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SDSS J1536+0441: A quasar pair, not a binary black hole

ATEL # 2061; R. Decarli, A. Treves (Universita` dell'Insubria - Como); R. Falomo (INAF-Osservatorio Astronomico di Padova); M. Dotti (University of Michigan); M. Colpi (Universita` di Milano-Bicocca); J.K. Kotilainen (Tuorla Observatory - University of Turku)
on 27 May 2009; 21:52 UT
Password Certification: Roberto Decarli (roberto.decarli@mib.infn.it)

Subjects: Infra-Red, Binaries, Quasars

We report on a deep K-band image of the quasar SDSS J1536+0441 (SDSS J153636.22+044127.0; RA: 15h36m36s.2, Dec: +04o41'28") by using HAWK-I at the ESO/VLT on 2009 April 30.29 (DDT 282.B-5059).

The spectrum of this radio quiet QSO (z=0.3893) exhibits two broad emission line systems at slightly different redshifts (DeltaV=3300 km/s) in the SDSS optical spectrum and was thus proposed as a candidate binary massive black hole system with sub-parsec separation (Boroson & Lauer 2009, Nature 458, 53) or a double-peaked broad emission line (Chornock et al. 2009, ATEL #1955; Gaskell 2009, arXiv:0903.4447).

Our new image shows that SDSS J1536+0441 is composed of two sources (with K=14.1 and 15.8) at the separation of 1'' (5.3 kpc). Both the sources consist of a nucleus plus an extended emission. The host galaxies have K=15.6 and 16.2.

These results strongly suggest that SDSS J1536+0441 is a kpc-scale pair of quasars. This interpretation is consistent with the recent finding of two compact radio sources by Wrobel & Laor, 2009, arXiv:0905.3566. In this picture, SDSS J1536+0441 represents one of the closest quasar pair ever discovered.


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