K. Koyama, Y. Maeda, M. Ozaki, S. Ueno, Y. Kamata, Y. Tawara, S. Skinner, S. Yamauchi

Abstract

Advanced Satellite for Cosmology and Astrophysics (ASCA) obtained broad-band (0.8-12 keV) images and spectra of the central region of the Rho Ophiuchi dark cloud in 1993 August. The 38-ks observation detected at least eleven sources (S/N greater than or equal to 3), including the X-ray bright pre-main sequence star DoAr 21 and embedded infrared sources with no optical counterparts. Hard X-rays up to approximately equals 8 keV were detected from DoAr 21 (whose light curve shows no evidence for variability) and from a flaring source lying in a region of high visual extinction. Thermal spectral fits for the brightest source give kT approximately 2 keV and hydrogen column densities NH approximately 1022 cm-2. The spectrum of a region in the center of the field where no discrete sources were detected shows hard, heavily absorbed emission that is most likely the integrated contribution of a number of a deeply embedded young stars below the detection limit.