Radio detections of southern ultracool dwarfs

Lynch, C.; Murphy, Tara; Ravi, Vikram; Hobbs, G.; Lo, Kitty; Ward, Charlotte

doi:10.1093/mnras/stw050

Cited by 35 publications

(43 citation statements)

References 62 publications

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“…As can be seen in Figure 2, different parameter sets can indeed provide equally good fits to the observed data (see the red and blue curves overplotted on the observed spectra). Similar results were obtained earlier by other authors in application to a number of ultracool dwarfs Ravi et al 2011;Lynch, Mutel & Güdel 2015;Lynch et al 2016). We note that the mentioned degeneracy between different model parameters is not removed even if the polarisation measurements are available (like in the case of 2M 0036), in contrast to the suggestions of Lynch, Mutel & Güdel (2015).…”

Section: Markov Chain Monte Carlo Analysissupporting

confidence: 90%

“…The uniform magnetic field is characterized by its strength B and viewing angle θ (relative to the line-of-sight). The energetic electrons are assumed to have an isotropic power-law spectrum with the spectral index δ in the energy range from E min = 10 keV to E max = 100 MeV; the chosen energy range is consistent with earlier simulations Ravi et al 2011;Lynch et al 2016) and agrees also with the estimations for the electrons in the Jovian radiation belts (Santos-Costa & Bolton 2008, see details below). Thus, the emission spectrum (Stokes I and V) depends on five parameters: source size L, magnetic field strength B and viewing angle θ, the total concentration of energetic electrons n b and their spectral index δ.…”

Section: Source Modelsupporting

confidence: 64%

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Modelling the environment around five ultracool dwarfs via the radio domain

Metodieva

Kuznetsov

Antonova

et al. 2016

Mon. Not. R. Astron. Soc.

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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 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 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.

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Section: Markov Chain Monte Carlo Analysissupporting

confidence: 90%

Section: Source Modelsupporting

confidence: 64%

Modelling the environment around five ultracool dwarfs via the radio domain

Metodieva

Kuznetsov

Antonova

et al. 2016

Mon. Not. R. Astron. Soc.

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“…However, our detection efficiency of ∼5% for our not-previously detected targets does not represent an improvement over previous surveys, as summarized by Route & Wolszczan (2013) and Lynch et al (2016). Both publications reveal that the detection rate of unbiased radio surveys for UCDs remains stubbornly low, at ∼7-10%, independent of instrumentation and survey volume.…”

Section: Ucd Radio Flaring Observing Statisticssupporting

confidence: 47%

THE SECOND ARECIBO SEARCH FOR 5 GHz RADIO FLARES FROM ULTRACOOL DWARFS

Route

Wolszczan

2016

ApJ

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We describe our second installment of the 4.75 GHz survey of ultracool dwarfs (UCDs) conducted with the Arecibo radio telescope, which has observed 27 such objects and resulted in the detection of sporadic flaring from the T6 dwarf, WISEPC J112254.73+255021.5. We also present follow up observations of the first radio-emitting T dwarf, 2MASS J10475385+2124234, a tentatively identified radio emitting L1 dwarf, 2MASS J1439284+192915, and the known radio-flaring source, 2MASS J13142039+132011 AB. Our new data indicate that 2MASS J1439284+192915 is not a radio flaring source. The overall detection rate of our unbiased survey for radio-flaring UCDs is ∼5% for new sources, with a detection rate for each spectral class of ∼5-10%. Evidently, radio luminosity of the UCDs does not appear to monotonically decline with spectral type from M7 dwarfs to giant planets, in contradiction to theories of the magnetic field generation and internal structure of these objects. Along with other, recently published results, our data exemplify the unique value of using radio surveys to reveal and study properties of substellar magnetic activity.

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“…This is clear evidence that the physical mechanisms for the radio and X-ray emissions operating in an early B-star like HR 7355 are distinct from coronal mechanisms operating in the intermediate-and low-mass main sequence stars. Yet, somewhat surprisingly, the deviation of the early type HR 7355 from the Guëdel-Benz relation is similar to that for the stars at the bottom of the main sequence -the ultra cool dwarfs with spectral type later than M7 (Berger et al 2010;Williams, Cook & Berger 2014;Lynch et al 2016). These important similarities between active ultra cool dwarfs and a strongly magnetic B star indicate that radio and X-ray emission in their magnetospheres may be produced by related physical mechanisms and provide useful hints for the latter.…”

Section: X-ray Diagnosticmentioning

confidence: 55%

The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae

Leto

Trigilio

Oskinova

et al. 2017

Monthly Notices of the Royal Astronomical Society

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In this paper we investigate the multiwavelengths properties of the magnetic early B-type star HR 7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM-Newton X-ray telescope. Modeling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR 7355 magnetosphere. A comparison between HR 7355 and a similar analysis for the Ap star CU Vir, allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR 7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR 7355 and is likely relevant for magnetospheres of other magnetic early type stars.

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Radio detections of southern ultracool dwarfs

Cited by 35 publications

References 62 publications

Modelling the environment around five ultracool dwarfs via the radio domain

Modelling the environment around five ultracool dwarfs via the radio domain

THE SECOND ARECIBO SEARCH FOR 5 GHz RADIO FLARES FROM ULTRACOOL DWARFS

The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae

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