GCN Circular 228
T. Murakami, M. Ishida and T. Dotani, Institute of Space and Astronautical Science, and A. Yoshida and N. Kawai, Institute of Physical and Chemical Research, report: The X-ray astronomy satellite ASCA has been observing the X-ray afterglow of GRB990123 since January 25.688 (UT). The observation started about 55 hours after the burst, but the X-ray afterglow is still bright. ASCA will continue observing the source until January 26.806 (UT). With only one forth of the dataset down-linked at the tracking station, the flux is about 1 x 10E-12 erg cmE-2 sE-1 in 2 to 10 keV assuming a power-law with the photon index of -1.6.