Exploring plasma evolution during Sagittarius A* flares

Abstract

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*.

Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*

“…In the above description, σT is the Thomson cross section, kB is the Boltzmann constant, me is the electron mass, and c is the speed of light. There are only 4 free parameters to the model: l b , l nth , s, and linj, while the other parameters are set to standard values based on decades of multiwavelength fits from the quiescent spectrum (see Dibi et al 2014 and references therein). The prescribed acceleration process competes with injection, escape, and cooling losses to give the resulting particle distribution from which the emission is calculated.…”

“…The belm code was recently used to model the emission of two bright X-ray flares (2012 July 21th, and 2012 October 17th, Dibi et al 2014) with additional constraints from (non-simultaneous) IR flares. Two classes of models were studied: SD and SSC models.…”

“…This assumption is supported by the fact that the cooling time scales are typically very short (see Dibi et al 2014). In this paper we investigate several probabilistic models for the distributions of these parameters.…”

“…Dibi et al 2014). Compared to the synchrotron-dominated scenario however, the flaring activity implies variations of many physical properties of the accretion flow.…”

“…Observations and models agree on the fact that synchrotron emission by non-thermal relativistic electrons can account for the IR flares, but what exactly triggers electron acceleration is not modelled in detail and is therefore subject to interpretation (see e.g. Markoff et al 2001;Yuan et al 2003;Tagger & Melia 2006;Yuan et al 2009;Dodds-Eden et al 2010;Zubovas & Nayakshin 2012;Dibi et al 2014). …”