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Astron. Astrophys. 335, 379-387 (1998)

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Limits on MACHOs from microlensing in the double quasar Q0957+561

Robert Schmidt and Joachim Wambsganss

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany

Received 22 January 1998 / Accepted 12 March 1998


The light curves of the two images of the double quasar Q0957+561 as obtained by Kundic et al. (1997) are almost identical, except for an overall time delay and scaling factor. This allows us to put limits on the amount of microlensing that took place during the time interval corresponding to the monitoring observations. We perform numerical simulations in which we model the microlensing behaviour of the (halo of the) lensing galaxy in the system. We test "MACHO-masses" ranging from 10 to 10 [FORMULA] and quasar sizes from 10 to 3 cm. Statistically comparing the expected microlensing-induced changes from 100 000 simulated light curves over a period of 160 days with the (lack of) observed fluctuations, we can constrain regions in the parameter space of MACHO mass and quasar size with various degrees of confidence. In particular, a halo consisting of objects at the low end of our mass scale can be ruled out with high confidence for a small quasar size. A halo consisting of objects with 10 or 10 [FORMULA] cannot be ruled out yet, but it should produce MACHO induced fluctuations in future observations. We also test halos with only 50% or 25% of the mass in compact objects; constraints here are a bit less stringent.

Key words: gravitational lensing – dark matter – quasars: individual: Q0957+561 – methods: numerical

Send offprint requests to: R. Schmidt, (rschmidt@aip.de)

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© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998