Precision Photometry for Q0957+561 Images A and B

Abstract

Since the persuasive determination of the time-delay in Q0957+561, much interest has centered around shifting and subtracting the A and B light-curves to look for residuals due to microlensing. Solar mass objects in the lens galaxy produce variations on timescales of decades, with amplitudes of a few tenths of a magnitude, but MACHO's (with masses of order $10^{-3}$ to $10^{-7}{M}_{\odot }$) produce variations at only the 5% level. To detect such small variations, highly precise photometry is required. To that end, we have used 200 observations over three nights to examine the effects of seeing on the light-curves. We have determined that seeing itself can be responsible for correlated 5% variations in the light-curves of A and B. We have found, however, that these effects can be accurately removed, by subtracting the light from the lens galaxy, and by correcting for cross contamination of light between the closely juxtaposed A and B images. We find that these corrections improve the variations due to seeing from 5% to a level only marginally detectable over photon shot noise (0.5%).

21 Pages with 9 PostScript figures, AASTeX 4 (preprint style)

References in corpus (1)

• Improved Parameters and New Lensed Features for Q0957+561 from WFPC2 Imaging

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• New aperture photometry of QSO 0957+561; application to time delay and microlensing
• Anomalous Fluctuations in Observations of Q0957+561 A,B: Smoking Gun of a Cosmic String?
• Hourly Variability in Q0957+561
• GLITP Optical Monitoring of QSO 0957+561: VR Light Curves and Variability
• 'Round the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar