Observations of Gamma-Ray Afterglows with Wide-field Optical Telescope

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We bave successfulty obtained wide field images of 5degree times 5degrees using the prototype telescope built for the TONBO projed. However, we coald not detect any optical afterglow from the Gamma-Ray Burst <GRB) due to more than one-year delay of the laanch of tbe HETE-2 satellite which we planned to utilize for GRB Iocations, and umknown instability of the telescope focus plane depending on the temperature.The techniques and knowledge obtained throagh this research, for instance a method of the rapid transfer of GRB ioformation via Internet, cad be utilized in the project of robotic telescope, RIBOTS. Furtbermore, the techniqae developed in this research on detecting unknown transients can be employed in the follow-up obselvations of GRBs at the Kiso Observatony A wide-field-of-view Air Cherenkov telescope nov under development by our group employs the knowledge obtained throagb this research. Some researchers have reported the detection of very bigh energy gamma-rays, over 100 GeV, from GRBs while they were rather statistically poor detections. It is clearty important to confirm such high energy gamma-ray emissions from GRBs. Ordinary Cherenkov tetescopes, however, have only small field-of-view and there needs a new type telescope with large field-of-view.We studied X-ray afterglows of GRBs as well. The most important result we got using the ASCA, lapanese X-ray satetlite, is to detect a emission, line like structure in the spectrum of GRB970828. We show that this structare can be interpreted as a radidative recombination edge from irons around the barst source, wbich is fully consistent with the redshift given by the optical spectroscopy of the afterglow. Tnts iadicates tbe existence of iron-rich environment of GRBS and sports the GRB scenario of massive star collapse.