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A prominent fluctuation in the optical brightness of Q0957+561A and prediction of the Q0957+561B optical variability in the first semester of 2010

ATEL # 2228; Luis J. Goicoechea (Universidad de Cantabria, Spain) and Vyacheslav N. Shalyapin (Institute for Radiophysics and Electronics, Ukraine)
on 5 Oct 2009; 19:31 UT
Password Certification: Luis J. Goicoechea (goicol@unican.es)

Subjects: Optical, Request for Observations, AGN, Quasars, Transients

We are conducting a long-term monitoring of the optical magnitudes of gravitationally lensed quasars using the 2.0 m Liverpool Robotic Telescope at the Roque de los Muchachos Observatory (Canary Islands, Spain). This Liverpool Quasar Lens Monitoring (LQLM) programme includes several lensed quasars whose images are as bright as or brighter than 19 mag in the r-band (SDSS photometric system). One of our targets is Q0957+561 (RA=10:01:20.78, Dec=+55:53:49.4), which consists of two images of the same distant quasar at z=1.41. These images Q0957+561A and Q0957+561B are separated by about 6 arcsec. From the LQLM photometric pipelines (Shalyapin et al. 2008, A&A, 492, 401), we detected a strong quasar activity over the last three years. In particular, the g-band flux of the leading image Q0957+561A increases 30% just after a deep minimum, i.e., it changes from g~17.45 to g~17.15 over about 130 days. We also observe a significant increase (~20%) in the r-band flux of Q0957+561A, which confirms the existence of an optical event. The most recent LQLM observations of Q0957+561A (first semester of 2009) show this event has peaked and later decreased in brightness.

As the the prominent fluctuation in the optical brightness of Q0957+561A occured berween late 2008 and the middle of 2009, it is expected a similar fluctuation in the light curve of the trailing image Q0957+561B in the first semester of 2010, starting in early February and reaching its maximum in June (taking a time delay of about 14 months into account; the g-band brightening of Q0957+561B will probably behave like the red circles between the two vertical blue arrows in the figure http://grupos.unican.es/glendama/ATel.png). Consequently, we strongly encourage multiwavelength observations of Q0957+561B. Although we will try to monitor this target in 2010 in the g and r bands (and perhaps using other optical/NIR filters), additional spectrophotometry at X-ray, UV, optical, IR and radio wavelengths should play a crucial role in the understanding of the variability mechanism and other aspects of the distant source. For example, it could be possible to accurately check if the observed optical event (which corresponds to middle UV emission at the redshift of the quasar) is triggered (and thus preceded) by a higher energy flare.

GLENDAMA project


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