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THE ASTRONOMER Electronic Circular No 2446      2008 May 17 13.14UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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COMET 46P/WIRTANEN: OUTBURST
Mark Kidger (European Space Agency, European Space Astronomy Centre) 
reports on behalf of the "Observadores_cometas" group that 46P/Wirtanen 
has experienced a significant outburst. Recent R magnitudes in different 
apertures are:

2008 May 06.9: 10", 16.76; 20", 15.75; 30", 15.20 (Francisco Hernandez, 
MPC J24, Tenerife, Spain)
2008 May 12.9: 10", 17.09; 20", 16.10; 30", 15.4.9 (Gustavo Muler, MPC 
J47, Lanzarote, Spain)
2008 May 15.9: 10", 14.96; 20", 14.21; 30", 13.74 (Jose Ramon Vidal, MPC 
945, Gijon, Spain)
2008 May 16.9: 10", 15.11; 20", 14.41; 30", 13.98 (Cesar Piret, MPC
J46, Lanzarote, Spain)

Images and the multi-aperture photometry show that the inner coma has 
become significantly more condensed, with the coma slope changing from 
considerably more extended than 1/r pre-outburst, to being 1/r or 
slightly steeper at the peak of the outburst.

The light curve of the outburst can be found at:
http://www.astrosurf.com/comets/cometas/46p/may_2008_outburst.htm

Images of the current outburst are available at:
http://www.astrosurf.com/comets/cometas/46p/imagenes/46p.html

Observers are strongly encouraged to follow the evolution of this 
apparently unique light curve event in this object, which has shown 
highly consistent light curve behaviour in its previous apparitions.

Background information:
The values of Afrho obtained by the "Observadores_cometas" group during 
the 2007/08 apparition have, up to the current outburst, been identical 
to within about 10% to those obtained during the 2002 apparition at the 
same time relative to perihelion, which themselves show an almost 
identical behaviour to the 1996 apparition (Kidger, 2004, Astron. 
Astrophys., 420, 389-395). In other words, this comet has shown highly 
consistent and reproducible light curve behaviour over its last three 
apparitions.

The comparative values for 2002 and 2008 at current and past epochs are:
2002: T-8d (r=1.06AU), Afrho=170cm; T+61d (r=1.33AU), Afrho=36cm;
T+102d (r=1.66AU), Afrho=11cm
2008: T-7d (r=1.06AU), Afrho=190cm; T+61d (r=1.33AU), Afrho=38cm;
T+103d (r=1.67AU), Afrho=83cm

Guy M Hurst