An Event in the Light Curve of 0957+561A and Prediction of the 1996 Image B Light Curve

Abstract

CCD photometry of the gravitational lens system 0957+561A,B in the g and r\nbands was obtained on alternate nights, weather permitting, from December 1994\nthrough May 1995 using the Double Imaging Spectrograph (DIS) on the Apache\nPoint Observatory (APO) 3.5-meter telescope. The remote observing and fast\ninstrument change capabilities of this facility allowed accumulation of light\ncurves sampled frequently and consistently. The Honeycutt ensemble photometry\nalgorithm was applied to the data set and yielded typical relative photometric\nerrors of approximately 0.01 magnitudes. Image A exhibited a sharp drop of\nabout 0.1 magnitudes in late December 1994; no other strong features were\nrecorded in either image. This event displays none of the expected generic\nfeatures of a microlensing-induced flux variation and is likely to be intrinsic\nto the quasar; if so, it should also be seen in the B image with the lensing\ndifferential time delay. We give the expected 1996 image B light curves based\non two values of the time delay and brightness ratio which have been proposed\nand debated in the literature. Continued monitoring of the system in the first\nhalf of 1996 should easily detect the image B event and thus resolve the\ntime-delay controversy.\n