion mechanisms in the low/hard states are independent of mass of the central objects.