Using Duhamel's Principle and the Heat Kernel to Solve an IVP

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I need to solve this:

$u_t(x,t)-ku_{xx}(x,t)=xte^{-t^2}$

By using Duhamel's Principle and the Heat Kernel.

So far this is what I've done:

$u_t(x,t)-ku_{xx}(x,t)=xte^{-t^2}$

where u(x,0)=0

$u(x,t)= \int h(x,t-\sigma|\sigma)d\sigma$

is the solution to the IVP

where h solves

$h_t(x,t|\sigma)-kh_xx(x,t|\sigma)=0$ for all t>0

subject to $h(x,0|\sigma)=f(\sigma)$

where I believe $f(\sigma)=y\sigma e^{-\sigma^2}$

and then using the Heat Kernel Method

$h(x,t|\sigma)=\frac{1}{\sqrt{4 \pi k t}}\int y\sigma e^{-\sigma^2} $$e^\frac{-(x-y)^2}{4kt}dy$

where I substitute in z=x-y and therfroe dy=-dz to get

$h(x,t|\sigma)=\frac{1}{\sqrt{4 \pi k t}}\int (z+x)\sigma e^{-\sigma^2} $$e^\frac{-z^2}{4kt}dz$

But I'm not really sure where to go from here? I'd be grateful if anyone could suggest anything