The discovery of a new non-thermal X-ray filament near the Galactic Centre

Abstract

We report the discovery by XMM-Newton and Chandra of a hard extended X-ray source (XMM J174540-2904.5) associated with a compact non-thermal radio filament (the Sgr A-E `wisp'= 1LC 359.888-0.086 = G359.88-0.07), which is located within ~4 arcmin of the Galactic Centre. The source position is also coincident with the peak of the molecular cloud M-0.13-0.08 (the `20 km s^-1' cloud). The X-ray spectrum is non-thermal with an energy index of 1.0^+1.1_-0.9 and a column density of 38^+7_-11× 10²² H cm^-2. The observed 2-10 keV flux of 4 × 10^-13 erg s^-1 cm^-2 converts to an unabsorbed X-ray luminosity of 1 × 10³⁴ erg s^-1 assuming a distance of 8.0 kpc. The high column density strongly suggests that this source is located in or behind the Galactic Centre region. Taking account of the broad-band spectrum, as well as the source morphology and the positional coincidence with a molecular cloud, we conclude that both the radio and X-ray emission are the result of synchrotron radiation. This is the first time that a filamentary structure in the Galactic Centre region has been shown, unequivocally, to have a non-thermal X-ray spectrum.