The diffuse interstellar band around 8620 {\AA} I. Methods and
  application to the GIBS data set
  We developed a set of procedures to automatically detect and measure the DIB
around 8620 {\AA} (the Gaia DIB) for a wide range of temperatures. The DIB
profile is fit with a Gaussian function. Specifically, the DIB feature is
extracted from the spectra of late-type stars by subtracting the corresponding
synthetic spectra. For early-type stars we applied a specific model based on
the Gaussian process that needs no prior knowledge of the stellar parameters.
The method was tested on $\sim$5000 spectra from the Giraffe Inner Bulge Survey
(GIBS). After validation, we obtained 4194 reasonable fitting results from the
GIBS database. An EW versus $E(J\,{-}\,K_{\rm S})$ relation is derived as
$E(J\,{-}\,K_{\rm S})\,{=}\,1.875\,({\pm}\,0.152)\,{\times}\,{\rm
EW}\,{-}\,0.011\,({\pm}\,0.048)$, according to $E(B\,{-}\,V)/{\rm
EW}\,{=}\,2.721$, which is highly consistent with previous results toward
similar sightlines. After a correction based on the VVV database for both EW
and reddening, the coefficient derived from individual GIBS fields,
$E(J\,{-}\,K_{\rm S})/{\rm EW}\,{=}\,1.884\,{\pm}\,0.225$, is also in perfect
agreement with literature values. Based on a subsample of 1015 stars toward the
Galactic center within $-3^{\circ}\,{<}\,b\,{<}\,3^{\circ}$ and
$-6^{\circ}\,{<}\,l\,{<}\,3^{\circ}$, we determined a rest-frame wavelength of
the Gaia DIB as 8620.55 {\AA}. A Gaussian profile is proved to be a proper and
stable assumption for the Gaia DIB as no intrinsic asymmetry is found.
