Radio Continuum and Water Maser Monitoring of the Outburst in HOPS 373: Free–Free Emission Does Not Respond to the Outburst

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Abstract We present Very Large Array (VLA) C -band (5 cm) continuum, K -band (1.3 cm) continuum, and water maser (22.235 GHz) monitoring of the protostar HOPS 373. We additionally present the contemporaneous monitoring for 95 sources within the 5 cm field of view for over 2 yr during the peak of the HOPS 373 outburst and an additional epoch in 2026. HOPS 373 is a binary Class 0 protostar located in the Orion star-forming region, which has been found to have an ∼4× luminosity burst from the James Clerk Maxwell Telescope Transient Survey and NEOWISE monitoring. We do not find evidence for a change in the free–free emission traced by VLA 5 cm continuum during the peak of its outburst or during the decline. Moreover, the 1.3 cm continuum does not show significant variability between the northeast and southwest components of the HOPS 373 binary. The water maser emission is highly variable toward HOPS 373; multiple velocity components are detected at different (or the same) times, and the maser spots are located close to the 1.3 cm continuum source of HOPS 373SW. There is tentative evidence for the water maser spots to be propagating away from the source, but there is not a robust connection between the outburst and the observed maser activity. The lack of correlation between the outburst and free–free emission from HOPS 373 indicates that the free–free emission may not directly respond to increases in the accretion rate and subsequently the outflow rate. The lack of a link could be due to the outflow mostly being neutral, or there may be offsets in the timescale for the free–free response.

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