Modelling the environment around five ultracool dwarfs via the radio domain

Abstract

We present the results of a series of short radio observations of six ultracool dwarfs made using the upgraded VLA in S (2--4GHz) and C (4--7GHz) bands. LSR J1835+3259 exhibits a 100 percent right-hand circularly polarised burst which shows intense narrowband features with a fast negative frequency drift of about $-30$ MHz ${\text{s}}^{-1}$. They are superimposed on a fainter broadband emission feature with a total duration of about 20 minutes, bandwidth of about 1 GHz, centred at about 3.5 GHz, and a slow positive frequency drift of about 1 MHz ${\text{s}}^{-1}$. This makes it the first such event detected below 4 GHz and the first one exhibiting both positive and negative frequency drifts. Polarised radio emission is also seen in 2MASS J00361617+1821104 and NLTT 33370, while LP 349-25 and TVLM 513-46546 have unpolarised emission and BRI B0021-0214 was not detected. We can reproduce the main characteristics of the burst from LSR J1835+3259 using a model describing the magnetic field of the dwarf as a tilted dipole. We also analyse the origins of the quiescent radio emission and estimate the required parameters of the magnetic field and energetic electrons. Although our results are non-unique, we find a set of models which agree well with the observations.

16 pages, 9 figures, 5 tables

References in corpus (22)

• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Large-scale magnetic topologies of late M dwarfs
• Simulations of dynamo action in fully convective stars
• Post-correlation radio frequency interference classification methods
• The First Direct Measurements of Magnetic Fields on Very Low-Mass Stars
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• Radio Observations of a Large Sample of Late-M, L, and T Dwarfs: The Distribution of Magentic Field Strengths
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs
• Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
• Ultra-high-time Resolution Observations of Radio Bursts on AD Leonis
• New Neighbors: Parallaxes of 18 nearby stars selected from the LSPM-north catalog
• On the Radii of Brown Dwarfs Measured with AKARI Near-Infrared Spectroscopy
• Simultaneous Multiwavelength Observations of Magnetic Activity in Ultracool Dwarfs. IV. The Active, Young Binary NLTT 33370 AB (=2MASS J13142039+1320011)
• Wideband Dynamic Radio Spectra of Two Ultra-cool dwarfs
• Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
• Rotational Modulation of M/L Dwarfs due to Magnetic Spots
• Steady and Transient Radio Emission from Ultracool Dwarfs
• Timing Analysis of the Periodic Radio and Optical Brightness Variations of the Ultracool Dwarf, TVLM 513-46546
• Towards understanding dynamo action in M dwarfs

Cited by in corpus (6)

• A scaling relationship for non-thermal radio emission from ordered magnetospheres: from the top of the Main Sequence to planets
• Evidence for a radiation belt around a brown dwarf
• Radio emission in a nearby ultracool dwarf binary: a multi-frequency study
• Searching for stellar flares from low mass stars using ASKAP and TESS
• The Potential of Detecting Radio-flaring Ultracool Dwarfs at L band in the FAST Drift-scan Survey
• A scaling relationship for non-thermal radio emission from ordered magnetospheres - II. Investigating the efficiency of relativistic electron production in magnetospheres of BA-type stars