We present wide-field imaging of the 2007 outburst of Comet 17P/Holmes obtained serendipitously by SuperWASP-North on 17 nights over a 42-night period beginning on the night ( 2007 October 22-23 ) immediately prior to the outburst .
Photometry of 17P ’ s unresolved coma in SuperWASP data taken on the first night of the outburst is consistent with exponential brightening , suggesting that the rapid increase in the scattering cross-section of the coma could be largely due to the progressive fragmentation of ejected material produced on a very short timescale at the time of the initial outburst , with fragmentation timescales decreasing from t _ { frag } \sim 2 \times 10 ^ { 3 } s to t _ { frag } \sim 1 \times 10 ^ { 3 } s over our observing period .
Analysis of the expansion of 17P ’ s coma reveals a velocity gradient suggesting that the outer coma was dominated by material ejected in an instantaneous , explosive manner .
We find an expansion velocity at the edge of the dust coma of v _ { exp } = 0.55 \pm 0.02 km s ^ { -1 } and a likely outburst date of t _ { 0 } = 2007 ~ { } { October } ~ { } 23.3 \pm 0.3 , consistent with our finding that the comet remained below SuperWASP ’ s detection limit of m _ { V } \sim 15 mag until at least 2007 October 23.3 .
Modelling of 17P ’ s gas coma indicates that its outer edge , which was observed to extend past the outer dust coma , is best explained with a single pulse of gas production , consistent with our conclusions concerning the production of the outer dust coma .