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Astron. Astrophys. 362, L37-L40 (2000)

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Letter to the Editor

Microlensing results from APO monitoring of the double quasar Q0957+561A,B between 1995 and 1998

J. Wambsganss 1,3,4, R.W. Schmidt 1,2, W. Colley 5, T. Kundi 6 and E. L. Turner 7

1 Universität Potsdam, Institut für Physik, Am Neuen Palais 10, 14469 Potsdam, Germany, (jkw@astro.physik.uni-potsdam.de)
2 University of Cambridge, Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK, (rschmidt@ast.cam.ac.uk)
3 Max-Planck-Institut für Gravitationsphysik, Am Mühlenberg 1, 14476 Golm, Germany
4 The University of Melbourne, School of Physics, Parkville, Vic 3052, Australia
5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 USA, (wcolley@barbecue.harvard.edu)
6 Renaissance Technologies, 600 Route 25A, East Setauket, NY 11733, USA, (tomislav@rentec.com)
7 Princeton University Observatory, Peyton Hall, Princeton, NJ 08544, USA, (elt@astro.princeton.edu)

Received 29 September 2000 / Accepted 10 October 2000

Abstract

If the halo of the lensing galaxy 0957+561 is made of massive compact objects (MACHOs), they must affect the lightcurves of the quasar images Q0957+561 A and B differently. We search for this microlensing effect in the double quasar by comparing monitoring data for the two images A and B - obtained with the 3.5m Apache Point Observatory from 1995 to 1998 - with intensive numerical simulations. This way we test whether the halo of the lensing galaxy can be made of MACHOs of various masses. We can exclude a halo entirely made out of MACHOs with masses between [FORMULA] and [FORMULA] for quasar sizes of less than [FORMULA] cm, hereby extending previous limits upwards by one order of magnitude.

Key words: galaxies: halos – cosmology: observations – cosmology: dark matter – cosmology: gravitational lensing

Send offprint requests to: J. Wambsganss

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 2000
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