Identification of a high-velocity compact nebular filament 2.2 arcsec
  south of the Galactic Centre
  The central parsec of the Milky Way is a very special region of our Galaxy;
it contains the supermassive black hole associated with Sgr A* as well as a
significant number of early-type stars and a complex structure of streamers of
neutral and ionized gas, within two parsecs from the centre, representing a
unique laboratory. We report the identification of a high velocity compact
nebular filament 2.2 arcsec south of Sgr A*. The structure extends over ~1
arcsec and presents a strong velocity gradient of ~200 km s^{-1} arcsec^{-1}.
The peak of maximum emission, seen in [Fe III] and He I lines, is located at
d{\alpha} = +0.20 +/- 0.06 arcsec and d{\delta} = -2.20 +/- 0.06 arcsec with
respect to Sgr A*. This position is near the star IRS 33N. The velocity at the
emission peak is Vr = -267 km s^{-1}. The filament has a position angle of PA =
115{\degr} +/- 10{\degr}, similar to that of the Bar and of the Eastern Arm at
that position. The peak position is located 0.7 arcsec north of the binary
X-ray and radio transient CXOGX J174540.0-290031, a low-mass X-ray binary with
an orbital period of 7.9 hr. The [Fe III] line emission is strong in the
filament and its vicinity. These lines are probably produced by shock heating
but we cannot exclude some X-ray photoionization from the low-mass X-ray
binary. Although we cannot rule out the idea of a compact nebular jet, we
interpret this filament as a possible shock between the Northern and the
Eastern Arm or between the Northern Arm and the mini-spiral "Bar".
