Context :

Aims : The black hole binary SWIFT J1753.5–0127 is providing a unique data set to study accretion flows .
Various investigations of this system and of other black holes have not , however , led to an agreement on the accretion flow geometry or on the seed photon source for Comptonization during different stages of X-ray outbursts .
We place constraints on these accretion flow properties by studying long-term spectral variations of this source .

Methods : We performed phenomenological and self-consistent broad band spectral modeling of SWIFT J1753.5–0127 using quasi-simultaneous archived data from INTEGRAL /ISGRI , Swift /UVOT/XRT/BAT , RXTE /PCA/HEXTE , and Maxi /GSC instruments .

Results : We identify a critical flux limit , F \sim 1.5 \times 10 ^ { -8 } { erg cm ^ { -2 } s ^ { -1 } } , and show that the spectral properties of SWIFT J1753.5–0127 are markedly different above and below this value .
Above the limit , during the outburst peak , the hot medium seems to intercept roughly 50 percent of the disk emission .
Below it , in the outburst tail , the contribution of the disk photons reduces significantly and the entire spectrum from the optical to X-rays can be produced by a synchrotron-self-Compton mechanism .
The long-term variations in the hard X-ray spectra are caused by erratic changes of the electron temperatures in the hot medium .
Thermal Comptonization models indicate unreasonably low hot medium optical depths during the short incursions into the soft state after 2010 , suggesting that non-thermal electrons produce the Comptonized tail in this state .
The soft X-ray excess , likely produced by the accretion disk , shows peculiarly stable temperatures for over an order of magnitude changes in flux .

Conclusions : The long-term spectral trends of SWIFT J1753.5–0127 are likely set by variations of the truncation radius and a formation of a hot , quasi-spherical inner flow in the vicinity of the black hole .
In the late outburst stages , at fluxes below the critical limit , the source of seed photons for Comptonization is not the thermal disk , but more likely they are produced by non-thermal synchrotron emission within the hot flow near the black hole .
The stability of the soft excess temperature is , however , not consistent with this picture and further investigations are needed to understand its behavior .