Hot circumstellar material resolved around β Pic with VLTI/PIONIER

Aims. We aim at resolving the circumstellar environment around beta Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., similar to 4 AU). Methods. Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results. We detected near-infrared circumstellar emission around beta Pic that accounts for 1.37% +/- 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., similar to 200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (greater than or similar to 1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of beta Pic with an unprecedented accuracy (theta(LD)=0.736 +/- 0.019 mas). Conclusions. The presence of a small H-band excess originating in the vicinity of beta Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded.