Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational Wave Event S190521g

M. J. Graham, K. E. S. Ford, B. McKernan, N. P. Ross, D. Stern, K. Burdge, M. Coughlin, S. G. Djorgovski, A. J. Drake, D. Duev, M. Kasliwal, A. A. Mahabal, S. van Velzen, J. Belicki, E. C. Bellm, R. Burruss, S. B. Cenko, V. Cunningham, G. Helou, S. R. Kulkarni, F. J. Masci, T. Prince, D. Reiley, H. Rodriguez, B. Rusholme, R. M. Smith, M. T. Soumagnac

June 2020

Abstract

We report the first plausible optical electromagnetic (EM) counterpart to a (candidate) binary black hole (BBH) merger. Detected by the Zwicky Transient Facility (ZTF), the EM flare is consistent with expectations for a kicked BBH merger in the accretion disk of an active galactic nucleus (AGN), and is unlikely ( $< O (0.01$ )) due to intrinsic variability of this source. The lack of color evolution implies that it is not a supernovae 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 $ M{rm BBH} sim 100 M{odot} $, k i c k v e l o c i t y$ vk sim 200, {rm km}, {rm s}^{-1} $a t$ theta sim 60^{circ} $i n a d i s k w i t h a s p e c t r a t i o$ H/a sim 0.01 $(i . e ., d i s k h e i g h t$ H $a t r a d i u s$ a $) a n d g a s d e n s i t y$ rho sim 10^{-10}, {rm g}, {rm cm}^{-3} $. T h e m e r g e r c o u l d h a v e o c c u r r e d a t a d i s k m i g r a t i o n t r a p ($ a sim 700, r{g} $;$ rg equiv G M{rm SMBH} / c^2 $, w h e r e$ M{rm SMBH} $i s t h e m a s s o f t h e A G N s u p e r m a s s i v e b l a c k h o l e) . T h e c o m b i n a t i o n o f p a r a m e t e r s i m p l i e s a s i g n i f i c a n t s p i n f o r a t l e a s t o n e o f t h e b l a c k h o l e s i n S 190521 g . T h e t i m i n g o f o u r s p e c t r o s c o p y p r e v e n t s u s e f u l c o n s t r a i n t s o n b r o a d - l i n e a s y m m e t r y d u e t o a n o f f - c e n t e r f l a r e . W e p r e d i c t a r e p e a t f l a r e i n t h i s s o u r c e d u e t o a r e - e n c o u n t e r i n g w i t h t h e d i s k i n$ sim 1.6, {rm yr}, (M{rm SMBH}/10^{8}M{odot}), (a/10^{3}r{g})^{³⁄₂}$.

Type

Journal article

http://arxiv.org/abs/2006.14122v1