Summary: Astronomy & Astrophysics manuscript no. preprint c ESO 2007
July 6, 2007
LETTER TO THE EDITOR
Sporadic Long-term Variability in Radio Activity from a Brown
A. Antonova1, J.G. Doyle1, G. Hallinan2, A. Golden2 and C. Koen3
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
Computational Astrophysics Laboratory, I.T. Building, National University of Ireland, Galway, Ireland
Department of Statistics, University of the Western Cape, Private Bag X17, Bellville, 7535 Cape, South Africa
Context. Radio activity has been observed in a large variety of stellar objects, including in the last few years, ultra-cool dwarfs.
Aims. To explore the extent of long-term radio activity in ultra-cool dwarfs.
Methods. We use data taken over an extended period of 9 hr from the Very Large Array of the source 2MASS J05233822-1403022
in September 2006, plus data taken in 2004.
Results. The observation taken in September 2006 failed to detect any radio activity at 8.46 GHz. A closer inspection of earlier data
reveals that the source varied from a null detection on 3 May 2004, to 95 µJy on 17 May 2004, to 230 µJy on 18 June 2004. The
lack of detection in September 2006 suggests at least a factor of ten flux variability at 8.46 GHz. Three short photometric runs did not