Microlensing neutron stars

¹ Institut für Theoretische Physik, Technische Universität Wien, Wiedner Hauptstraße 8–10, 1040 Wien, Austria e-mail: dschwarz@hep.itp.tuwien.ac.at
² Institut für Theoretische Physik, J. W. Goethe-Universität, 60054 Frankfurt am Main, Germany e-mail: seidel@th.physik.uni-frankfurt.de

Corresponding author: D. J. Schwarz, dschwarz@hep.itp.tuwien.ac.at

Received: 27 March 2001
Accepted: 28 March 2002

Abstract

We investigate the chances that neutron stars act as the lens in a gravitational microlensing event towards the galactic bulge or a spiral arm. The observation of neutron stars by means of gravitational microlensing would allow the estimation of neutron star masses independently of the property of being a pulsar in a binary system. We estimate the contribution of neutron stars to the optical depth and the lensing rate based on two different models of pulsar distribution in the galaxy. Since only a small fraction of all neutron stars are pulsars, it is unlikely to find a pulsar that acts as a microlens by chance. A position comparison of known radio pulsars with observed microlensing candidates towards the galactic bulge and spiral arms shows no candidate pairs, which is consistent with the theoretical expectation. To improve the probability of microlensing a pulsar, we suggest a search for gravitational microlensing events of known nearby high proper motion pulsars. The pulsar PSR J1932+1059 is a good candidate for an astrometric detection of gravitational lensing.