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Discovery of the double quasar SDSS J1617+3827AB

ATel #10160; V. N. Shalyapin (IRE/NASU and University of Cantabria), A. V. Sergeyev (IRA/NASU and IoA/Kharkiv National University), L. J. Goicoechea (University of Cantabria), A. P. Zheleznyak (IRA/NASU and IoA/Kharkiv National University)
on 10 Mar 2017; 11:59 UT
Credential Certification: Luis J. Goicoechea (goicol@unican.es)

Subjects: Optical, Quasar, Gravitational Lensing

The optical spectroscopic follow-up of SDSS-III selected targets (Sergeyev et al. 2016MNRAS.456.1948S) has led to the discovery of the double quasar SDSS J1617+3827AB at redshift z = 2.079. The brighter image A (r ~ 19 mag) is located at (RA, Dec) = (16:17:52.92, +38:27:37.09), while the fainter image B (r ~ 21 mag) is only 2.1 arcsec apart from A at position angle PA = -20 deg (see SDSS database).

On the night of March 1, 2017, we obtained spectra of A and B with the instrument OSIRIS (R500B grism) on the 10.4-m Gran Telescopio CANARIAS. These identification observations consisted of 3x900s long-slit exposures in dark time and good seeing conditions (FWHM ~ 1 arcsec). The slit was oriented along the line joining A and B. As expected for a gravitationally lensed quasar, the two spectral energy distributions show identical emission-line redshifts, and the continuum flux ratio B/A is (nearly) independent of wavelength (Shalyapin et al. 2017, in preparation).

Archival spectra of A in the SDSS database suggest that the brightness of this image decreased in ~0.2 mag between April 2003 and May 2012, i.e., over a 9-year period. In addition, using SDSS (March 2003) and Maidanak Observatory (June 2015) frames in the r band, we report parallel changes in the r-band magnitude of both quasar images: dA ~ 0.3 mag and dB ~ 0.2 mag (brightness decrements). These results on the 10-year timescale variability of SDSS J1617+3827AB strongly support the feasibility of determining the time delay between A and B (detection of microlensing variations is also possible). A monitoring campaign of the new lensed quasar is out of the scope of our current observing programmes with 1-2m class telescopes, so we encourage monitoring efforts to address relevant astrophysical issues.

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