A light in the dark: searching for electromagnetic counterparts to black hole-black hole mergers in LIGO/Virgo O3 with the Zwicky Transient Facility

Matthew J. Graham, Barry McKernan, K. E. Saavik Ford, Daniel Stern, S. G. Djorgovski, Michael Coughlin, Kevin B. Burdge, Eric C. Bellm, George Helou, Ashish A. Mahabal, Frank J. Masci, Josiah Purdum, Philippe Rosnet, Ben Rusholme

September 2022

Abstract

The accretion disks of active galactic nuclei (AGN) are promising locations for the merger of compact objects detected by gravitational wave (GW) observatories. Embedded within a baryon-rich, high density environment, mergers within AGN are the only GW channel where an electromagnetic (EM) counterpart must occur (whether detectable or not). Considering AGN with unusual flaring activity observed by the Zwicky Transient Facility (ZTF), we describe a search for candidate EM counterparts to binary black hole (BBH) mergers detected by LIGO/Virgo in O3. After removing probable false positives, we find nine candidate counterparts to BBH mergers mergers during O3 (seven in O3a, two in O3b) with a $p$ -value of 0.019. Based on ZTF sky coverage, AGN geometry, and merger geometry, we expect $approx 3(N{rm BBH}/83)(f{rm AGN}/0.5) $p o t e n t i a l l y d e t e c t a b l e E M c o u n t e r p a r t s f r o m O 3, w h e r e$ N{rm BBH} $i s t h e t o t a l n u m b e r o f o b s e r v e d B B H m e r g e r s a n d$ f{rm AGN} $i s t h e f r a c t i o n o r i g i n a t i n g i n A G N . F u r t h e r m o d e l i n g o f b r e a k o u t a n d f l a r i n g p h e n o m e n a i n A G N d i s k s i s r e q u i r e d t o r e d u c e o u r f a l s e p o s i t i v e r a t e . T w o o f t h e e v e n t s a r e a l s o a s s o c i a t e d w i t h m e r g e r s w i t h t o t a l m a s s e s$ > 100M_odot $, w h i c h i s t h e e x p e c t e d r a t e f o r O 3 i f h i e r a r c h i c a l (l a r g e m a s s) m e r g e r s o c c u r i n t h e A G N c h a n n e l . C a n d i d a t e E M c o u n t e r p a r t s i n f u t u r e G W o b s e r v i n g r u n s c a n b e b e t t e r c o n s t r a i n e d b y c o v e r a g e o f t h e S o u t h e r n s k y a s w e l l a s s p e c t r a l m o n i t o r i n g o f u n u s u a l A G N f l a r i n g e v e n t s i n L I G O / V i r g o a l e r t v o l u m e s . A f u t u r e s e t o f r e l i a b l e A G N E M c o u n t e r p a r t s t o B B H m e r g e r s w i l l y i e l d a n i n d e p e n d e n t m e a n s o f m e a s u r i n g c o s m i c e x p a n s i o n ($ H_0$) as a function of redshift.

Type

Journal article

http://arxiv.org/abs/2209.13004v1