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 forthcomingSVOMera in two aspects. First, our simulation indicates that the color acquired from theSVOM/VT blue and red channels is effective in discriminating between low-z(z less than or similar to 3) and distant GRB candidates until z similar to 6. Second, 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-iso/E-peak(2) relationship) is roughly confirmed, although the confirmation is dissatisfactory at the large L-iso/E-peak(2) end. We believe that this issue can be further addressed in the SVOM era by a larger spectroscopy sample, thanks to its capability of rapid identification of optical candidates of afterglow and its anti-solar pointing strategy.