Search for X-ray emission from young stellar objects using ASCA

To investigate X-ray emission from protostars and T Tauri stars, we observed two star forming regions, L1630 in Orion and IC348 in Perceus with the X-ray observatory ASCA. From the observation of L1630, we detected X-ray emission from the region where two Class I protostars SSV63E and SSV63W are located (hereafter SSV63E+W). The spectrum of SSV63E+W is well explained by an optically thin thermal plasma model with a high temperature of kT = 5.0 (3.3-7.9) keV and a heavy at sorption of N-H = 1.5 (1.2-1.8) x 10(23) cm(-2), suggesting that it is enbedded deep in the: surrounding dusts. A significantly large X-ray flare was detected from SSV63E+W during the present ASCA observation with the heal: flux of about 9 times that of the quiescent flux. The 0.5-10 keV luminosity of SSV63E+W was about 1 x 10(32) erg s(-1) in the quiescent state. We detected 20 X-ray sources from IC348, 17 of which were identified with the ROSAT X-ray sources. We detected two X-ray flares from the center region of IC348. One of the flare exhibited an intersting feature that the hard X-ray flare in 2.0-7.0 keV band rose faster than the soft X-ray flare in 0.7-2.0 keV band. Combining the Hare light curves with the spectral evolution of the flare, we concluded that the temperature reached to the peak earlier than the emission measure along the progress of the flare. This time lag between the temperature peal: and the peak of emission measure was observed for the first time from T Tauri stars, while such time lags are often observed in solar flares.