2000ApJ...543L.133K

XTE J1748-288 is a new X-ray transient with a one-sided radio jet. It was observed with ASCA on 1998 September 6 and 26, 100 days after the onset of the radio X-ray outburst. The spectra were modeled with an attenuated power-law model, and the absorbed 2-6 keV flux was 4.6^+1.0_–0.8x10^–11 and 2.2^+0.8_–0.6x10^–12 ergs.s^–1.cm^–2 on 1998 September 6 and 26, respectively. The light curve shows that the steady exponential decay, with an e-folding time of 14 days, lasted over 100 days and 4 orders of magnitude from the peak of the outburst. The celestial region including the source was observed with ASCA on 1993 October 1 and 1994 September 22, years before the discovery. During those periods, the flux was ≲10^–13 ergs.s^–1.cm^–2, below the ASCA detection limit. The jet blob colliding with the environmental matter is probably not the X-ray source, although the emission mechanism is not determined. A possible detection of a K line from highly ionized iron is discussed.