The close T Tauri binary system V4046 Sgr: Rotationally modulated X-ray emission from accretion shocks

TL;DR

This study reveals that the X-ray emission from the accretion shocks in the V4046 Sgr binary system exhibits rotational modulation, indicating localized high-density plasma regions associated with accretion processes.

Contribution

First time time-resolved X-ray spectra of V4046 Sgr show periodic flux variations, linking high-density plasma to accretion shocks and magnetic field geometry.

Findings

X-ray emission lines vary periodically with a 1.22-day period.

High-density plasma is localized and corotates with the stars.

Results support models of accretion shocks at magnetic footpoints.

Abstract

We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotations. We find that the emission lines produced by this high-density plasma display periodic flux variations with a measured period, 1.22+/-0.01 d, that is precisely half that of the binary star system (2.42 d). The observed rotational modulation can be explained assuming that the high-density plasma occupies small portions of the stellar surfaces, corotating with the stars, and that the high-density plasma is not azimuthally symmetrically distributed with respect to the rotational axis of each star. These results strongly support models in which high-density, X-ray-emitting CTTS plasma is material heated in accretion shocks, located at the base of accretion flows tied to the system by magnetic field lines.