We present general relativistic magnetohydrodynamic numerical simulations of the accretion flow around the supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*). The simulations include for the first time radiative cooling processes (synchrotron, bremsstrahlung and inverse Compton) self‐consistently in the dynamics, allowing us to test the common simplification of ignoring all cooling losses in the modelling of Sgr A*. We confirm that for Sgr A*, neglecting the cooling losses is a reasonable approximation if the Galactic Centre is accreting below ∼10−8 M⊙ yr−1, i.e. Ṁ<10−7trueṀ Edd . However, above this limit, we show that radiative losses should be taken into account as significant differences appear in the dynamics and the resulting spectra when comparing simulations with and without cooling. This limit implies that most nearby low‐luminosity active galactic nuclei are in the regime where cooling should be taken into account. We further make a parameter study of axisymmetric gas accretion around the supermassive black hole at the Galactic Centre. This approach allows us to investigate the physics of gas accretion in general, while confronting our results with the well‐studied and observed source, Sgr A*, as a test case. We confirm that the nature of the accretion flow and outflow is strongly dependent on the initial geometry of the magnetic field. For example, we find it difficult, even with very high spins, to generate powerful outflows from discs threaded with multiple, separate poloidal field loops.

We present a new way of describing the flares from Sgr A* with a self-consistent calculation of the particle distribution. All relevant radiative processes are taken into account in the evolution of the electron distribution and resulting spectrum. We present spectral modelling for new X-ray flares observed by NuSTAR, together with older observations in different wavelengths, and discuss the changes in plasma parameters to produce a flare.We show that under certain conditions, the real particle distribution can differ significantly from standard distributions assumed in most studies.We conclude that the flares are likely generated by magnetized plasma consistent with our understanding of the accretion flow. Including non-thermal acceleration, injection, escape, and cooling losses produces a spectrum with a break between the infrared and the X-ray, allowing a better simultaneous description of the different wavelengths. We favour the non-thermal synchrotron interpretation, assuming the infrared flare spectrum used is representative.We also consider the effects on Sgr A*s quiescent spectrum in the case of a density increase due to the G2 encounter with Sgr A*.

We present the first spectral energy distributions produced self-consistently by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical simulations, where radiative cooling is included in the dynamical calculation. As a case study, we focus on the accretion flow around the supermassive black hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best constrained physical parameters. We compare the simulated spectra to the observational data of Sgr A* and explore the parameter space of our model to determine the effect of changing the initial magnetic field configuration, ion to electron temperature ratio T i /T e and the target accretion rate. We find the best description of the data for a mass accretion rate of ∼ 10 −9 M ⊙ /yr, and rapid spin (0.7 < a * < 0.9). The submillimeter peak flux seems largely independent of initial conditions, while the higher energies can be very sensitive to the initial magnetic field configuration. Finally, we also discuss flaring features observed in some simulations, that may be due to artifacts of the 2D configuration.

The supermassive black hole at the centre of the Galaxy flares at least daily in the infrared (IR) and X-ray bands, yet the process driving these flares is still unknown. So far detailed analysis has only been performed on a few bright flares. In particular, the broadband spectral modelling suffers from a strong lack of simultaneous data. However, new monitoring campaigns now provide data on thousands of flaring events, allowing a statistical analysis of the flare properties. In this paper, we investigate the X-ray and IR flux distributions of the flare events.Using a self-consistent calculation of the particle distribution, we model the statistical properties of the flares. Based on a previous work on single flares, we consider two families of models: pure synchrotron models and synchrotron self-Compton (SSC) models. We investigate the effect of fluctuations in some relevant parameters (e.g. acceleration properties, density, magnetic field) on the flux distributions. The distribution of these parameters is readily derived from the flux distributions observed at different wavelengths.In both scenarios, we find that fluctuations of the power injected in accelerated particles plays a major role. This must be distributed as a power-law (with different indices in each model). In the synchrotron dominated scenario, we derive the most extreme values of the acceleration power required to reproduce the brightest flares. In that model, the distribution of the acceleration slope fluctuations is constrained and in the SSC scenario we constrain the distributions of the correlated magnetic field and flow density variations.

The fundamental plane of black hole activity is an empirical relationship between the OIII/X-ray luminosity depicting the accretion power, the radio luminosity as a probe of the instantaneous jet power and the mass of the black hole. For the first time, we use the 1.4 GHz FIRST radio luminosities on the optical fundamental plane, to investigate whether or not FIRST fluxes can trace nuclear activity. We use a SDSS-FIRST cross-correlated sample of 10149 active galaxies and analyse their positioning on the optical fundamental plane. We focus on various reasons that can cause the discrepancy between the observed FIRST radio fluxes and the theoretically expected core radio fluxes, and show that that FIRST fluxes are heavily contaminated by non-nuclear, extended components and other environmental factors. We show that the subsample of 'compact sources', which should have negligible lobe contribution, statistically follow the fundamental plane when corrected for relativistic beaming, while all the other sources lie above the plane. The sample of LINERs, which should have negligible lobe and beaming contribution, also follow the fundamental plane. A combined fit of the low-luminosity AGN and the X-ray binaries, with the LINERs, results in the relation log L R = 0.77 log L OIII + 0.69 log M. Assuming that the original fundamental plane relation is correct, we conclude that 1.4 GHz FIRST fluxes do not trace the pure 'core' jet and instantaneous nuclear activity in the AGN, and one needs to be careful while using it on the fundamental plane of black hole activity.

We present a new way of describing the flares occurring from Sgr A* within a single zone with a self-consistent calculation of the particle distribution. The results allow us to give an interpretation to the flaring events generated very close to the supermassive black hole (SMBH) without assuming a specific particle distribution. We conclude that the flare data are more likely generated by a weakly magnetized plasma in which the particles flow in and out as expected from an accretion flow. Such a plasma, with prescription for non-thermal acceleration, injection, escape, and cooling losses, gives a spectrum with a break between the infra-red and the X-ray, allowing a better simultaneous match in the different wavelengths. The parameters favor the non-thermal synchrotron spectrum, and a decrease/increase of the magnetic field and plasma density are not favored for producing the flare event, but particle acceleration must be happening by other means. We show that under certain conditions, the real particle distribution can differ significantly from the standard distributions used in such studies.

Abstract. Cosmos++ (Anninos et al 2005) is one of the first fully relativistic magneto-hydrodynamical (MHD) codes that can self-consistently account for radiative cooling, in the optically thin regime. As the code combines a total energy conservation formulation with a radiative cooling function, we have now the possibility to produce spectra energy density from these simulations and compare them to data. In this paper, we present preliminary results of spectra calculated using the same cooling functions from 2D Cosmos++ simulations of the accretion flow around Sgr A*. The simulation parameters were designed to roughly reproduce Sgr A*'s behavior at very low ( 10 −8 -10 −7 M /yr) accretion rate, but only via spectra can we test that this has been achieved.

Abstract. We obtained the first spectral predictions from a simulation of the Galactic Center to include radiative processes internally. We performed simulations with and without cooling, with and without spin, and for different initial configurations of the magnetic field, in order to test the effect on jet launching and inner accretion disk characteristics. By exploring parameter space, we will attempt to place new constraints on the controversial question about the presence or not of a jet from Sgr A*, as well as study jet launching in general. We have shown that, as expected, the spin of the BH affects the structure of the jet. The presence of cooling also strongly influences the inner structure of the accretion disk and therefore affects jet launching. These results show that radiative cooling is not negligible, as is usually assumed for the very underluminous supermassive BH, Sgr A*. On the contrary, the inclusion of cooling has a very visible influence on the accretion disk. Furthermore it creates an important difference in the resulting spectra.