Resolving the source of the massive protostellar accretion outburst in NGC6334I-MM1B

Though evidence for episodic accretion is now commonplace toward low mass protostars, the recent extraordinary outburst in the massive protostellar cluster NGC6334I (Hunter et al. 2017) marks only the second large episodic accretion event observed toward a deeply embedded massive protostar and casts new light on the tumultuous lives of these young objects. The unexpectedly large factor of increase in millimeter continuum emission was accompanied by an unprecedented simultaneous flaring of 10 maser transitions detected by the long-term bi-weekly maser monitoring program at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) (MacLeod et al. 2018). The dust emission and water and methanol masers have now remained in the outburst state for over four years. The combination of VLA and ALMA imaging (Brogan et al. 2018) pinpointed the origin of the outburst to a hypercompact HII region MM1B that is driving a compact well-collimated outflow traced by water masers, their proper motions, and a number of thermal molecular tracers of warm dense gas. The pre-outburst strength of the HCHII region and its bolometric luminosity are consistent with a deeply-embedded central protostar of early B- type, but it has dimmed dramatically in its free-free emission at centimeter wavelengths despite the large increase in luminosity. This combination of observations suggest a reduction in uv photons due to the rapid accretion of sufficient mass to cause the protostellar photosphere to expand and radiate at a much larger luminosity, but with a lower effective temperature. To explore this exciting possibility, we will present new ALMA images with the finest-ever resolution toward this object (<50 au) acquired during Cycle 6, along with the results from two new epochs of VLA monitoring of the continuum and maser emission.