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Microlensing on different timescales in the lightcurves of QSO 0957+561 A,B
J. Pelt 1, 5,
R. Schild 2, 5,
S. Refsdal 3, 5 and
R. Stabell 4, 5
Received 20 February 1998 / Accepted 26 May 1998
A statistical analysis of an extended data set on a time basis of 17 years of optical observations of the gravitationally lensed quasar 0957+561 is presented. We use all available photometry to estimate the time delay between A and B images as days. Using this refined value we investigate basic statistical properties of the difference curve between the A and the time shifted B image. We find a significant variability of 0.25 mag on a time scale of 5 years, which we interpret as microlensing by compact objects in the lensing galaxy.
We show that masses down to about may explain this microlensing event. Solar mass objects alone can more or less be excluded. However, a distribution of compact objects with a small fraction () in solar mass objects, seems to be possible. The best constrained parameter is the radius of the source which roughly should be (within a factor of 3).
With the present noise level an additional variability due to the microlensing on shorter time scales (days to months) is difficult to prove with a reasonable significance. All steps of the analysis are carried out by using simple statistical tests and with as few a priori assumptions as possible.
Key words: methods: statistical methods: data analysis quasars: individual: 0957+561A,B gravitational lensing
Send offprint requests to: R. Stabell4
Online publication: July 27, 1998