Around the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar II: Results for the second observing season

摘要

We report on an observing campaign in March 2001 to monitor the brightness ofthe later arriving Q0957+561 B image in order to compare with the previouslypublished brightness observations of the (first arriving) A image. The 12participating observatories provided 3543 image frames which we have analyzedfor brightness fluctuations. From our classical methods for time delaydetermination, we find a 417.09 +/- 0.07 day time delay which should be free ofeffects due to incomplete sampling. During the campaign period, the quasarbrightness was relatively constant and only small fluctuations were found; wecompare the structure function for the new data with structure functionestimates for the 1995--6 epoch, and show that the structure function isstatistically non-stationary. We also examine the data for any evidence ofcorrelated fluctuations at zero lag. We discuss the limits to our ability tomeasure the cosmological time delay if the quasar's emitting surface is timeresolved, as seems likely.