All error bars are 1sigma unless otherwise noted.
Using NRAO's Very Large Array (VLA), we detected radio emission from the peculiar variable V445 Puppis on 9 September 2001 (MJD 52161), at a level of 9.6 mJy at 8.4 GHz. No emission was present in an image made on 18 January 2001 at the same frequency, to an rms level of 0.071 mJy/beam. The discovery image is shown below:
The radio position (J2000) is
The source was unresolved with an 8.4 GHz beam (on 9sep01) of 7.3x2.8 arcsec. Preliminary reduction of an initial MERLIN run suggests that the source was barely or not at all resolved in mid-September at 5 GHz, with a beam of about 50 mas. A preliminary look at a VLBA observation from mid-September gives uncertain results; we're working on it...
The figure below shows the evolving radio flux density of V445 Puppis. Note the series of radio flares superposed on the overall decay.
The radio spectra are shown below. A power law (as expected for optically-thin synchrotron emission) would appear as a straight line sloping downwards on this plot. Optically-thin thermal (free-free) emission would be roughly flat (nu^{-0.1}). Note that atmospheric effects introduce additional uncertainty in the data above 15 GHz.
The source appears too complicated at present for any but the simplest fits. Broadly speaking it looks to be synchrotron emission with a typical spectral index of order -0.7, modified at low frequencies (1.4 GHz) by strong absorption, and at high frequencies by on-going radio events.
Please send any questions, comments, or suggestions to Michael Rupen at the e-mail address given below.
Last modified 07 December 2001
mrupen@nrao.edu