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 class I protostars SSV 63E and SSV 63W (hereafter SSV 63E+W) are located. The spectra 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 temperature of kT = 0.9 (0.7-1.2) keV and a moderate absorption of N_H = 1.3 (0.9-1.7) × 10²² 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) × 10²³ cm^-2. The X-ray light curve of SSV 63E+W showed a flare during the observation. The peak flux reached about 9 times the intensity of the quiescent flux. The temperature and the absorption column density do not change conspicuously during the flare. The 0.5-10 keV luminosity of SSV 63E+W was about 1 × 10³² ergs s^-1 in the quiescent state. The present detection of hard X-rays from SSV 63E+W is remarkable, since this is the first X-ray detection of a protostar in Orion.