A Possible Optical Counterpart for the Triple Pulsar System PSR B1620-26
  We have searched deep optical images of the globular cluster M4 for a possible optical counterpart for the third body in the PSR B1620-26 system. We identify as a possible optical counterpart a star located within $0.3''$ of the nominal pulsar position with $V\approx 20$. This magnitude is consistent with a main sequence cluster member with $M\approx 0.45M_\odot$. However, this star may be blended with fainter stars, and the probability of a chance superposition is non-negligible. 
C. D. Bailyn, E. P. Rubenstein, T. M. Girard, D. Dinescu, F. A. Rasio,   and B. Yanny