Detection of hard X-rays from a Class I protostar in the HH24-26 region in the Orion Molecular Cloud

We observed the HH24-26 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 SSV61 and from the region where the Class I protostars SSV63E and SSV63W are located (hereafter SSV63E+W). The spectra of both SSV63E+W and SSV61 are well explained by an optically thin thermal plasma model. The spectrum of the T Tauri star SSV61 has a low temperature of kT = 0.9 (0.7−1.2) keV and a moderate absorption of NH = 1.3 (0.9−1.7) ×1022 cm−2, while that of the protostar SSV63E+W has a high temperature of kT = 5.0 (3.3−7.9) keV and a heavy absorption of NH = 1.5 (1.2−1.8) ×1023 cm−2. The X-ray light curve of SSV63E+W showed a flare during the observation. The peak flux reached about 9 times that 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 SSV63E+W was about 1 × 10 erg s−1 in the quiescent state. The present detection of hard X-rays from SSV63E+W is remarkable, because this is the first X-ray detection of a protostar in Orion. Subject headings: stars: flare—stars: formation—stars: individual (SSV61, SSV63E+W)—stars: pre-main sequence—X-rays: stars