EDP Sciences
Free access
Volume 499, Number 3, June I 2009
Page(s) 649 - 652
Section Astrophysical processes
DOI http://dx.doi.org/10.1051/0004-6361/200912034
Published online 08 April 2009
A&A 499, 649-652 (2009)
DOI: 10.1051/0004-6361/200912034

Research Note

23 GHz VLBI observations of SN 2008ax

I. Martí-Vidal1, 2, J. M. Marcaide1, A. Alberdi3, J. C. Guirado1, M. A. Pérez-Torres3, E. Ros2, 1, I. I. Shapiro4, R. J. Beswick5, T. W. B. Muxlow5, A. Pedlar5, M. K. Argo6, S. Immler7, N. Panagia8, 9, 10, C. J. Stockdale11, R. A. Sramek12, S. Van Dyk13, and K. W. Weiler14

1  Dpt. Astronomia i Astrofísica, Universitat de València, C/ Dr. Moliner 50, 46100 Burjassot, Spain
    e-mail: I.Marti-Vidal@uv.es
2  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3  Instituto de Astrofísica de Andalucía (CSIC), C/ Camino bajo de Huétor 50, 18008 Granada, Spain
4  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 51, Cambridge, MA 02138, USA
5  Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK
6  Department of Imaging and Applied Physics, Curtin University of Technology, Bentley, WA 6845, Australia
7  NASA Goddard Space Flight Center, Astrophysics Science Division, Code 662, Greenbelt, MD 20771, USA
8  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA
9  INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123, Catania, Italy
10  Supernova Ltd, OYV #131, Northsouth Rd., Virgin Gorda, British Virgin Islands
11  Department of Physics, Marquette University, PO Box 1881, Milwaukee, WI 53201-1881, USA
12  National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
13  University of California, Astronomy Department, Berkeley, California 94720, USA
14  Naval Research Laboratory, Code 7210, Washington, DC 20375-5320, USA

Received 10 March 2009 / Accepted 24 March 2009

We report on phase-referenced 23 GHz Very-Long-Baseline-Interferometry (VLBI) observations of the type IIb supernova SN 2008ax, made with the Very Long Baseline Array (VLBA) on 2 April 2008 (33 days after explosion). These observations resulted in a marginal detection of the supernova. The total flux density recovered from our VLBI image is 0.8 $\pm$ 0.3 mJy (one standard deviation). As it appears, the structure may be interpreted as either a core-jet or a double source. However, the supernova structure could be somewhat confused with a possible close by noise peak. In such a case, the recovered flux density would decrease to 0.48 $\pm$ 0.12 mJy, compatible with the flux densities measured with the VLA at epochs close in time to our VLBI observations. The lowest average expansion velocities derived from our observations are (1.90 $\pm$ 0.30) $\times$ 105 km s-1 (case of a double source) and (5.2 $\pm$ 1.3) $\times$ 104 km s-1 (taking the weaker source component as a spurious, close by, noise peak, which is the more likely interpretation). These velocities are 7.3 and 2 times higher, respectively, than the maximum ejecta velocity inferred from optical-line observations.

Key words: galaxies: individual: NGC 4490 -- radio continuum: stars -- supernovae: individual: SN 2008ax -- supernovae: general

© ESO 2009