A Pilot Study of Catching High-$z$ GRBs and Exploring Circumburst
  Environment in the Forthcoming SVOM Era
  Rapid spectroscopy of GRB afterglows is an important and hard task. Based on
the archival XS-GRB spectral database, we here perform a pilot study on the
afterglow's spectroscopy in the forthcoming \it SVOM \rm era in two aspects. At
first, our simulation indicates that the color acquired from the \it SVOM\rm/VT
blue and red channels is effective in discriminating between low-$z$
($z\lesssim3$) and distant GRB candidates until $z\sim6$. Secondly, by doubling
the sample size, we find that the previously proposed global photoionization
response of the circumburst gas to the prompt emission (i.e., the
CIV/CII-$L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$ relationship) is roughly
confirmed, although the confirmation is dissatisfactory at the large
$L_{\mathrm{iso}}/E^2_{\mathrm{peak}}$ end. We believe that this issue can be
further addressed in the \it SVOM \rm era by larger spectroscopy sample, thanks
to its capability of rapid identification of optical candidates of afterglow
and its anti-solar pointing strategy.
