The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Strong Increase in Mid-Infrared Continuum Emission

Abstract In recent years, dramatic outbursts have been identified toward massive protostars via infrared and millimeter dust continuum molecular maser emission. The longest lived outburst (>6 yr) persists in NGC 6334 I-MM1, a deeply embedded object with no near-IR counterpart. Using FORCAST HAWC+ on SOFIA, we obtained the first mid-IR images of this field since began. Despite being undetected pre-outburst ground-based 18 μ m images, MM1 is now brightest region at all three wavelengths (25, 37, 53 m), exceeding UCHII MM3 (NGC F). Combining SOFIA data ALMA imaging four wavelengths, construct spectral energy distribution combination nearby hot core MM2. best-fit Robitaille radiative transfer model yields luminosity (4.9 ± 0.8) × 10 4 L ⊙ . Accounting for an estimated ratio MM1:MM2 = 2.1 0.4, has increased by factor 16.3 4.4. implies protostar mass 6.7 M , which can produce ionizing photon rate required to power HCHII surrounding likely outbursting MM1B. total duration exceed S255IR-NIRS3 ≳3, suggesting different scale event involving expansion protostellar photosphere (to ≳20 R ), thereby supporting higher accretion (≳0.0023 yr −1 ) reducing rate. grid hydrodynamic models Meyer et al., magnitude (3) places I-MM1 moderate (∼0.1–0.3 hence long (∼40–130 yr).