Delayed Soft X-Ray Emission Lines in the Afterglow of GRB 030227

Abstract

Strong delayed X-ray line emission is detected in the afterglow of gamma-ray burst GRB 030227, appearing near the end of the XMM-Newton observation, nearly 20 hr after the burst. The observed flux in the lines, not simply the equivalent width, sharply increases from an undetectable level (<1.7×10^-14 ergs cm^-2 s^-1, 3 σ) to 4.1^+0.9_-1.0×10^-14 ergs cm^-2 s^-1 in the final 9.7 ks. The line emission alone has nearly twice as many detected photons as any previous detection of X-ray lines. The lines correspond well to hydrogen- and/or helium-like emission from Mg, Si, S, Ar, and Ca at a redshift z=1.39^+0.03_-0.06. There is no evidence for Fe, Co, or Ni-the ultimate iron abundance must be less than a tenth that of the lighter metals. If the supernova and GRB events are nearly simultaneous, there must be continuing sporadic power output after the GRB of a luminosity >~5×10⁴⁶ ergs s^-1, exceeding all but the most powerful quasars.