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publication

ASCA observations of hard X-ray emission from the Rho Ophiuchi dark cloud

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.

 
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