Detection of hard X-rays from a class I protostar in the HH 24-26 region in the Orion molecular cloud

We observed the HH 24-26 region in the L1630 Orion molecular cloud complex with the X-ray observatory ASCA in the 0.5-10 keV band. X-ray emission was detected from the T Tauri star SSV 61 and from the region in which the clas s I protostars SSV 63E and SSV 63W (hereafter SSV 63E+W) are located. The s pectra of both SSV 63E+W and SSV 61 are well explained by an optically thin thermal plasma model. The spectrum of the T Tauri star SSV 61 has a low te mperature of kT = 0.9 (0.7-1.2) keV and a moderate absorption of N-H = 1.3 (0.9-1.7) x 10(22) cm(-2), while that of the protostar SSV 63E+W has a high temperature of kT = 5.0 (3.3-7.9) keV and a heavy absorption of N-H = 1.5 (1.2-1.8) x 10(23) cm(-2). The X-ray light curve of SSV 63E+W showed a flar e during the observation. The peak flux reached about 9 times the intensity of the quiescent flux. The temperature and the absorption column density d o not change conspicuously during the flare. The 0.5-10 keV luminosity of S SV 63E+W was about 1 x 10(32) ergs s(-1) in the quiescent state. The presen t detection of hard X-rays from SSV 63E+W is remarkable, since this is the first X-ray detection of a protostar in Orion.