Why did the hybrid Phillips Curve become flatter (as empirical data shows) after the crisis? The Phillips Curve equation is:
$$\pi_t=\pi_t^e + \beta_1 (\beta_2 Y_t + (1-\beta_2) Z_t) + \varepsilon_t^\pi$$
where $\pi_t$ is the inflation, $\pi_t^e$ is the expected inflation, $Y_t$ is the output level, $Z_t$ is the real exchange rate, and $\varepsilon_t^\pi$ is a stochastic shock.

In a small open economy (semi-structural framework), the impulse response functions to a domestic demand shock are the following:



After the crisis, the Phillips Curve became flatter. My question is, how can one interpret the change in the slope of the Phillips Curve after the crisis?
(1) The Phillips curve is not a structural thing, it is not surprising that the relationship between unemployment and inflation is not constant over time.

(2) There's a nice AER paper by Simon Gilchrist and coauthors that argues that inflation did not go down as much as in earlier recessions because financially constrained firms needed to keep their cash-flows up and increased prices.