-3 -Multiple outbursts of a Jupiter-family comet, 15P/Finlay, occurred from late 2014 to early 2015. We conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 January 15.6-15.7. The gas, consisting mostly of C 2 and CN, and dust particles expanded at speeds of 1,110 ± 180 m s −1 and 570 ± 40 m s −1 at a heliocentric distance of 1.0 AU. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity β max = 1.6 ± 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 10 8 -10 9 kg of dust particles (assumed to be 0.3 µm-1 mm) were ejected through each outburst. Although the total mass is three orders of magnitude smaller than that of the 17P/Holmes event observed in 2007, the kinetic energy per unit mass (10 4 J kg −1 ) is equivalent to the estimated values of 17P/Holmes and 332P/2010 V1 (Ikeya-Murakami), suggesting that the outbursts were caused by a similar physical mechanism. From a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15P/Finlay-class outbursts occur >1.5 times annually and inject dust particles from Jupiter-family comets and Encke-type comets into interplanetary space at a rate of ∼10 kg s −1 or more.
The Orionid outburst observed in 2006 resulted in strong activity, continuing for about four days. We have found that this activity was caused by the dust trails formed by meteoroids ejected from 1P/Halley in $-$1265, $-$1197, and $-$910. These meteoroids had six times the Jovian orbital period, and their orbit was able to intersect the Earth’s orbit at the present day because of this mean motion resonance with Jupiter.
Using a prototype of the Tomo-e Gozen wide-field CMOS mosaic camera, we acquire widefield optical images at a cadence of 2 Hz and search them for transient sources of duration 1.5 to 11.5 seconds. Over the course of eight nights, our survey encompasses the equivalent of roughly two days on one square degree, to a fluence equivalent to a limiting magnitude about V = 15.6 in a 1-second exposure. After examining by eye the candidates identified by a software pipeline, we find no sources which meet all our criteria. We compute upper limits to the rate of optical transients consistent with our survey, and compare those to the rates 2 expected and observed for representative sources of ephemeral optical light.
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