A Large Brightness Enhancement of the QSO 0957+561 A Component

Oscoz, A.; Alcalde, D.; Serra-Ricart, M.; Mediavilla, E.; Muñoz, J. A.
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The Astrophysical Journal, Volume 573, Issue 1, pp. L1-L4.

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We report an increase of more than 0.2 mag in the optical brightness of the leading image (A) of the gravitational lens Q0957+561, detected during the 2000 September to 2001 June monitoring campaign (2001 observing season). The brightening is similar to or even greater than the largest change ever detected during the 20 yr of monitoring of this system. We discuss two different provisional explanations of this event: intrinsic source variability or microlensing (either short-timescale microlensing or cessation of the historical microlensing). An exhaustive photometric monitoring of Q0957+561 is needed until the summer of 2002 and during 2003 to discriminate between these possibilities.