GRMHD simulations of accretion onto Sgr A*: How important are radiative losses?

We present general relativistic magnetohydrodynamic (GRMHD) 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 modeling 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} Msun/yr i.e. Mdot < 10^{-7} Mdot_Edd. But 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.Comment: Resubmitted to MNRAS, including modifications in response to referee report. 13 pages, 15 figure

Current Status of Simulations

As the title suggests, the purpose of this chapter is to review the current status of numerical simulations of black hole accretion disks. This chapter focuses exclusively on global simulations of the accretion process within a few tens of gravitational radii of the black hole. Most of the simulations discussed are performed using general relativistic magnetohydrodynamic (MHD) schemes, although some mention is made of Newtonian radiation MHD simulations and smoothed particle hydrodynamics. The goal is to convey some of the exciting work that has been going on in the past few years and provide some speculation on future directions.Comment: 15 pages, 14 figures, to appear in the proceedings of the ISSI-Bern workshop on "The Physics of Accretion onto Black Holes" (8-12 October 2012

Fat Content and Fatty Acids Profile in Follow-on Formulas Commercialized in Côte d'Ivoire

This study evaluates the follow-on formula for infants. These products are available under several brands in the Ivorian market. In order to verify their conformity to the WHO standards a post-market control by gravimetric method and gas chromatography with mass spectrometry is executed to evaluate the quantity and quality of fat products contained in the milks of brands available in Côte d’Ivoire. Out of the nine brands of milks analyzed, only four of them were close to the values revealed by their manufacturers, whereas the other products had their values below their respective indications

THROMBASTHENIE DE GLANZMANN ET GROSSESSE : A PROPOS D’UN CAS COMPLIQUE D’HEMORRAGIE DE LA DELIVRANCE

Glanzmann's thrombasthenia is a rare hereditary, having autosomal recessive transmission, due to a deficiency of platelet membrane glycoprotein GPIIbIIIa, which is responsible for a decrease in platelet aggregation. It is the source of bleeding more or less important, appearing in childhood. Its association with pregnancy is rare, and may be complicated by bleeding. Mrs F.Z, a 23 years old primigravida, reaching Glanzmann’s thrombastenia since its infancy and has a postpartum hemorrhage that could be treated medically. We tried, through this case and a review of the literature, to review the management of this rare association, which may involve the prognosis of the mother.La thrombasthénie de Glanzmann est une maladie héréditaire rare, à transmission autosomale récessive, due à un déficit de la glycoprotéine membranaire plaquettaire GPIIbIIIa responsable d’une diminution de l’agrégation plaquettaire. Elle est à l'origine d'hémorragies plus ou moins importantes, apparaissant dès l'enfance. Son association avec la grossesse est rare, et peut se compliquer de plusieurs accidents hémorragiques. Nous rapportant le cas d’une primigeste de 23ans, connue porteuse d’une thrombasthénie de Glanzmann depuis son bas âge et qui présente une hémorragie de la délivrance qui a pu être jugulée médicalement. Nous avons essayé, à travers ce cas et une revue de la littérature, de mettre le point sur la prise en charge de cette association rare, qui peut mettre en jeu le pronostic vital maternel

L’INCONTINENCE URINAIRE DU POST PARTUM : INTERET DE LA REEDUCATION PERINEALE

The urinary incontinence is defined as the occurrence of involuntary urine leakage responsible for social or hygienic problem. The prevalence of symptoms of urinary incontinence increases during pregnancy and decreases spontaneously in the first three months in the postpartum. Several risk factors can be incriminated, some related to pregnancy and childbirth and others are constitutional. Prevention plays an important role and perineal rehabilitation gives good results.L’incontinence urinaire d’effort se définit comme la survenuede fuites involontaires d'urineresponsables d'un problème hygiénique ou social.La prévalence des symptômes d’incontinence urinaire augmente au cours de la grossesse puis diminue spontanément dans les trois premiers mois du post-partum. Plusieurs facteurs de risque peuvent être incriminés, certains sont liés à la grossesse et l’accouchement et d’autres sont constitutionnels. La prévention joue un rôle important et la rééducation périnéale donne de bons résultats

General Overview of Black Hole Accretion Theory

I provide a broad overview of the basic theoretical paradigms of black hole accretion flows. Models that make contact with observations continue to be mostly based on the four decade old alpha stress prescription of Shakura & Sunyaev (1973), and I discuss the properties of both radiatively efficient and inefficient models, including their local properties, their expected stability to secular perturbations, and how they might be tied together in global flow geometries. The alpha stress is a prescription for turbulence, for which the only existing plausible candidate is that which develops from the magnetorotational instability (MRI). I therefore also review what is currently known about the local properties of such turbulence, and the physical issues that have been elucidated and that remain uncertain that are relevant for the various alpha-based black hole accretion flow models.Comment: To be published in Space Science Reviews and as hard cover in the Space Sciences Series of ISSI: The Physics of Accretion on to Black Holes (Springer Publisher

Black hole spin: theory and observation

In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass has a standard Newtonian interpretation, the spin does not, with the effect of non-zero spin leaving an indelible imprint on the space-time closest to the black hole. As a consequence of relativistic frame-dragging, particle orbits are affected both in terms of stability and precession, which impacts on the emission characteristics of accreting black holes both stellar mass in black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN). Over the last 30 years, techniques have been developed that take into account these changes to estimate the spin which can then be used to understand the birth and growth of black holes and potentially the powering of powerful jets. In this chapter we provide a broad overview of both the theoretical effects of spin, the means by which it can be estimated and the results of ongoing campaigns.Comment: 55 pages, 5 figures. Published in: "Astrophysics of Black Holes - From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer: Astrophysics and Space Science Library. Additional corrections mad

Exploring plasma evolution during Sagittarius A* flares

Contains fulltext : 135204.pdf (preprint version ) (Open Access

Studying MHD and radiative processes in Sgr A*

This thesis details four different studies of accretion and emission processes around the Galactic Center Sgr A*. We are studying Sgr A* in particular because it is the closest supermassive black hole and therefore we have incomparable observational data to test our theories and predictions. However, as explained in the introduction, the physics is certainly similar to that around other supermassive black holes at the center of many other galaxies, and comparable as well to the accretion and emission processes around hundreds of millions of smaller mass black holes that are present in our Milky Way. It is interesting to understand what is happening around compact objects like black holes, because they are at the origin of the most energetic phenomena in the universe (such as jet launching) and therefore have an important role in its evolution. Moreover physical conditions around a black hole are extremely different to anything we can see and reproduce on Earth; Sgr A* is thus an excellent laboratory to test the limits of our understanding of compact objects and phenomena surrounding them