Multiple accretion events as a trigger for Sgr A* activity

Abstract

Gas clouds are present in the Galactic centre, where they orbit around the supermassive black hole. Collisions between these clumps reduce their angular momentum, and as a result some of the clumps are set on a plunging trajectory. Constraints can be imposed on the nature of past accretion events based on the currently observed X-ray reflection from the molecular clouds. We discuss accretion of clouds in the context of enhanced activity of Sgr A* during the past few hundred years. We put forward a scenario according to which gas clouds bring material close to the horizon of the black hole on <~0.1 parsec scale. We have modelled the source intrinsic luminosity assuming that multiple events occur at various moments in time. These events are characterized by the amount of accreted material and the distribution of angular momentum. We parameterized the activity in the form of a sequence of discrete events, followed the viscous evolution, and calculated the luminosity of the system from the time-dependent accretion rate across the inner boundary. Accreting clumps settle near a circularization radius, spread there during the viscous time, and subsequently feed the black hole over a certain period. A significant enhancement (by factor of ten) of the luminosity is only expected if the viscous timescale of the inflow is very short. On the other hand, the increase in source activity is expected to be much less prominent if the latter timescale is longer and a considerable fraction of the material does not reach the centre. A solution is obtained under two additional assumptions: (i) the radiative efficiency is a decreasing function of the Eddington ratio; (ii) the viscous decay of the luminosity proceeds somewhat faster than the canonical L(t)~t^{-5/3} profile. We applied our scheme to the case of G2 cloud in the Galactic centre to obtain constraints on the core-less gaseous cloud model.

Astronomy and Astrophysics accepted

References in corpus (10)

• Advection-Dominated Accretion and the Black Hole Event Horizon
• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• Galactic Centre stellar winds and Sgr A* accretion
• Variable accretion and emission from the stellar winds in the Galactic centre
• A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole
• Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center
• Simultaneous NIR/sub-mm observation of flare emission from SgrA*
• Accretion of cool stellar winds on Sgr A*: another puzzle of the Galactic Centre?
• Numerical simulations of the possible origin of the two sub-parsec scale and counter-rotating stellar disks around SgrA*
• Coordinated NIR/mm observations of flare emission from Sagittarius A*

Cited by in corpus (14)

• Monitoring the Dusty S-Cluster Object (DSO/G2) on its Orbit towards the Galactic Center Black Hole
• Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei
• The Properties and Fate of the Galactic Center G2 Cloud
• Depletion of bright red giants in the Galactic center during its active phases
• Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate
• Constraining the accretion flow density profile near Sgr A* using the $L^{\prime }$-band emission of the S2 star
• Modeling Hot Gas Flow in the Low-Luminosity Active Galactic Nucleus of NGC3115
• Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed
• Multi-phase environment of compact galactic nuclei: the role of the Nuclear Star Cluster
• The multi-phase environment in the centre of Centaurus A
• X-ray observations of the hot phase in Sgr~A*
• The Galactic Center Black Hole Laboratory
• M31 nucleus: molecular and ionised gas content upper limits
• High Energy Emission from the Galactic Center