Importance to Observe GRBs in Soft X-Ray Energies - Summary of the HAKUCHO, GINGA and ASCA Observations in Soft X-Ray Energies

Two major results of the GINGA Gamma-Ray Burst detector are (1) the detections of cyclotron lines and (2) the detections of the long lasting soft X-ray emissions. In some case, this emission preceded to the main part of emissions which were much harder than the long lasting emissions. In my first part, I will focus on the importance of measuring the long lasting X-ray emissions around 1 keV based on the possible Inverse Compton mechanism to produce gamma-ray photons. In the second part, I will summarize the ASCA activities on X-ray counterpart searches. The most case of searches showed a possible X-ray counterpart in the narrow error boxes. Although they look extragalactic objects, this is not conclusive. I will discuss these cases based on the chance probability distribution.