THE YOUNG BINARY DQ Tau: A HUNT FOR X-RAY EMISSION FROM COLLIDING MAGNETOSPHERES

Abstract

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 ~8Rstar. 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 (PMS) 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 hour 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 (4-5Rstar) 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.