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Published August 11, 1988 | public
Journal Article

Probable optical counterpart of the eclipsing millisecond pulsar system, 1957 + 20

Abstract

Following the discovery of an eclipsing, millisecond pulsar 1957+20 (ref. 1) we conducted a series of optical observations to identify the optical counterpart of the system. We report the detection of a probably variable object (hereafter star X) with a mean apparent V magnitude of ∼20 within the astrometric error circle of the equatorial radio position of the pulsar. Star X appears fainter at orbital phase 0.21, the onset of the pulsar eclipse, compared with the quadrature position, suggesting that it is probably the optical counterpart. We argue that the secondary heated by the pulsar wind and not the pulsar itself makes the dominant contribution to the visible radiation from this system. The absolute magnitude of star X is M_v ≈ 10.5, assuming a distance of ∼ 0.8 kpc derived from the dispersion measure. The optical luminosity of the counterpart directly measures the fraction of the pulsar wind power responsible for heating the secondary. Future optical observations may be able to constrain the nature of the pulsar wind.

Additional Information

© 1988 Nature Publishing Group. Received 23 May; accepted 8 July 1988. We thank M. Shara and the other members of the Hubble Space Telescope Guide Star Project for permission to use the Guide Star Catalog, R. Lucas and D. Rehner for help in extracting the astrometric data of the secondary stars, J. Schombert for help in digitizing at the Jet Propulsion Laboratory, J. Cohen for obtaining the earlier CCD images, and R. J. Rand, J. M. Hester and the staff at Palomar Observatory for assistance with the observations. The Palomar 60-in telescope is operated jointly by the California Institute of Technology and the Carnegie Institution of Washington. This work was supported in part by the California Institute of Technology.

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023