Search for the Optical Counterpart of PSR 1953+29

Extract

1) PSR B1953+29, the first millisecond binary pulsar discovered, has a low mass companion with a long orbital period (see parameters in Table 1).

2) Shortly after its discovery the averaged pulse profile was observed to change shape in a discrete fashion: two different pulse profiles were alternating (Boriakoff et al 1986). Each pulse profile remained the same for typical times of days. This is reminiscent of the mode-changing behaviour of slower pulsars, however, normally such pulsars remain in one mode for only a few minutes.

3) Observations with a Cherenkov TeV Gamma-Ray detector have shown a large pulse-profile peak when the data is folded with the correct pulse period. Recent reprocessing of the original data shows the same peak (Bowden et al 1990).

4) Comparison with optical photographs revealed a bright star (20-th magnitude) located less than 1 arcsec from the pulsar positions determined with the VLA and from timing. A star of ∼O.2M_⊙ is expected to be a white dwarf, at the distance of 3.5-5kpc it would be invisible.

5) Optical spectral observations of the star with the 5-meter Palomar telescope showed a reddened spectrum without any emission or absorption lines. This is typical of very hot objects.

6) CCD images obtained with the Russian 6 meter optical telescope in the Caucasus were taken to pinpoint the location of the star with accuracies better than a small fraction of an arc second. Imperfections of the CCD star images (saturation, etc.), in particular for bright 15-18 magnitude stars, had to be taken into account to pinpoint the center of the observed image. A technique was developed for finding the center of the image with an accuracy better than 0.17 arcsec, a single pixel of the CCD image. Arcs of ellipses were fitted to cross-sections of the star image at different light intensity levels. Down to very low light levels no pulsation was found.