We present for the first time a study of the 3–200 keV broad band spectra of the bursting atoll source 4U 1728-34 ( GX 354-0 ) along its hardness intensity diagram .
The analysis was done using the INTEGRAL public and Galactic Center deep exposure data ranging from February 2003 to October 2004 .
The spectra are well described by a thermal Comptonization model with an electron temperature from 35 keV to 3 keV and Thomson optical depth , \tau _ { T } , from 0.5 to 5 in a slab geometry .
The source undergoes a transition from an intermediate/hard to a soft state where the source luminosity increases from 2 to 12 % of Eddington .
We have also detected 36 type I X-ray bursts two of which show photospheric radius expansion .
The energetic bursts with photospheric radius expansion occurred at an inferred low mass accretion rate per unit area of \dot { m } \sim 1.7 \times 10 ^ { 3 } g cm ^ { -2 } s ^ { -1 } , while the others at a higher one between 2.4 \times 10 ^ { 3 } -9.4 \times 10 ^ { 3 } g cm ^ { -2 } s ^ { -1 } .
For 4U 1728-34 the bursts ’ total fluence , and the bursts ’ peak flux are anti-correlated with the mass accretion rate .
The type I X-ray bursts involve pure helium burning either during the hard state , or during the soft state of the source .