In public website images obtained by the SWAN experiment onboard of the SOHO spacecraft between Mar. 5 and 8 and again beginning on Mar. 16 R. Matson discovered an object, that moved through the constellations Pegasus and Andromeda, while significantly brightening. Michael Jäger succeeded on Mar. 24 to take an image of comet C/2015 F3 (SWAN) with his 10"-reflector. The comet was of magnitude 10-11, showing a diffuse 2' coma and a 10' tail pointing to the North. On Mar. 26 Alan Hale could observe the comet visually: his estimate quoted the comet to be of magnitude 10.3, showing a 2.3' coma. The comet passed perihelion already on Mar. 9 at a solar distance of 0.84 AU (CBET 4084). Assuming an average evolution the comet should fade slowly during the next weeks, but should be brighter than 16.0 mag until July. During this interval it will move through the constellations Cassiopeia, Cepheus, Camelopardalis, Draco, Ursa Major into Coma Berenices, thereby passing the North Pole at a distance of only 3° at the end of April.
The comet faded rapidly. According to 12 visual and photovisual observations by 3 members of the German Comet Section and 30 international observations the fading can be rather well described by the parameters m0=10.2 mag / n=8. Thus the comet should have been of magnitude 9.4 mag both at perihelion and at the time of the first terrestrial observation (Mar. 24). In mid-May the brightness had already faded 13.5 mag.
Total Brightness and Coma Diameter
In parallel of the fading the coma diameter decreased from 4.5' (190.000 km) to 1.5' (40.000 km) with the coma getting more and more diffuse (DC 3 to DC 0). Visual tail observations have not been reported.
Andreas Kammerer
