Answer
$I=4.8\times 10^{-29}W/m^2$
Work Step by Step
Converting from light years to meters yields $$(4.3 ly)(3.00\times 10^8m/s)(60.s/min)(60.min/hr)(24hr/day)(365.25days/year)$$ $$=4.07\times 10^{16}m$$ To find intensity at a point, use the formula relating distance and intensity, which is $$I=\frac{P}{A}=\frac{P}{4\pi R^2}$$ Substituting a value of $R=4.07\times 10^{16}m$ and $P=1.0\times 10^6W$ yields $$I=\frac{1.0 \times 10^6 W}{4\pi (4.07\times 10^{16}m)^2}$$ $$=4.8\times 10^{-29}W/m^2$$
