9 October 2003
9 October 2003
Speaker: Don Lamb (Univ. of Chicago)
Scientific highlights of the HETE-2 mission
The HETE-2 mission has been highly productive. It has observed more
than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per
year, and has localized 43 GRBs to date. Twenty-one of these
localizations have led to the detection of X-ray, optical, or radio
afterglows, and as of now, 11 of the bursts with afterglows have
redshift determinations. HETE-2 has also observed more than 45 bursts
from soft gamma-ray repeaters, and more than 700 X-ray bursts.
HETE-2 has confirmed the connection between GRBs and Type Ic
supernovae, a singular achievement and certainly one of the scientific
highlights of the mission so far. It has established that the
isotropic-equivalent energies and luminosities of GRBs are strongly
correlated with redshift, implying that GRBs and their progenitors
evolve strongly with redshift. Both of these results have profound
implications for the nature of GRB progenitors and for the use of GRBs
as a probe of cosmology and the early universe.
HETE-2 has placed severe constraints on any X-ray or optical afterglow
of a short GRB. It has made it possible to explore the previously
unknown behavior optical afterglows at very early times, and has opened
up the era of high-resolution spectroscopy of GRB optical afterglows.
HETE-2 is also solving the mystery of ``optically dark'' GRBs, and
revealing the nature of X-ray flashes (XRFs). It has shown that XRFs
may provide unique insights into the structure of GRB jets, the rate of
GRBs, and the nature of Type Ic supernovae. Acceptance of the profound
implications of the HETE-2 results requires incontrovertible evidence
that can only come from further studies of XRFs. HETE-2 is ideally
suited to accurately and rapidly localize XRFs, and study their
spectra, whereas Swift is not. This constitutes a compelling reason
for continuing HETE-2 during the Swift mission.