The Redshift of the Optical Transient Associated with GRB 010222

Abstract

The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the BeppoSAX satellite. Prompt identification of the associated optical transient (OT) allowed for spectroscopy with the Tillinghast 1.5 m telescope at F. L. Whipple Observatory while the source was still relatively bright ( mag), within 5 hr of the R 18.6 burst. The OT shows a blue continuum with many superposed absorption features corresponding to metal lines at , 1.157, and possibly also 0.928. The redshift of GRB 010222 is therefore unambiguously placed z p 1.477 at . The high number of Mg ii absorbers and especially the large equivalent widths of the Mg ii, z 1.477 Mg i, and Fe ii absorption lines in the system further argue either for a very small impact parameter z p 1.477 or that the system is the GRB host galaxy itself. The spectral index of the OT is relatively steep, z p 1.477