DISSECTING THE GRB ENVIRONMENT WITH OPTICAL AND X-RAY OBSERVATIONS

Abstract

GRB’s environment can be studied through the imprint (i.e. absorption) it leaves on the afterglow emission. Fast optical observations allowed us to observe line variability and to derive the distance and composition of the absorbing medium. However, given the huge GRB ionizing flux, this medium starts showing up in the optical spectra only at relatively large distances (100 pc). A complementary view comes from the X-ray band, where the overall contribution of all metals bends the power law X-ray afterglow spectrum. We will review and compare optical and X-ray studies of the circumbust medium.