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We have recently published observations of significant flux densityvariations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main andNorth (De Pree et al. 2014). To further study these variations, we have madenew 7 mm continuum and recombination line observations of Sgr B2 at the highestpossible angular resolution of the Karl G. Jansky Very Large Array (VLA). Wehave observed Sgr B2 Main and North at 42.9 GHz and at 45.4 GHz in the BnAconfiguration (Main) and the A configuration (North). We compare these new datato archival VLA 7 mm continuum data of Sgr B2 Main observed in 2003 and Sgr B2North observed in 2001. We find that one of the 41 known ultracompact andhypercompact HII regions in Sgr B2 (K2-North) has decreased $\sim$27% in fluxdensity from 142$\pm$14 mJy to 103$\pm$10 mJy (2.3$\sigma$) between 2001 and2012. A second source, F3c-Main has increased $\sim$30% in flux density from82$\pm$8 mJy to 107 $\pm$11 mJy (1.8$\sigma$) between 2003 and 2012. F3c-Mainwas previously observed to increase in flux density at 1.3 cm over a longertime period between 1989 and 2012 (De Pree et al. 2014). An observation ofdecreasing flux density, such as that observed in K2-North, is particularlysignificant since such a change is not predicted by the classical hypothesis ofsteady expansion of HII regions during massive star accretion. Our newobservations at 7 mm, along with others in the literature, suggest that theformation of massive stars occurs through time-variable and violent accretion.

Evidence of Short Timescale Flux Density Variations of UC HII regions in Sgr B2 Main and North