Can someone tell how to estimate the pole zero in the bandgap  circuit (2)shown here. Please point me to any references dealing with stability analysis of bandgap circuits (pole zero estimation)

I dont understand the need/advantage of using the additional resistors r1 and r3 in the fig (2)
In fig (2) can we also take the o/p reference at the other end (above resistor r1)? If so which one is better ?

Thanks,
vamshi