An extraordinary outburst in the massive protostellar system NGC6334I-MM1 : quadrupling of the millimeter continuum
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Based on sub-arcsecond ALMA and SMA 1.3 mm continuum images of the massive protocluster NGC6334I obtained in 2015 and 2008, we find that the dust emission from MM1 has increased by a factor of 4.0±0.3 during the intervening years, and undergone a significant change in morphology. The continuum emission from the other cluster members (MM2, MM4 and the UCHII region MM3=NGC6334F) has remained constant. Long term single-dish maser monitoring at HartRAO finds that multiple maser species toward NGC6334I flared beginning in early 2015, a few months before our ALMA observation, and some persist in that state. New ALMA images obtained in July-August 2016 at 1.1 and 0.87 mm confirm the changes with respect to SMA 0.87 mm images from 2008, and indicate that the (sub)millimeter flaring has continued for at least a year. The excess continuum emission, centered on the hypercompact HII region MM1B, is extended and elongated (1.6'' x 1.0'' ∼ 2100 x 1300 au) with multiple peaks, suggestive of general heating of the surrounding subcomponents of MM1, some of which may trace clumps in a fragmented disk rather than separate protostars. In either case, these remarkable increases in maser and dust emission provide direct observational evidence of a sudden accretion event in the growth of a massive protostar yielding a sustained luminosity surge by a factor of 70±20, analogous to the largest events in simulations by Meyer et al. (2017). This target provides an excellent opportunity to assess the impact of such a rare event on a protocluster over many years.
Hunter , T R , Brogan , C L , MacLeod , G , Cyganowski , C J , Chandler , C J , Chibueze , J O , Friesen , R , Indebetouw , R , Thesner , C & Young , K H 2017 , ' An extraordinary outburst in the massive protostellar system NGC6334I-MM1 : quadrupling of the millimeter continuum ' Astrophysical Journal Letters .
Astrophysical Journal Letters
© 2017, American Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at iopscience.iop.org
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