Nature Astronomy, 4, 506-510 (2020/May-0)
A heatwave of accretion energy traced by masers in the G358-MM1 high-mass protostar.
BURNS R.A., SUGIYAMA K., HIROTA T., KIM K.-T., SOBOLEV A.M., STECKLUM B., MacLEOD G.C., YONEKURA Y., OLECH M., OROSZ G., ELLINGSEN S.P., HYLAND L., CARATTI O GARATTI A., BROGAN C., HUNTER T.R., PHILLIPS C., VAN DEN HEEVER S.P., EISLOFFEL J., LINZ H., SURCIS G., CHIBUEZE J.O., BAAN W. and KRAMER B.
Abstract (from CDS):
High-mass stars are thought to accumulate much of their mass via short, infrequent bursts of disk-aided accretion1,2. Such accretion events are rare and difficult to observe directly but are known to drive enhanced maser emission3-6. In this Letter we report high-resolution, multi-epoch methanol maser observations toward G358.93-0.03, which reveal an interesting phenomenon: the subluminal propagation of a thermal radiation `heatwave' emanating from an accreting high-mass protostar. The extreme transformation of the maser emission implies a sudden intensification of thermal infrared radiation from within the inner (40-mas, 270-au) region. Subsequently, methanol masers trace the radial passage of thermal radiation through the environment at >=4% of the speed of light. Such a high translocation rate contrasts with the <=10 km s-1 physical gas motions of methanol masers typically observed using very-long-baseline interferometry (VLBI). The observed scenario can readily be attributed to an accretion event in the high-mass protostar G358.93-0.03-MM1. While being the third case in its class, G358.93-0.03-MM1 exhibits unique attributes hinting at a possible `zoo' of accretion burst types. These results promote the advantages of maser observations in understanding high-mass-star formation, both through single-dish maser monitoring campaigns and via their international cooperation as VLBI arrays.
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