The other alternative is a satellite. I've seen naked-eye satellites flare brightly and expand in size due to outgassing while in orbit. Alternatively I've also seen satellites re-entering that flared for about that period of time - tens of seconds. The only unusual thing is it was due west while satellites tend to orbit in an inclined plane, so no lateral movement is a problem for that explanation - though not impossible.
Or a military jet on full afterburner, maybe scrambled to intercept the jet that apparently turned off its transponder?