Exploring plasma evolution during Sagittarius A* flares

Abstract

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.

Toward the event horizon—the supermassive black hole in the Galactic Center

“…Figure 2 Broad-band spectrum of Sgr A* compiled by [35], showing both the quiescent and flaring states. The black data points represent an average spectrum, compiled from [36], [37], with NIR upper limits from [38] and [39].…”

ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow

“…The radio emission is thought to originate mostly from partially self-absorbed synchrotron radiation emitted farther out from the black hole, while emission at frequencies corresponding to the submm bump (Falcke et al, 1998) of the Sgr A* spectrum is commonly associated with the optically thin emission closest to the black hole (Falcke et al, 1998;Shen et al, 2005;Bower, 2006;Doeleman et al, 2008). In the mm regime and at longer wavelengths, the flux density variation is thought to arise from local bulk properties (magnetic field strength, gas density, temperature) of the plasma, while the variability seen in infrared and X-rays is mostly attributed to changes in the population of the high-energy tail of the local electron energy distribution ( Özel et al, 2000;Markoff et al, 2001;Yuan et al, 2003;Dodds-Eden et al, 2010;Dibi et al, 2013).…”