Let $f: X \to Y$ be a locally trivial fibration between locally compact spaces with fiber $F$. It is well known that for a constant sheaf $A\_X$ on $X$, the higher direct images $R^n f\_\* A\_X$ are locally constant, with stalk $H^n(F, A)$. This can be seen from the description of said higher direct images as the sheaf associated to the presheaf
$$ U \mapsto H^n(f^{-1}(U), A\_X|\_{f^{-1}(U)}). $$


According to Iversen, *Cohomology of Sheaves*, Theorem VII.1.4, the stalks of the higher direct images with compact support have a similar description (for an arbitrary continuous map $f: X \to Y$ and an arbitrary sheaf $\mathcal{F}$)
$$ (R^n f\_! \mathcal{F})\_y = H^n\_c(f^{-1}(y), \mathcal{F}). $$


My question is then: if $f$ is a locally trivial fibration, does the same result hold? That is, are the sheaves $R^n f\_! A\_X$ local systems on Y? The same method of proof will not do, since the analogous candidate for a presheaf does not have well-defined restriction maps. And if you try to modify the proof that Iversen gives for the result on the stalks, things seem to break down from the begining, so I don't know how I could prove this.




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**UPDATE:** Since we want to prove a local result, we may assume that we have a trivial fibration $B \times F \to B$. Using proper base change on the diagram
$$ \newcommand{\da}[1]{\left\downarrow{\scriptstyle#1}\vphantom{\displaystyle\int\_0^1}\right.}
\begin{array}{ccc}
B \times F & \xrightarrow{\pi\_1} & B \\
\da{\pi\_2} & & \da{a\_B} \\
F & \xrightarrow{a\_F} & \{\*\}
\end{array}$$
gives an isomorphism
$$ a\_B^\* \circ R^n a\_{F,!} (A\_F) \cong R^n \pi\_{1,!} \circ \pi\_2^\* (A\_F), $$
which by adjointness gives a map
$$ H^n\_c(F, A) = R^n a\_{F,!} (A\_F) \to a\_{B,\*} \circ R^n \pi\_{1,!} \circ \pi\_2^\* (A\_F) = \Gamma(B, R^n \pi\_{1,!} (A\_{B\times F})). $$
This map should be an isomorphism if the result were true (it is equivalent to the result) but I don't see how to prove that it actually is an isomorphism.



Higher direct image with compact support of a constant sheaf
With the information added in the last update, the result is already proved once you realize that the unit of the adjunction
$$ id \to a\_{B,\*} a\_B^\* $$
is actually an isomorphism on the category of abelian groups if the space $B$ is connected.


