X-Ray Observation of the Lynds 1157 Dark Cloud Region with ASCA

Abstract

An ASCA observation of a region containing a Class 0 protostar IRAS 20386+6751 in the Lynds 1157 dark cloud, has been carried out. The protostar was not detected, and the 95% upper limit to the luminosity depends on the assumed NH: LX(0.5–10 keV) < 1.1 × 1031 erg s−1 for NH = 1 × 1023 cm−2. A Class I protostar in Lynds 1152, IRAS 20353+6742, in the same field was also undetected with an upper limit about three-times as much as the Lynds 1157 level. Besides these non detections, nine new X-ray sources were detected and a spectral analysis was performed for 4 sources. One object (AX J2038+6801) shows a hard spectrum with a temperature of kT ∼ 8 keV or a power-law photon index of ∼ 2.0 and absorbed with NH ∼ 2 × 1022 cm−2. Another fainter one (AX J2036 + 6800) has a soft spectrum with most of the emission falling below 2 keV. We examine the possible nature of these new X-ray sources based on their spectral properties.