Q&A: X-ray Astronomy

Q:
I want to know if the image of GRB-010222 can be examined for red shift. Can GRBs be measured that way?

A:
The best way to get a red shift for a gamma ray burst is to catch it soon after the outburst and measure the red shift of the host galaxy with an optical telescope. This is sometimes possible with an X-ray telescope (for example GRB 991216). For GRB 010222, observations using the Keck telescope indicate that the red shift is 2.04.

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 (R~=18.6 mag), within 5 hr of the burst. The OT shows a blue continuum with many superposed absorption features corresponding to metal lines at z=1.477, 1.157, and possibly also 0.928. The red shift of GRB 010222 is therefore unambiguously placed at z>=1.477. The high number of Mg II absorbers and especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption lines in the z=1.477 system further argue either for a very small impact parameter or that the z=1.477 system is the GRB host galaxy itself. The spectral index of the OT is relatively steep, Fν~ν-0.89+/-0.03, and this cannot be caused by dust with a standard Galactic extinction law in the z=1.477 absorption system.