GRS 1915+105: the distance, radiative processes and energy-dependent   variability
  We present an exhaustive analysis of five broad-band observations of GRS 1915+105 in two variability states, chi and omega, observed simultaneously by the PCA, HEXTE and OSSE. We find all the spectra well fitted by Comptonization of disc blackbody photons, with very strong evidence for the presence of a nonthermal electron component in the Comptonizing plasma. Both the energy and the power spectra in the chi state are typical to the very high/intermediate state of black-hole binaries. The spectrum of the omega state is characterized by a strong blackbody component Comptonized by thermal electrons and a weak nonthermal tail. We then calculate rms spectra (fractional variability as functions of energy) for the PCA data. We accurately model the rms spectra by coherent superposition of variability in the components implied by the spectral fits, namely a less variable blackbody and more variable Comptonization. The latter dominates at high energies, resulting in a flattening of the rms at high energies in most of the data. This is also the case for the spectra of the QPOs present in the chi state. Then, some of our data require a radial dependence of the rms of the disc blackbody. We also study the distance to the source, and find 11 kpc as the most likely value, contrary to a recent claim of a much lower value. 
Andrzej A. Zdziarski, Marek Gierlinski, A. R. Rao, S. V. Vadawale,   Joanna Mikolajewska