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Project Progress

In this reporting period, we studied long-term X-ray variations of the protostar V1647 Ori that currently experiences strong mass accretion, and of many young stellar objects in the active star-forming region surrounding V1647 Ori. We also studied the relation of temporal variations in the intensities of their X-ray and optical/near-infrared (IR) emissions.

We triggered a reserved Target-of-Opportunity (ToO) observation of the erupting protostar V1647 Ori with the XMM-Newton observatory in 2013 March 9, to monitor its recent X-ray activity. The last X-ray observations of this star before the ToO observation, performed with the XMM-Newton and Swift X-ray observatories in 2010, suggested a drop in the X-ray flux by an order of magnitude. The new observation in 2013, again, showed a similarly low X-ray flux level, suggesting that the flux decrease observed in 2010 and 2013 was not caused by a short-term variation, such as rotational modulation, but was an intrinsic decay of the X-ray activity. The optical and near-IR fluxes stayed high until 2013 at the outburst peak level, and therefore the mass accretion outburst would have persisted until now. This means that a part of the mechanism that induces the X-ray activity, possibly related to the stellar magnetic field, ceased to work after ~2010. In response to this ToO observation, we triggered coordinated optical/near-IR observations of V1647 Ori using the Japanese observatory network. The optical/near-infrared fluxes did not vary significantly around the X-ray observation, while the Br gamma line (which is a good tracer of mass accretion) might have varied significantly.

In the CCD field of view of the 11 monitoring observations of V1647 Ori, the Chandra X-ray observatory detected 52 X-ray emitting young stellar objects associated with the active star-forming region Lynds 1630. The X-ray fluxes from these young stellar objects varied by orders of magnitude on yearly timescales.