Synchrotron emission from the T Tauri binary system V773 Tauri A

Abstract

The pre-main sequence binary system V773 Tau A shows remarkable flaring activity around periastron passage. Here, we present the observation of such a flare at a wavelength of 3 mm (90 GHz) performed with the Plateau de Bure Interferometer . We examine different possible causes for the energy losses responsible for the e-folding time of 2.31 ± 0.19 h of that flare. We exclude synchrotron, collisional, and inverse Compton losses because they are not consistent with observational constraints, and we propose that the fading of the emission is due to the leakage of electrons themselves at each reflection between the two mirror points of the magnetic structure partially trapping them. The magnetic structure compatible with both our leakage model and previous observations is that of a helmet streamer that, as in the solar case, can occur at the top of the X-ray-emitting, stellar-sized coronal loops of one of the stars. The streamer may extend up to ∼20 R * and interact with the corona of the other star at periastron passage, causing recurring flares. The inferred magnetic field strength at the two mirror points of the helmet streamer is in the range 0.12−125 G, and the corresponding Lorentz factor, γ, of the partially trapped electrons is in the range 20 < γ < 632. We therefore rule out that the emission could be of gyro-synchrotron nature: the derived high Lorentz factor proves that the nature of the emission at 90 GHz from this pre-main binary system is synchrotron radiation.

Recurring millimeter flares as evidence for star-star magnetic reconnection events in the DQ Tauri PMS binary system

“…In this subsection, we follow closely an analysis similar to that presented in Massi et al (2006) for synchrotron emission from the interacting coronae of V773 Tau A. We model the outer (large-scale) structure of the DQ Tau magnetospheres to be wellordered dipoles and we take the magnetic axes to be aligned parallel to the rotational axes, assumptions that are consistent with recent 3D extrapolations of the coronal field topology for several young stars (Gregory et al 2008).…”

“…There the authors predict that, as the outflows in a binary system combine at large stellar distances, reconnection events should result near the intersection point. Finally, the trigger might simply be a inter-coronal interaction very similar to the Massi et al (2006Massi et al ( , 2008 scenario for V773 Tau A. There the extended magnetic structure was imaged at a stellar height of 48 R .…”

“…Next we constrain the maximum density of the electrons spiraling along the field lines by calculating what the thermal Coloumb collisional losses (in hours) would need to be in order to shorten the observed decay time. We use (Petrosian 1985; Massi et al 2006):…”

The Gould’s Belt Distances Survey (Gobelins). I. Trigonometric Parallax Distances and Depth of the Ophiuchus Complex

“…Such continuum non-thermal emission has been detected around a number of low-mass young stars (e.g., Forbrich et al 2011, and references therein), and has been interpreted as coronal emission from active stellar magnetospheres. The most common mechanism appears to be gyro-synchrotron, although maser-amplified cyclotron emission (Smith et al 2003) as well as synchrotron emission (Massi et al 2006) have also been reported in rare instances. The magnetic field in which the electrons are gyrating is generated through the dynamo mechanism, which requires convection in the outer layers of the stellar interior (e.g., Dormy et al 2013).…”

Accretion Disks around low-mass Stars unveiled by the new Generation of cm to submm Arrays

“…More information can be found at http://www.skatelescope.org/ In the course of understanding how stars and planets form, there are several domains which will benefit from the high sensitivity, high angular resolution images provided by these new interferometers. In this context, here is a non exhaustive list where these new instruments would provide invaluable information: (a) Nowadays, star-disk interactions linked to stellar magnetic loops (Massi et al (2006)) are mostly observed in close (spectroscopic) binary systems which present variable emissions from a few cm up to the mm range Salter et al (2008). Thanks to their sensitivity and angular resolution, e-VLA and SKA would likely change our views in this domain by better constraining the magnetic activity of PMS TTauri stars.…”