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D. Q. Lamb (University of Chicago), HETE-2 Science Team
HETE-2 is currently localizing GRBs at a rate of ~20 yr-1, many in near real-time. As of early March 2003, HETE-2 had localized 33 GRBs; nine localizations had led to the detection of an X-ray, optical, or radio afterglow; seven GRBs had established redshifts. The HETE-2 observations of these GRBs, and the optical and radio follow-up observations of them, are solving the mystery of ``optically dark'' GRBs. They show that some GRBs are ``optically dark'' because their optical afterglow is extinguished by dust in the star-forming region in which they occur. Others are actually ``optically dim'' rather than ``optically dark'' (i.e., their optical afterglows are very much fainter than those that had been detected previously). However, even these bursts can have very bright optical afterglows at times < 10 minutes after the burst. Still other bursts are likely ``optically dark'' because they occur at very high redshift (z > 5). These bursts can be used as a powerful probe of cosmology. About 40% of the GRBs that HETE-2 has detected and localized are ``X-ray-rich.'' There may be a tendency for such ``X-ray-rich'' GRBs to have ``optically dim'' afterglows. The results of the HETE-2 mission so far highlight the importance of providing accurate, real-time localizations for GRBs, and imply that Swift will make major contributions to our understanding of GRBs.
This work was supported in part by NASA Contract NASW-4690.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.