Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g*
Abstract
We report the first plausible optical electromagnetic counterpart to a (candidate) binary black hole merger. Detected by the Zwicky Transient Facility, the electromagnetic flare is consistent with expectations for a kicked binary black hole merger in the accretion disk of an active galactic nucleus [B. McKernan, K. E. S. Ford, I. Bartos et al., Astrophys. J. Lett. 884, L50 (2019), 10.3847/2041-8213/ab4886] and is unlikely [<O (0.01 %) )] due to intrinsic variability of this source. The lack of color evolution implies that it is not a supernova and instead is strongly suggestive of a constant temperature shock. Other false-positive events, such as microlensing or a tidal disruption event, are ruled out or constrained to be <O (0.1 %) . If the flare is associated with S190521g, we find plausible values of total mass MBBH∼100 M⊙, kick velocity vk∼200 km s-1 at θ ∼6 0 ° in a disk with aspect ratio H /a ∼0.01 (i.e., disk height H at radius a ) and gas density ρ ∼10-10 g cm-3 . The merger could have occurred at a disk migration trap (a ∼700 rg; rg≡G MSMBH/c2, where MSMBH is the mass of the active galactic nucleus supermassive black hole). The combination of parameters implies a significant spin for at least one of the black holes in S190521g. The timing of our spectroscopy prevents useful constraints on broad-line asymmetry due to an off-center flare. We predict a repeat flare in this source due to a reencountering with the disk in ∼1.6 yr (MSMBH/108 M⊙)(a /103rg)3 /2 .
- Publication:
-
Physical Review Letters
- Pub Date:
- June 2020
- DOI:
- 10.1103/PhysRevLett.124.251102
- arXiv:
- arXiv:2006.14122
- Bibcode:
- 2020PhRvL.124y1102G
- Keywords:
-
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 9 pages, 4 figures, accepted for publication in Physical Review Letters (June 25, 2020)