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Hipparcos positioning of Geminga: how and why

Hipparcos positioning of Geminga: how and why

Publication date: 05 January 1998

Authors: Caraveo, P. A., Lattanzi, M. G., et al.

Journal: A&A
Volume: 329
Page: L1-L4
Year: 1998

Copyright: A&A

Accuracy in the absolute position in the sky is one of the limiting factors for pulsar timing, and timing parameters have a direct impact on the understanding of the physics of Isolated Neutron Stars (INS). We report here on a high-accuracy measurement of the optical position of Geminga (mv=25.5), the only known radio-quiet INS. The procedure combines the Hipparcos and Tycho catalogues, ground-based astrometric data,and Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC2) images, to yield Geminga's absolute position to within ~ 40 mas (per coordinate). Such a positional accuracy, unprecedented for the optical position of a pulsar or an object this faint, is needed to combine in phase gamma -ray photons collected over more than 20 years, i.e. over 2.5 billions of star' revolutions. Although quite a difficult task, this is the only way to improve our knowledge of the timing parameters of this radio silent INS. Based on Observation with the ESA Hipparcos satellite.

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