Y. Kamata, K. Koyama, Y. Tsuboi, S. Yamauchi
Journal: Publ. of the Astronomical Society of Japan, v.49, p.461-470.
This paper presents a comprehensive study with the Japanese X-ray astronomical satellite ASCA on X-rays from the main body of the rho Ophiuchi dark cloud. We have constructed separate X-ray images using 3 energy bands and 12 time-sliced data, and thereby detected 19 X-ray sources, doubling the previous ASCA results of 11 X-ray sources. Three of the sources are associated with class-I infrared sources, which precede the T Tauri phase. Half of the 19 sources were found to be time variable, and 5 flare-like events with an averaged energy of >3times 10(35) erg were observed. With the analogy of solar flares, we estimated the flare loop height and plasma density to be 3*E(11) cm and 3*E(11) cm(-3) , respectively. Among these sources, a flare from the class-I source EL 29 exhibited an order-of-magnitude larger absorption (N_H) than in quiescence states, which may indicate the exsistence of a dense protostellar disk.