Fast giant flares in discs around supermassive black holes

Abstract

We studied the thermal stability of non-self-gravitating turbulent $\alpha$-discs around supermassive black holes (SMBHs) to test a new type of high-amplitude galactic nucleus flares. By calculating the disc structures, we computed the critical points of equilibrium curves for discs around SMBHs, which cover a wide range of accretion rates and resemble the shape $\xi$. We find that a transition of a disc ring from a recombined cold state to a hot, fully ionised, advection dominated, geometrically thick state is possible. Such a transition can trigger a giant flare for SMBHs with masses $\sim 10^6-10^8{M}_{\odot }$ if the prior geometrically thin and optically thick disc surrounded a central radiatively inefficient accretion flow. An increase in the viscosity parameter $\alpha$ is a necessary condition for this scenario. This increase may be related to the fact that the magnetic Prandtl number increases and exceeds 1 during ionisation. When self-gravity effects in the disc are negligible, the duration and power of the flare exhibit a positive correlation with the prior truncation radius of the geometrically thin disc. According to our estimates, the mass of about $\sim 4-3000M_{\odot }$ can be involved in the giant flare lasting 1 to 400 years if the flare is triggered somewhere between $60$ and $600$ gravitational radii from the SMBH of $10^7{M}_{\odot }$. The accretion rate on the SMBH peaks about 10 times faster at the potentially super-Eddington level. An optically thick outflow leads to anisotropy of the emission. At the beginning of the giant flare, the region near the truncation radius is heated to $\sim 10^5$K, and its UV/optical luminosity is at least $\sim 0.3-4L_{\mathrm{Edd}}$ depending on the SMBH mass. The sudden heating of a cold disc around a SMBH can trigger a massive outburst, similar in appearance to what is proposed to occur after a tidal disruption event.

main: 12 pages with 11 figures; appendix: 5 pages with 3 figures; figures have grids

References in corpus (32)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• Advection-Dominated Accretion and the Black Hole Event Horizon
• Simulations of star formation in a gaseous disc around sgr A* - a failed AGN
• Giant AGN Flares and Cosmic Ray Bursts
• A characteristic optical variability timescale in astrophysical accretion disks
• Slim disks around Kerr black holes revisited
• On the Magnetic Prandtl Number Behavior of Accretion Disks
• A likely decade-long sustained tidal disruption event
• Ultrafast Outflow in Tidal Disruption Event ASASSN-14li
• The spectral evolution of disc dominated tidal disruption events
• Fundamental scaling relationships revealed in the optical light curves of tidal disruption events
• A population of highly energetic transient events in the centres of active galaxies
• Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event
• Super-Eddington accretion discs with advection and outflows around magnetized neutron stars
• Modified models of radiation pressure instability in application to 10, 10${}^5$, and 10${}^7$ $M_{\odot }$ accreting black holes
• X-ray properties of TDEs
• An elliptical accretion disk following the tidal disruption event AT 2020zso
• The thermal-viscous disk instability model in the AGN context
• Saturation of the MRI in Strongly Radiation Dominated Accretion Disks
• SU Uma stars: Rebrightenings after superoutburst
• MRI-driven dynamo at very high magnetic Prandtl numbers
• Evolution of finite viscous disks with time-independent viscosity
• Optical polarization from colliding stellar stream shocks in a tidal disruption event
• Viscosity effects on waves in partially and fully ionized plasma in magnetic field
• A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213
• A Cigale module tailored (not only) for Low-Luminosity AGN
• The fast transient AT 2023clx in the nearby LINER galaxy NGC 3799 as a tidal disruption of a very low-mass star
• Scary Barbie: An Extremely Energetic, Long-Duration Tidal Disruption Event Candidate Without a Detected Host Galaxy at z = 0.995
• Long-term X-ray evolution of SDSS J134244.4+053056.1: A more than 18 year-old, long-lived IMBH-TDE candidate
• MRI turbulence in vertically stratified accretion discs at large magnetic Prandtl numbers
• Analysis of accretion disc structure and stability using open code for vertical structure