X-ray echoes of infrared flaring in Sgr A*

TL;DR

This paper models the upscattering of infrared flare photons by thermal electrons in Sgr A*'s accretion flow, producing X-ray emissions that match observed flare luminosities and constraining accretion flow properties.

Contribution

It introduces a new model for X-ray flares in Sgr A* based on upscattering of infrared photons by thermal electrons, providing testable predictions for accretion flow characteristics.

Findings

Peak X-ray luminosities match observed flares.

Model constrains electron density and temperature profiles.

Future observations can test the model's predictions.

Abstract

Sgr A* exhibits flaring in the infrared several times each day, occasionally accompanied by flaring in X-rays. The infrared flares are believed to arise through synchrotron emission from a transient population of accelerated electrons. The X-ray flaring has been interpreted as self-synchrotron-compton, inverse compton, or synchrotron emission associated with the transient electrons. Here I consider the upscattering of infrared flare photons by relativistic thermal electrons in the accretion flow around Sgr A*. Typical profiles of electron density and temperature in the accretion flow are adopted and the X-ray light curves produced by upscattering of infrared flare photons by the accretion flow are computed. Peak X-ray luminosities between 1e33 and 1e34 erg/s are attained for a 10 mJy near-infrared flare, compatible with observed coincident infrared/X-ray flares from Sgr A*. Even if this process is not responsible for the observed flares it still presents a serious constraint on accretion flow models, which must avoid over-producing X-rays and also predicting observable time lags between flaring in infrared and in X-rays. Future high-resolution infrared instrumentation will be able to place the location of the infrared flare and in coordination with the X-ray would severely constrain the disc geometry and the radial profiles of electron density and temperature in the accretion flow.