Radiative transfer modeling of outbursts of massive young stellar objects

Young stellar objects (YSOs) accrete up to half of their material in short periods of enhanced mass accretion. These episodic accretion outbursts imply afterglows, which are observable at IR wavelengths (sometimes even years after the end of the burst). They are caused by the reprocessing of the burst energy within the dense natal environments of the YSOs. Bursts can impact the surrounding cloud core on all scales, from the innermost tens of au (dust sublimation), up to a few hundreds and 1000 au (disk, the site of possible planet formation), and the more extended cloud core (reservoir of cold dust). For massive YSOs (MYSOs), accretion outbursts are of special importance, as they serve as diagnostics in highly obscured regions. Only since 2015 six MYSO bursts have been discovered. Within this work, two outbursting MYSO's within different evolutionary stages, the young source G358.93-0.03 MM1 and the more evolved one G323.46-0.08, are investigated, and the major burst parameters are derived. For both sources, follow-up observations with the airborne SOFIA observatory were performed to detect the far infrared afterglows. All together, we took three burst-/post-observations. The burst parameters are needed to understand the accretion physics and to conclude on the possible triggering mechanisms behind it. Up to today, G323's burst is the most energetic one ever observed for a MYSO (with a released energy of $\approx 10^{47}, \rm erg$). G358's burst was about two orders of magnitude weaker and shorter (2 months instead of 8 years). We suggest that G358's burst was caused by the accretion of a spiral fragment (or a small planet), where G323 accreted a heavy object (a planet or even a potential companion). To model those sources, we use radiative transfer (RT) simulations (static and time-dependent). Additionally, we develop (and benchmark) a Python routine (TFitter), which allows to fit various epochs. This is the first work to apply time-dependent RT to a real MYSO.