The GRB 011211 X-ray lines: Toward resolving the significance debate

We demonstrate for the GRB 011211 X-ray afterglow lines that the significance estimation methods used by Reeves et al. and Rutledge & Sako are consistent and that the conflicting estimates found by those authors arise from different assumptions in the continuum modeling. If the column density is fixed at the Galactic value as in the Reeves et al. analysis, then both methods agree that the lines are significant at the ∼3 σ level, in agreement with the original claim of Reeves et al. If we allow the column density to vary, values in excess of the Galactic column density are preferred by the data, and the lines are found from both methods to be ∼1.5 σ significant, in agreement with the claim of Rutledge & Sako. We argue that the column density parameter should be fixed at the Galactic value when analyzing the portion (first 5 ks) of the XMM-Newton EPIC-PN spectrum containing the potential emission lines, because the full 25 ks observation is well modeled assuming Galactic absorption. The presence of cold gas local to the gamma-ray burst, which would be required to produce a time-variable N_H, is unlikely. We also discuss the case for emission lines for GRB 030227, for which the value of N_H is not critical.