Search for the elusive optical counterpart of PSR J0537–6910 with the HST Advanced Camera for Surveys

We present the results of deep, high-resolution, multi-band optical observations of the field of the young (∼ 5, 000 yrs) 16 ms X-ray pulsar PSR J0537−6910 performed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). Although a few new potential counterparts have been detected within or close to the revised Chandra X-ray error circle (≃ 1′′) of the pulsar, only two of them (with magnitudes m814W ≈ 23.9 and m814W ≈ 24.2) show indications of a peculiar spectrum which could be related to optical emission from the pulsar. This might be true also for a third, fainter, candidate detected only in one filter (with magnitude m814W ≈ 26.7). If either of the two brighter candidates is indeed the actual counterpart, the optical output of PSR J0537−6910 would make it similar to young Crab-like pulsars. If not, it would mean that PSR J0537−6910 is significantly underluminous with respect to all pulsars detected in the optical.