We report the detection of an excess in dust continuum emission at 233 GHz ( 1.3 mm in wavelength ) in the protoplanetary disk around TW Hya revealed through high-sensitivity observations at \sim 3 au resolution with the Atacama Large Millimeter/submillimeter Array ( ALMA ) .
The sensitivity of the 233 GHz image has been improved by a factor of 3 with regard to that of our previous cycle 3 observations .
The overall structure is mostly axisymmetric , and there are apparent gaps at 25 and 41 au as previously reported .
The most remarkable new finding is a few au-scale excess emission in the south-west part of the protoplanetary disk .
The excess emission is located at 52 au from the disk center and is 1.5 times brighter than the surrounding protoplanetary disk at a significance of 12 \sigma .
We performed a visibility fitting to the extracted emission after subtracting the axisymmetric protoplanetary disk emission and found that the inferred size and the total flux density of the excess emission are 4.4 \times 1.0 au and 250 \mu Jy , respectively .
The dust mass of the excess emission corresponds to 0.03 M _ { \oplus } if a dust temperature of 18 K is assumed .
Since the excess emission can also be marginally identified in the Band 7 image at almost the same position , the feature is unlikely to be a background source .
The excess emission can be explained by a dust clump accumulated in a small elongated vortex or a massive circumplanetary disk around a Neptune mass forming-planet .