Study of Gamma-Ray Bursts and Afterglows using HETE-2 Satellite

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The HETE-2 satellite is a small astronomical satellite for mainly studying gamma-ray bursts (GRBs). It was launched on 9^<th> of October in 2000. After having tested functioning of the instruments and adjusted the on-board software during May through August, HETE-2 began steady observations in midsummer of 2001. The satellite operation, maintaining the scientific instruments and quick-look analyses are conducted by the HETE-2 operation team at Mission Operation Center in MIT together with the Japanese team, staffs and graduate students in RIKEN, AGU, Tokyo Tech and NAO. The three scientific instruments are normally working except for one out of four counters in the X-ray detector, of which function was lost by an accident perhaps due to an encounter with a small space debris.HETE-2 successfully localizes GRB locations and sends prompt notifications to ground observers with delay of a few tens of seconds which is three orders of magnitude faster than that of previous experiments such as BeppoSAX. Thereby early afterglows have been observable and it is found that some show very quick decay in time and others display complex structure in their early light curves.Remarkable observational result recently made is that the discovery of a spectral component of Type Ic Supernova in optical spectra of GRB030329 afterglow. This results in compelling evidence of association between GRBs and SNs.The scientific instruments carried by HETE-2 are all sensitive to X-ray below 10 keV, and hereby many X-ray Rich GRBs and X-ray Flashes are detected. The observational data accumulated by HETE-2 suggest that these phenomena have similar properties and thereby a same astrophysical origin.HETE-2 also discovered an unknown zone of high density charged particles around the equator above Ecuador which displayed time variability correlated with the solar activity.