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.

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