We report results of an in-depth study of the long-term soft \gamma -ray ( 30 keV – 1.7 MeV ) flux and spectral variability of the transient source GRO J 1719 - 24 that was first discovered by BATSE and SIGMA in the fall of 1993 .
Our results were obtained from the JPL BATSE-EBOP database covering a 1000-day period between 13 January 1993 and 10 October 1995 .
During this period , the source underwent a major outburst in the fall of 1993 when the 35-100 keV flux rose from a quiescent state of less than 16 mCrab before 17 September 1993 to a level of 1.5 Crab on 3 October .
The source remained in this high-intensity state over the next \sim 70 days during which the 35 - 100 keV flux decreased monotonically by \sim 33 \% to \sim 1 Crab level on 12 December , then decreased sharply to the pre-transition quiescent level of \sim 44 mCrab on 21 December where it remained until 5 September 1994 .
During a 400-day period between 5 September 1994 and 10 October 1995 , the source again underwent a series of five transitions when the 35-100 keV flux increased to low-intensity levels of \sim 200-400 mCrab , a factor of 4 - 7 times lower than that observed in 1993 .
The low and high-intensity states were characterized by two different spectral shapes .
The low-state spectra were described by a power law with spectral index of \sim 2 .
The high-state spectra on the other hand have two components : a thermal Comptonized shape below \sim 200 keV with electron temperature kT _ { e } of \sim 37 keV and optical depth \tau \sim 2.8 , and a soft power-law tail with photon index of \sim 3.4 above 200 keV that extends to \sim 500 keV .
The softer high-intensity spectrum and the harder low-intensity spectrum intercept at \sim 400 keV .
The non-thermal power-law gamma-ray component in both the high and low-intensity spectra suggests that the persistent non-thermal emission source is coupled to the hot and variable thermal emission source in the system .
Furthermore , the correlation of the spectral characteristics with the high and low-intensity state resembles that seen in two other gamma-ray emitting black-hole candidates GRO J0422+32 and Cygnus X-1 , suggesting that perhaps similar system configurations and processes are occurring in these systems .
Possible scenarios for interpreting these behaviors are discussed .