A unique UV flare in the optical light curve of the quasar J004457.9+412344

¹ Thüringer Landessternwarte Tautenburg, Germany
² Max-Planck-Institut für extraterrestrische Physik Garching, Germany
³ Max-Planck-Institut für Astronomie Heidelberg, Germany
⁴ University of Washington, Seattle, USA
⁵ University of Athens, Greece
⁶ University of Roma La Sapienza, Italy
⁷ Christian-Albrechts-Universität Kiel, Germany
⁸ University Bern, Switzerland
⁹ Sternwarte Sonneberg, Germany
¹⁰ University Leipzig, Germany

^a e-mail: meus@tls-tautenburg.de

Abstract

We found that the nova candidate J004457.9+412344 is a radio-quiet quasar at z ∼ 2. Its optical long-term light curve, covering more than half a century, shows quasar typical flux variations superimposed by a spectacular single flare lasting more than one year (observer frame). We could not find comparable light curves among the several thousand catalogued radio-quiet quasars in the stripe 82 of the Sloan Digital Sky Survey. The decreasing part of the flare light curve roughly follows a power law t^−5/3. The quasar spectrum, the total energy of the flare, and the decline of the light curve are consistent with the tidal disruption of a ∼10 M_ʘ giant star by a supermassive black hole of a few 10⁸ M_ʘ. We argue that the alternative explanation by gravitational microlensing is less likely, though it cannot be definitely excluded.