Rapid brightness fluctuations in Q0957+561A,B: Microlensing or seeing?

Wesley N. Colley, Irwin I. Shapiro, Jennifer Pegg, Edwin L. Turner, Tomislav Kundić, Karen Loomis, N. C. Hastings, Russet McMillan

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We address the following question: How does one reliably distinguish rapid microlensing events from atmospheric or instrumental effects on observed brightness fluctuations of distant objects? Our approach was to do a controlled, albeit limited, experiment, the first of its kind: observe Q0957+561A,B simultaneously through filters of the same characteristics with two telescopes with comparable fields of view but separated sufficiently for atmospheric fluctuations to be independent. Over the 1998-1999 viewing season, we succeeded in obtaining simultaneous data on 14 of the 55 nights scheduled. Analysis of these data led to the following: (1) after correction for "blending" of the A and B images, most rapid microlensing candidate outliers disappeared, and the agreement of the photometry from the two telescopes improved to an rms difference of about 15 mmag; (2) no microlensing events of amplitude greater than 0.1 mag were observed in either data set over the entire run, nearly ruling out ∼10-5 M MACHOs as composing more than about half the dark matter in the lens galaxy, if the source size is ≲3 × 1014 cm.

Original languageEnglish (US)
Pages (from-to)711-715
Number of pages5
JournalAstrophysical Journal
Issue number2 I
StatePublished - May 10 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Dark matter
  • Galaxies: halos
  • Gravitational lensing
  • Methods: data analysis
  • Techniques: photometric


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