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Radio detections of KT Eri

ATEL # 2434; T.J. O'Brien (Manchester), T.W.B. Muxlow (Manchester), J. Stevens (CSIRO), A. Datta (New Mexico Tech/ AOC, NRAO), N. Roy (AOC, NRAO), S.P.S Eyres (Central Lancashire), M.F. Bode (Liverpool JMU)
on 11 Feb 2010; 19:30 UT
Password Certification: Tim O'Brien (tim.obrien@manchester.ac.uk)

Subjects: Radio, Cataclysmic Variables, Nova

We report radio observations of KT Eri (Nova Eri 2009) using ATCA, GMRT, MERLIN and VLA. KT Eri (RA: 04:47:54.21, Dec: −10:10:43.1, J2000) was discovered on 2009 November 25 but was present in outburst on sky patrol images taken on 2009 Nov 14 (IAUC # 9098 ). It is currently in the super-soft source phase of X-ray emission and is being intensively monitored with the Swift X-ray Telescope (ATEL #2423, ATEL #2392).

At radio wavelengths we have had several epochs of Target of Opportunity observations with ATCA, GMRT, MERLIN and VLA. The first observations took place with MERLIN at 5 GHz using Director's Discretionary Time (DDT) between 2009 Dec 4-8 (days 20-24 after outburst). The source was not detected at a 3-sigma upper limit of 0.18 mJy. It was then observed with VLA at 5 and 1.4 GHz on Dec 28 (day 44) as a Rapid Response observation. This resulted in the first (>6-sigma) radio detection of this nova at 5 GHz with a peak flux of 0.21 mJy. At 1.4 GHz, the 3-sigma upper limit on the flux density was 0.5 mJy. DDT observations with GMRT at 610 MHz on 2010 Jan 10 (day 57) led to a 3-sigma upper limit of 1.0 mJy. A further sequence of MERLIN DDT observations took place between Jan 13-18 (days 60-65) at 5 GHz. This resulted in a 4-sigma detection with a flux density of about 0.33 mJy. Following this, there have been two epochs of Target of Opportunity observations with ATCA. On Jan 24 (day 71) the flux density was 0.56 mJy in a band centred at 5.5 GHz and 0.85 mJy at 9 GHz. On Feb 3 (day 81) the source had brightened to 0.74 mJy (5.5 GHz), 1.41 mJy (9 GHz) and 2.27 mJy (17 GHz).

Radio observations provide important information on the ejected mass and geometry, often not well-determined using other methods. Standard models predict free-free radio emission from the expanding nova ejecta (although in some novae we also expect non-thermal radio emission from shock interactions). Initially optically thick, the flux density increases as the source expands but then turns over as it becomes optically thin; the timescales depending on the ejecta mass and velocity. Our observations show we have caught this nova on the rising part of the radio light curve.

ATCA, GMRT and MERLIN observations are continuing and further observations, particularly at other wavelengths, are strongly encouraged.


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