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 Hα image obtained with the ACS imager on board HST, and taking into account the known proper motions of HH 210 emission 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 optical/infrared counterpart. Spectral fitting indicates for both sources a plasma temperature of ~0.8 MK and absorption-corrected X-ray luminosities of about 10³⁰ 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 ~12 000 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.