X-rays from HH 210 in the Orion nebula

Abstract

We report the detection during the Chandra Orion Ultradeep Project(COUP) of two soft, constant, and faint X-ray sources associated with the Herbig-Haro object HH 210. HH 210 is located at the tip of the NNE finger of the emission line system bursting out of the BN-KL complex, northwest of the Trapezium cluster in the OMC-1 molecular cloud. Using a recent Himage obtained with the ACS imager on board HST, and taking into account the known proper motions of HH 210 emis- sion knots, we show that the position of the brightest X-ray source, COUP 703, coincides with the emission knot 154-040a of HH 210, which is the emission knot of HH 210 having the highest tangential velocity (425 km s −1 ). The second X-ray source, COUP 704, is located on the complicated emission tail of HH 210 close to an emission line filament and has no obvious opti- cal/infrared counterpart. Spectral fitting indicates for both s ources a plasma temperature of∼0.8 MK and absorption-corrected X-ray luminosities of about 10 30 erg s −1 (0.5-2.0 keV). These X-ray sources are well explained by a model invoking a fast- moving, radiative bow shock in a neutral medium with a density of∼12000 cm −3 . The X-ray detection of COUP 704 therefore reveals, in the complicated HH 210 region, an energetic shock not yet identified at other wavelengths.