A Second Decoupling Between Merging Binary Black Holes and the Inner Disc--Impact on the Electromagnetic Counterpart

Abstract

The coalescence of two supermassive black holes (SMBHs) produces powerful gravitational-wave (GW) radiation and, if gas is present in the vicinity, also an electromagnetic (EM) counterpart. In the standard picture, an EM outburst will be produced when the binary "decouples" from the circum-binary disc and starts "squeezing" the disc inside the secondary orbit, resulting in its quick accretion on to the primary black hole. Here we use analytical arguments and numerical simulations to show that the disc within about $20R_S$ of a SMBH survives the merger without being depleted. The reason is a "second decoupling": the inner disc thickens due to tidal heating and inefficient cooling, effectively decoupling from the interaction of the binary. We show that this second decoupling quenches the heating sources in the disc $\mathcal{O}(10^2)$ days before coalescence. This will render the peak UV/X-ray luminosity significantly weaker than previously thought. After the merger, the residual disc cools down and expands, merging with the outer disc rather than being completely accreted. This results in continuous EM emission, hindering the detection of the cut-off and re-brightening proposed in earlier studies.

Submitted. Comments welcome!

References in corpus (7)

• Prompt Shocks in the Gas Disk Around a Recoiling Supermassive Black Hole Binary
• EM counterparts of recoiling black holes: general relativistic simulations of non-Keplerian discs
• Reaction of Accretion Disks to Abrupt Mass Loss During Binary Black Hole Merger
• Perturbed disks get shocked. Binary black hole merger effects on accretion disks
• On the search of electromagnetic cosmological counterparts to coalescences of massive black hole binaries
• Gas squeezing during the merger of a supermassive black hole binary
• Estimating the fossil disc mass during supermassive black hole mergers: the importance of torque implementation

Cited by in corpus (10)

• Black holes, gravitational waves and fundamental physics: a roadmap
• The late inspiral of supermassive black hole binaries with circumbinary gas discs in the LISA band
• Electromagnetic Counterparts to Massive Black Hole Mergers
• Probing gas disc physics with LISA: simulations of an intermediate mass ratio inspiral in an accretion disc
• A Single Progenitor Model for GW150914 and GW170104
• Non-steady-state long-term evolution of supermassive black hole binaries surrounded by accretion discs
• Astrophysics with the Laser Interferometer Space Antenna
• Identifying massive black hole binaries via light curve variability in optical time-domain surveys
• The effect of cooling on the accretion of circumprimary discs inmerging supermassive black hole binaries
• Massive black hole binaries in LISA: constraining cosmological parameters at high redshifts