Program: GN-2016A-DD-5

Accretion outbursts in young stellar objects (YSOs) are rare and not yet fully understood. While bursts of low-/intermediate-mass objects were found and studied, so far none was found in high-mass YSOs (HMYSOs) associated with masers. This situation changed recently with our detection of the burst of S255IR NIRS3, a ~20M_sun HMYSO. Our follow-up NIR imaging yielded evidence for a light echo emerging from the cavities of the bipolar outflow. The much lower optical depth of these lobes compared to the direct line-of-sight toward the HMSYO offers the chance to detect spectral features of the burst in scattered light. While our recent SINFONI spectroscopy showed an almost featureless red spectrum on the source only, it revealed a wealth of lines and a stronger continuum in scattered light indeed. These features are not present in pre-outburst archival data. Since the object is no longer visible from the southern hemisphere, 2nd epoch spectroscopy shall be obtained with NIFS before the end of its visibility period to follow the spectral evolution of the burst. Time-resolved spectroscopy of this extraordinary event bears the potential to disclose the origin of the burst.