* Astronomy

Blobrana · L

SDSS J153636.22+044127.0

Blobrana · L

Title: J1536+0441 and the lack of evidence for close supermassive binary black holes
Authors: C. Martin Gaskell

It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this is a consequence of orbital motion of a supermassive blackhole binary (SMB). The AGN J1536+0441 (=SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon. It is proposed here instead that 1536+044 is an example of normal line emission from a disc in an AGN. Since SMB formation is expected to be common, and since J1536+0441 is the only sub-parsec SMB candidate suggested to date among ~ 17,500 SDSS AGNs with redshift, z < 0.70, a lack of clear optical spectral evidence for close SMBs is significant. If the line profiles in J1536+0441 are due to disc emission, rather than to two separate emission regions around the members of a SMB, this argues either that the merging of close SMBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted.

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Blobrana · L

Title: Discovery of Radio Emission from the Quasar SDSS J1536+0441, a Candidate Binary Black-Hole System
Authors: J.M. Wrobel, A. Laor

The radio-quiet quasar SDSS J1536+0441 shows two broad-line emission systems that Boroson & Lauer interpret as a candidate binary black-hole system with a separation of 0.1 pc (0.02 mas). From new VLA imaging at 8.5 GHz, two faint sources, separated by 0.97 arcsec (5.1 kpc), have been discovered within the quasar's optical localization region. Each radio source is unresolved, with a diameter of less than 0.37 arcsec (1.9 kpc). A double radio structure is seen in some other radio-quiet quasars, and the double may be energized here by the candidate 0.1-pc binary black-hole system. Alternatively, the radio emission may arise from a binary system of quasars with a projected separation of 5.1 kpc, and the two quasars may produce the two observed broad-line emission systems. Binary active galactic nuclei with a kpc scale separation are known from radio and X-ray observations, and a few such system are expected in the Boroson & Lauer sample based on the observed clustering of quasars down to the 10 kpc scale. Future observations designed to distinguish between the 0.1 pc and 5 kpc scales for the binary system are suggested.

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