The young binary DQ Tau: A hunt for X-ray emission from colliding magnetospheres

The young high-eccentricity binary DQ Tau exhibits powerful recurring millimeter-band (mm) flaring attributed to collisions between the two stellar magnetospheres near periastron, when the stars are separated by only 8 R ₁. These magnetospheric interactions are expected to have scales and magnetic field strengths comparable to those of large X-ray flares from single pre-main-sequence stars observed in the Chandra Orion Ultradeep Project (COUP). To search for X-rays arising from processes associated with colliding magnetospheres, we performed simultaneous X-ray and mm observations of DQ Tau near periastron phase. We report here several results. (1) As anticipated, DQ Tau was caught in a flare state in both mm and X-rays. A single long X-ray flare spanned the entire 16.5 hr Chandra exposure. (2) The inferred morphology, duration, and plasma temperature of the X-ray flare are typical of those of large flares from COUP stars. (3) However, our study provides three lines of evidence that this X-ray flare likely arises from colliding magnetospheres: the chance of capturing a large COUP-like flare within the span of our observation is small, the relative timing of the X-ray and mm flares indicates the Neupert effect and is consistent with a common coronal structure, the size of the emitting coronal structure (4-5 R ₁) inferred from our analysis (which is admittedly model dependent and should be considered with caution) is comparable to half the binary separation. (4) The peak flare X-ray luminosity is in agreement with an estimate of the power dissipated by magnetic reconnection within the framework of a simple model of interacting magnetospheres.