Time-evolving modelling for fits to X-ray afterglows

We perform fits to a sample of six XMM Newton GRB afterglow spectra using the newly developed Time Evolving PhotoIonisation Device (TEPID) ionised absorber model. We fit the data first with a single ionised screen and with a combined optically derived neutral+ionised screen. The hydrogen equivalent optical neutral screen was restricted to the range estimated from optical absorption features for each of the bursts. We find that our model predicts an ultra-high ionisation region in the immediate vicinity of the GRB and compared to a standard neutral absorber improves upon the best fit for five out of the six bursts in our sample. We present here our results for the GRB 061121. The analysis procedure and full set of results will be published in an upcoming paper (Thakur et al., in prep)