Fast giant flares in discs around supermassive black holes
G. V. Lipunova, A. S. Tavleev, K. L. Malanchev
arXiv:2404.08441v1 Announce Type: new
Abstract: We study the thermal stability of non-self-gravitating turbulent $alpha$ discs around supermassive black holes (SMBHs) to test a new type of high-amplitude active galactic nuclei (AGN) flares. On calculating discs structures, we compute the critical points of stability curves for discs around SMBH, which cover a wide range of accretion rates and resemble the shape of a $xi$ curve. We find that there are values of the disc parameters that favour the transition of a disc ring from a recombined cool state to a hot, fully ionised, advection dominated, geometrically thick state with higher viscosity parameter $alpha$. For SMBH with masses $sim 10^6-10^8 M_odot$, such a flare can occur in the geometrically thin and optically thick neutral disc with convective energy transfer through the disc thickness surrounding a radiatively inefficient accretion flow. When self-gravity effects are negligible, the duration of a flare and the associated mass exhibit a positive correlation with the truncation radius of the geometrically thin disc prior to the flare. According to our rough estimates, $sim 4-3000 M_odot$ can be involved in a giant flare, i.e. can be accreted or entrained with an outflow lasting 1 to 400 years, if the flare is triggered somewhere between $60$ and $600$ gravitational radii in a disc around SMBH with $10^7 M_odot$. The accretion rate on SMBH peaks at a super-Eddington value about ten times faster. The peak effective disc temperature at the trigger radius is $sim 10^5,$K, but it can be obscured by an optically thick outflow that reprocesses the emission to longer wavelengths. Such a transfer of disc state could trigger a massive outburst, similar to that following a tidal disruption event.arXiv:2404.08441v1 Announce Type: new
Abstract: We study the thermal stability of non-self-gravitating turbulent $alpha$ discs around supermassive black holes (SMBHs) to test a new type of high-amplitude active galactic nuclei (AGN) flares. On calculating discs structures, we compute the critical points of stability curves for discs around SMBH, which cover a wide range of accretion rates and resemble the shape of a $xi$ curve. We find that there are values of the disc parameters that favour the transition of a disc ring from a recombined cool state to a hot, fully ionised, advection dominated, geometrically thick state with higher viscosity parameter $alpha$. For SMBH with masses $sim 10^6-10^8 M_odot$, such a flare can occur in the geometrically thin and optically thick neutral disc with convective energy transfer through the disc thickness surrounding a radiatively inefficient accretion flow. When self-gravity effects are negligible, the duration of a flare and the associated mass exhibit a positive correlation with the truncation radius of the geometrically thin disc prior to the flare. According to our rough estimates, $sim 4-3000 M_odot$ can be involved in a giant flare, i.e. can be accreted or entrained with an outflow lasting 1 to 400 years, if the flare is triggered somewhere between $60$ and $600$ gravitational radii in a disc around SMBH with $10^7 M_odot$. The accretion rate on SMBH peaks at a super-Eddington value about ten times faster. The peak effective disc temperature at the trigger radius is $sim 10^5,$K, but it can be obscured by an optically thick outflow that reprocesses the emission to longer wavelengths. Such a transfer of disc state could trigger a massive outburst, similar to that following a tidal disruption event.