Observation and Data Reduction of the Brown Dwarf 2MASSW J0746425 + 200032 by Five-Hundred-Meter Aperture Spherical Radio Telescope

Round 1

Reviewer 1 Report

I recommend publication of this significant new work. The authors use the unparalleled capabilities of the FAST radio telescope to investigate a nearby ultracool dwarf binary. This particular system is known to have radio flares at other frequencies and is a key example of magnetic activity near the end of the main sequence.  The authors present their work in detail, very clearly. The monitoring lasts for more than one period, so the work had the opportunity to detect at least one flare; they include comparison to FAST observations of AD Leo flares.  Although they conclude that they have not detected any flares from this system, the work is significant and deserves to be published. This kind of work is essential for progress in astronomy. The authors suggest some future followups and I expect that they -- or others -- will continue this research.

Suggested minor edits:

Line 16. Delete “about”

Line 27 “closed” -> “close”

Line 44. “is” -> “was”

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

I am quite surprising that reliable registration of flaring radio emission from 2MASSWJ0746425+200032 in the L-band was unsuccessful although for observations the FASТ with unprecedented sensitivity was used. Moreover, it is well-known that the flare activity of binary stars is higher than that of single stars. A striking example is the flaring activity of RS CVn. Observations have shown that at frequencies above 4 GHz besides flaring radio radiation the quiescent and persistent radio emission from ultra-cool dwarfs were really observed (e.g., Osten et al. ApJ, 637:518, 2006; Berger et al. ApJ, 695:310, 2009).

It is possible that the surprising non-detection is due to the limited time of observations (2.45 hours) keeping in mind the typical period of radiation of ultra-cool stars (~2 hours). Another reason can be a plasma parameters and magnetic field doesn’t fit to the radiation mechanism. Any way this result is in the favour of positive slope in the frequency spectrum between 1.5 GHz and 4 GHz.

As for the ECM emission discussed by authors, there is serious restriction dealing with escape conditions of cyclotron maser radiation from the stellar coronae. Indeed, the emission generated at the fundamental and the second harmonic of the electron cyclotron frequency should absorbed in the stellar corona at the second and the third cyclotron harmonic layers (e.g., Stepanov et al. A&A 299:739, 1995). X ray observations (e.g.,Berger et al. ApJ 709:332, 2010) indicate a high temperature of coronae of brown dwarfs, which contributes to the cyclotron absorption of ECM radiation. So, there are only two quite narrow “parallel” and “perpendicular” windows for escaping of ECM emission trough the stellar coronae for o-mode and “parallel” window only for x-mode. If there is no proper radiation pattern in the emission source, no ECM radiation will be observed. Hence, except of ECM radiation the thermal bremstrahlung, gyrosynchrotron, and plasma radiation mechanisms should considered in that context. I’d like to wish the authors also to turn besides the multi-wavelength radio observations, also to the X-ray emission data of brown dwarfs.

Nevertheless, the extensive preparatory work done on the new 500-m radio telescope is quite useful for further study of the origin of radio emission from ultra-cool stars, in particular, to investigate the frequency spectrum of radio radiation of brown dwarfs. I’d like recommend to publish this manuscript in the Universe.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf