The flux distribution of Sgr A*

Abstract

The Galactic center black hole Sagittarius A* is a variable near-infrared (NIR) source that exhibits bright flux excursions called flares. When flux from Sgr A* is detected, the light curve has been shown to exhibit red noise characteristics and the distribution of flux densities is non-linear, non-Gaussian, and skewed to higher flux densities. However, the low-flux density turnover of the flux distribution is below the sensitivity of current single-aperture telescopes. For this reason, the median NIR flux has only been inferred indirectly from model fitting, but it has not been directly measured. In order to explore the lowest flux ranges, to measure the median flux density, and to test if the previously proposed flux distributions fit the data, we use the unprecedented resolution of the GRAVITY instrument at the VLTI. We obtain light curves using interferometric model fitting and coherent flux measurements. Our light curves are unconfused, overcoming the confusion limit of previous photometric studies. We analyze the light curves using standard statistical methods and obtain the flux distribution. We find that the flux distribution of Sgr A* turns over at a median flux density of (1.1 ± 0.3) mJy. We measure the percentiles of the flux distribution and use them to constrain the NIR K-band spectral energy distribution. Furthermore, we find that the flux distribution is intrinsically right-skewed to higher flux density in log space. Flux densities below 0.1 mJy are hardly ever observed. In consequence, a single powerlaw or lognormal distribution does not suffice to describe the observed flux distribution in its entirety. However, if one takes into account a power law component at high flux densities, a lognormal distribution can describe the lower end of the observed flux distribution. We confirm the rms–flux relation for Sgr A* and find it to be linear for all flux densities in our observation. We conclude that Sgr A* has two states: the bulk of the emission is generated in a lognormal process with a well-defined median flux density and this quiescent emission is supplemented by sporadic flares that create the observed power law extension of the flux distribution.

Can Black Holes or Other Relativistic Space Objects Be a Source of Dark Energy?

“…It is orbiting Sgr A* with a period of 16.0518 years, a semi-major axis of about 970 au, and a pericenter distance of 17 light hours (18 Tm or 120 au). Analysis of its motion confirmed the conclusions of general relativity [12]. The orbits of S2 and other stars in the vicinity of Sgr A* are close to ellipses.…”

“…The authors of [4] rightly point out that we do not know a solution that describes even a Schwarzschild BH, not to mention a Kerr one, against the background of a homogeneous isotropic FLRW space-time. Let us assume that in this incomprehensible situation we can accept Formula (10) with the value k ≃ 3 according to (11) or (12) as a hypothesis or an empirical relationship.…”

Modeling Wormholes Generated by Dark Matter Galactic Halos in f(R)$f(R)$ Modified Gravity

“…The field equations can be made simpler using the trace Equation (5), which can then be exploited as a restraint factor. Consequently, by inserting the trace equation in Equation ( 3) and rearranging the components, we arrive at the gravitational field equation shown below,…”

“…In recent times, the study of gravitational physics and space‐time geometry has been a spotlight research area because of several experimental tests like LIGO, [ 1 ] ATHENA, [ 2 ] Event horizon telescope, [ 3,4 ] Virgo, [ 5 ] Gamma‐Ray Astrophysics Laboratory, [ 6 ] and so on. Alongside already known to be existing objects like compact stars, and black holes, some interesting but yet hypothetical geometries like wormholes (WHs) are also very fascinating to study in the context of gravitational physics.…”

Appearance of an Infalling Star in Black Holes with Multiple Photon Spheres

“…Apart from stationary observational appearances of black holes, photon spheres also play an important role in dynamic observations of luminous objects around black holes. A particularly interesting scenario is luminous matter freely falling onto black holes, which occurs frequently and was reported near the Cyg X-1 black hole [89] and the Sgr A* source [90,91]. Recently, the authors of [92] numerically simulated the appearance of a point-like source, which emits photons or gravitons as it falls into a Schwarzschild black hole.…”