Simultaneous Chandra and Very Large Array Observations of Young Stars and Protostars in ρ Ophiuchus Cloud Core A

Abstract

A 96-ks Chandra X-ray observation of rho Ophiuchus cloud core A detected 87 sources, of which 60 were identified with counterparts at other wavelengths. The X-ray detections include 12 of 14 known classical T Tauri stars in the field, 15 of 17 known weak-lined TTS, and 4 of 15 brown dwarf candidates. The X-ray detections are characterized by hard, heavily absorbed emission. The mean photon energy of a typical source is 3 keV, and more than half of the detections are variable. Prominent X-ray flares were detected in the unusual close binary system Oph S1, the X-ray bright WTTS DoAr 21, and the brown dwarf candidate GY 31. Time-resolved spectroscopic analysis of the DoAr~21 flare clearly reveals a sequence of secondary flares during the decay phase which may have reheated the plasma. We find that the X-ray luminosity distributions and spectral hardnesses of CTTS and WTTS are similar. We also conclude that the X-ray emission of detected brown-dwarf candidates is less luminous than T Tauri stars, but spectroscopically similar. Simultaneous multifrequency VLA observations detected 31 radio sources at 6 cm, of which ten were also detected by Chandra. We report new radio detections of the optically invisible IR source WLY 2-11 and the faint H-alpha emission line star Elias 24. We confirm circular polarization in Oph S1 and report a new detection of circular polarization in DoAr 21. We find no evidence that X-ray and radio luminosities are correlated in the small sample of TTS detected simultaneously with Chandra and the VLA. We describe a new non-parametric method for estimating X-ray spectral properties from unbinned photon event.