Electromagnetic counterparts of supermassive black hole binaries resolved by pulsar timing arrays

摘要: Pulsar timing arrays (PTAs) are expected to detect gravitational waves (GWs) from individual low-redshift (z≲ 1.5) compact supermassive (M≳ 109 M⊙) black hole (SMBH) binaries with orbital periods of ∼0.1–10 yr. Identifying the electromagnetic (EM) counterparts these sources would provide confirmation putative direct detections GWs, present a rare opportunity study environments SMBH and could enable use as standard sirens for cosmology. Here we consider feasibility such an EM identification. We show that because host galaxies resolved PTA be exceptionally massive rare, it should possible find unique hosts out z≈ 0.2. At higher redshifts, error boxes larger, may contain many ∼100 massive-galaxy interlopers. The number candidates, however, remains tractable follow-up searches in upcoming wide-field surveys. develop toy model characterize dynamics thermal emission geometrically thin gaseous disc accreting on PTA-source binary. Our predicts at optical infrared frequencies, source appear similar typical luminous active galactic nucleus (AGN). However, owing evacuation accretion flow by binary’s tidal torques, might have unusually low soft X-ray luminosity weak ultraviolet (UV) broad lines, compared AGN powered single same total mass. For z∼ 1, decrement rest-frame UV observable extremely red colour. These properties make stand among optically AGN, allow their results also suggest included observed population bright, X-ray-dim AGN.